cdma air interfaces

CL8300-SG.en.UL 1

Student GuideUnderstanding the CDMA Air-Interfaces of IS-95, IS-2000, and IS-856CL8300

CL8300-SG.en.ULIssue 1.0

June 2003

Lucent Technologies - ProprietaryUse pursuant to Company instructions

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This material is protected by the copyright and trade secret laws of the United States and other countries. It may not be reproduced, distributed, or altered in any fashion by any entity (either internal or external to Lucent Technologies), except in accordance with applicable agreements, contracts, or licensing, without the express written consent of Lucent Technologies and the business management owner of the material.

Copyright © 2003 Lucent Technologies. All Rights Reserved.

Notice

Every effort was made to ensure that this information product was complete and accurate at the time of printing. However, information is subject to change.

Mandatory customer information

This information product does not contain any mandatory customer information.

Trademarks

Flexent is a registered trademark of Lucent Technologies.

AUTOPLEX is a registered trademark of Lucent Technologies.

5ESS is a registered trademark of Lucent Technologies.

Adobe Acrobat is a trademark of Adobe Systems, Inc.

cdmaOne is a registered trademark of the CDMA Development Group

CDMA2000 is a registered trademark of the Telecommunications Industry Association (TIA-USA)

WatchMark is a registered trademark of WatchMark Corp.

Prospect is a trademark of WatchMark Corp.

Technical support

For technical support, see “To obtain documentation, training, and technical support or submit feedback” on the 401-010-001 Flexent®/AUTOPLEX® Wireless Networks System Documentation CD-ROM or the documentation web site at https://wireless.support.lucent.com/

Developed by Lucent Technologies

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Course plan prologue

Course overview

Course description

Provides an in-depth understanding of the CDMA air-interface technologies and concepts for IS-95, IS-2000, and IS-856.

Course objectives

This course is designed to enable you to:

•Demonstrate the process of spreading and despreading

•Explain how processing gain is achieved

•Analyze the coding steps performed on the digital signal

•Compare the CDMA codes used in signal processing

•Illustrate the fundamental call processing phases

•Differentiate between IS-95, IS-2000, and IS-856.

Course outline

This course covers:

•Understanding of wireless radio concepts

•In-depth discussion of CDMA concepts, characteristics, and signal processing

•Discussion of the IS-95, IS-2000, and IS-856 channels and their coding

•Core call processing as specified by IS-95, IS-2000, and IS-856

Mode of delivery

This course is offered as an instructor-led or self-paced course.

Media

Instructor-led course:

•Paper-based student guide

•Power Point presentation

Self-paced course:

•Web-browser

Duration

The class length for the instructor-led course is 4 days.

The class length for the self-paced course is 20 hours.

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Related courses

Other Lucent Technologies courses related to CL8300 include the following:

CL8301: CDMA IS-95 and 3G-1X Design and Growth Engineering for Cellular Systems

This course provides engineering training in RF design of coverage and capacity for Lucent Technologies cellular (850 MHz) CDMA systems. The course covers both cdmaOne (IS-95) and CDMA2000 (IS-2000).

CL8302: CDMA IS-95 and 3G-1X RF Design and Growth Engineering for PCS Systems

Similar to CL8301 but for a PCS (1900 MHz) system.

CL8303: CDMA IS-95 and 3G-1X Base Station Call Processing

This course provides engineering training in base station call processing for Lucent Technologies CDMA systems. The course covers both cdmaOne (IS-95) and CDMA2000 (IS-2000) as well as cellular (850MHz) and PCS (1900MHZ) systems.

CL8304: CDMA 3G-1X RF Design Engineering and Base Station Call Processing

This course provides training in RF design of coverage and capacity, and base station call processing for Lucent Technologies CDMA systems. The course covers IS-2000 (3G-1X). The course is used as a "delta" course to give students with the prerequisites the necessary knowledge to operate a 3G system.

CL8306: 1xEV-DO RF Design Engineering and Call Processing

This course provides experienced engineers the needed training to design a Lucent Technologies 1xEV-DO system for RF coverage and capacity. The course also provides thorough understanding of the call processing algorithms in the access terminals and base stations.

CL3723: Wireless AMPS/PCS CDMA RF Performance Engineering

This course provides a basic overview of the RF engineering optimization processes unique to CDMA. Lucent Technologies's suggested optimization techniques are discussed utilizing case study data gathered from in-service systems that have recently been optimized.

CL1522: WatchMark® Prospect™ - Lucent® Technologies AMPS/CDMA/TDMA Operations

This course is designed to instruct students in the use of the Prospect applications.

CL1523: WatchMark® Prospect™ - Lucent® Tech.-Special Engineering Studies Operations

This course is designed to instruct students in the use of the Prospect SES applications.

Course registration

Register for a course via the web or over the phone:

http://www.lucent.com/training

1-888-LUCENT8 (582-3688) (within the U.S.A.)

+1-407-767-2667 (outside the U.S.A.)

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Lucent Technologies - Proprietary5

Understanding the CDMAAir-InterfacesCL8300

CDMA RF Engineering Curriculum History

CDMAFundamentals

RF DesignEngineering

Base StationCall Processing

RF PerformanceEngineering

Topic R12 - R16 R17+

CL3721/CL3722/CL3725

2G

CL83043G-1XDelta

CL37232G

CL37232G/3G-1X

CL37152G

CL37152G

CL8301/CL83022G/3G-1X

CL83032G/3G-1X

System PerformanceMonitoring andAnalysis Tools

CL1517/CL1518/CL1522

CL1522/CL1523

CL83061xEV-DO

(R18+)

CL83002G/3G-1X/1xEV-DO

CL37163G-1X

Overview

References

The following publications are major references for this course:

•TIA/EIA/IS-95-A, “Mobile Station-Base Station Compatibility Standard for Wideband Spread Spectrum Cellular Systems”

•TIA/EIA-95-B, “Mobile Station-Base Station Compatibility Standard for Wideband Spread Spectrum Cellular Systems”

•TIA/EIA/IS-2000A - Family of standards for “CDMA2000 Standards for Spread SpectrumSystems”

•TIA/EIA/IS-856, “CDMA2000 High Rate Packet Data Air Interface Specification”

These publications can be ordered from TIA (http://www.tiaonline.com)

Note:CL3715, CL3721, CL3722, CL3725,CL1517, and CL1518 are discontinued.

Note:CL3715, CL3721, CL3722, CL3725,CL1517, and CL1518 are discontinued.

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About the student

Prerequisites

Basic understanding of telecommunication and basic engineering math concepts.

Audience

Engineers in need of an in-depth understanding of the CDMA air-interface technology and CDMA concepts for IS-95 (2G), IS-2000 (3G-1X), IS-856 (1xEV-DO), and who will continue taking other courses in the wireless CDMA engineering curriculum.

Class size

The class size for the instructor-led version is a minimum of 12 students, and a maximum of 20 students.

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End-of-course assessment

Introduction

This course uses Level 2 Assessment tools to gauge the extent to which you have met the objectives of the course. Level 2 Assessment results should be used solely to make further training and development decisions. The results may not be used for any other purpose without the written consent of Lucent Technologies Information Products & Training.

Purpose of the assessment

As stated above, the assessment serves a developmental purpose. There are a number of benefits to having the assessment as part of this course.

Use of the Level 2 Assessment will objectively measure effective training. The questions are linked to the course objectives, which, in turn, are linked to the tasks performed on the job. These links hold our course developers and instructors accountable to produce and deliver materials that are relevant to your needs.

Additional information

See the appendix for details on how to take the Level 2 Assessment.

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Contents

1. Fundamental Radio Concepts and CDMA Introduction

1.1: Electromagnetic waves

1.2: RF modulation

1.3: Why digital?

1.4: Digital signal modulation

1.5: FDMA, TDMA, CDMA

1.6: Why CDMA?

1.7: CDMA Channel

1.8: FDD vs. TDD

1.9: Coherent vs. non-coherent demodulation

1.10: Some CDMA terms

1.11: Standards' relationships

1.12: OSI model

2. Spreading & Despreading

2.1: Spread spectrum techniques

2.2: Direct sequence spreading

2.3: Direct sequence despreading

2.4: Integrate & dump

2.5: Detection with noise

2.6: Eb/Nt explained

2.7: Noise rise

2.8: End-to-end overview

3. Information Coding

3.1: Typical signal processing

3.2: Speech encoding

3.3: Frames and quality indicator

3.4: Forward error correction

3.5: Bit interleaving

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4. CDMA Codes

4.1: Typical signal processing

4.2: Code correlation

4.3: CDMA codes

4.4: Long code

4.5: Short codes

4.6: Walsh codes

4.7: Scrambling & spreading

4.8: Digital modulation

4.9: Receiver

5. CDMA Concepts

5.1: RF impairments

5.2: Rake receiver

5.3: CDMA call processing overview

5.4: Random access

5.5: Soft handoff

5.6: Power control

5.7: Noise rise vs. coverage reduction

6. IS-95 Specifics

6.1: Major characteristics

6.2: Forward link channels

6.3: Forward link coding

6.4: Forward link CDMA codes

6.5: Reverse link channels

6.6: Reverse link coding

6.7: Reverse link CDMA codes

6.8: Primary and signaling traffic

7. IS-2000 Specifics








7.8: Reverse access specifics

7.9: Handoff specifics

7.10: Power control specifics

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8. IS-856 Specifics








8.8: Handoff specifics

8.9: Power control specifics

8.10: Pole point specifics

Appendix

Additional coding information

Web-based end-of-course assessment job-aid

Glossary

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About the course contents

Study plan

The lessons to study depend on the technology of interest. Lessons 1 through 5 cover the CDMA technology in general. Lessons 6, 7, and 8, cover IS-95, IS-2000, and IS-856, respectively.

Depending on the technology of interest, study the following lessons:

•IS-95 (a.k.a. 2G)

Lessons 1 through 5 are required

Lesson 6 is required

Lesson 7 is optional

Lesson 8 is optional.

•IS-2000 (a.k.a. CDMA2000, 3G-1X)


Lesson 6 is recommended

Lesson 7 is required

Lesson 8 is recommended.

•IS-856 (a.k.a. 1xEV-DO)




Lesson 8 is required.

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Notes:

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Notes:

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Notes:

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Lesson 1Fundamental Radio Concepts

and CDMA Introduction

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Lesson Objectives

• Explain the benefits of digital transmission• Differentiate CDMA from FDMA and TDMA• Explain the benefits of CDMA• Illustrate the relationship between IS-95, IS-2000, and IS-

856.

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1.1 Electromagnetic Waves

• Electromagnetic waves propagate better than sound– Radio frequencies (30 kHz – 30 GHz) used in cellular

– Signal described asy(t) = A * sin(2π * f * t + φ)

• Modulation allows another signal to be transported by the RF signal.

0

A

1 / f

φt

Speech, or more specifically sounds that humans can hear (20 Hz - 20 kHz), propagates by pushing air molecules around. Therefore, sound loses its energy relatively quickly and is limited in propagation over distance. Electromagnetic waves, on the other hand, can travel a much larger distance.

The Scottish scientist James Clark Maxwell, in 1864, predicted the possibility of propagation of electromagnetic waves. The theory was based on work done by Michael Faraday. It was a German scientist, Heinrich Hertz, who was able to prove Maxwell’s theory through a series of experiments between 1886 and 1888.

The basic idea is to couple electromagnetic energy into a propagation medium by means of a radiation element such as an antenna. The frequency, or wavelength (λ), of the electromagnetic wave impacts the wave’s capability of propagation. Lower frequency waves, or longer wavelength, tend to follow the earth’s surface and is reflected and refracted by the ionosphere (part of the earth’s atmosphere about 60 km above the surface). Above about 300 MHz, the electromagnetic waves propagate by means of line-of-sight, and somewhere above 1000 GHz, the waves become optical in character.

Radio frequencies (RF) generally refers to frequencies from 30 kHz to 30 GHz. RF is used in cellular communication and is assumed throughout this course.

The RF signal, y(t), is assumed to be a sinusoidal signal with amplitude A, frequency f, and phase φ. The frequency is often expressed in radians, ω, where ω = 2π*f.

y(t) = A * sin(2π * f * t + φ)

The main frequency, or center frequency, is called carrier frequency, or the carrier. The carrier frequency should be much greater than the effective bandwidth of the information signal.

Since RF signals are so much better than sound to propagate (travel), we want to use the RF signals to carry our desired information. The process of making an RF signal carry specific information (another signal) is called modulation.

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1.2 RF Modulation

• Amplitude Modulation (AM)– A(t) * sin(2π * f * t + φ)– Simple implementation

– Sensitive to noise

• Frequency Modulation (FM)– A * sin(2π * f(t) * t + φ)– More robust against noise

• Phase Modulation (PM)– A * sin(2π * f * t + φ(t))– Similar to FM.

Given the sinusoidal signal, y(t) = A * sin(2π * f * t + φ), there are three parameters that can be adjusted, or modulated, with the original signal, m(t), that is to be transmitted. The three parameters are amplitude (A), frequency (f), and phase (φ).

Amplitude Modulation (AM)

When the information signal, m(t), modulates the amplitude of the carrier, we call this modulation technique for Amplitude Modulation (AM).

The benefit of AM is the simplicity with which it can be demodulated. One inexpensive demodulation method is called envelope detection. One drawback with AM is that the signal can easily be degraded by noise or interference.

Frequency Modulation (FM)

When the information signal, m(t), modulates the frequency of the carrier, we call this modulation technique for Frequency Modulation (FM).

FM requires a more sophisticated demodulator which can detect frequency deviation. However, a big advantage of FM over AM is that FM is less susceptible to noise.

Phase Modulation (PM)

When the information signal, m(t), modulates the phase of the carrier, we call this modulation technique for Phase Modulation (PM).

Since both the frequency and phase parameters are impacting the sin(…) operation, PM is similar to FM. See the figure. Therefore, PM and FM have similar characteristics.

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1.3 Why Digital?

• Analog signals are easilydistorted by noise

• Analog signals can be represented in a digital form– Nyquist criterion

• Digital signals can sustain morenoise than analog

• Additional information canbe included in the bit stream.

In 1928, Harry Nyquist published his famous sampling theory. The sampling theory, the Nyquistcriterion, states that an analog signal can be completely reconstructed from a set of uniformly spaced discrete-time samples, if the sampling rate is equal to or greater than the bandwidth of the signal.

Analog vs. Noise

Analog signals are more susceptible to noise than digital signals. The quality (or correctness) of an analog signal depends on how exactly the receiver can detect the envelope, or curve, or the signal. Shown in the figure is an analog signal with noise added; the correct signal is also shown. When noise is added to an analog signal, the instantaneous envelope value can vary significantly from the actual envelope, thereby degrading the quality of the signal.

Digital vs. Noise

When transmitting a digital signal, only ones and zeroes must be detected. The detection can be done using a maximum likelihood decoder. For example, assume that a digital ‘1’ is represented as a -1 voltage, and a digital ‘0’ is represented as a +1 voltage. When decoding, the maximum likelihood detector can determine the received bit to be ‘1’ if the received voltage is less than 0, and a ‘0’ is the voltage is greater than 0.

One can easily see that a digital signal can sustain more noise than an analog signal and still yield the correct information bit in the receiver without any degradation in quality.

Other Benefits of Digital

With digital transmission schemes come all the advantages that traditional microprocessor circuits have over their analog counterparts. Any shortfalls in the communications link can be eradicated using software. Information can now be encrypted, and error correction can ensure more confidence in received data. Also, additional information can be included in the data stream.

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1.4 Digital Signal Modulation

• Amplitude Shift Keying (ASK)– On-Off Keying

– Rarely used today

• Frequency Shift Keying (FSK)– Two distinct frequencies

transmitted

• Phase Shift Keying (PSK)– Phase of signal is changed

– Several phase changes possible• QPSK.

When transmitting digital signals, variations of AM, FM, and PM schemes are used. The digital signal modulation schemes are often called Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK). As with FM and PM, FSK and PSK offer more immunity to noise, and are the preferred schemes today.

Amplitude Shift Keying (ASK)

Since ones and zeroes are transmitted, ASK transmits a signal with a given amplitude for one bit value, and little or no amplitude for the other bit value. Early telegraphy used ASK to transmit Morse code, but today pure ASK is rarely used.

Frequency Shift Keying (FSK)

A simple variation from traditional analog FM can be implemented by applying a digital signal to the modulation input. Thus, the output takes the form of a sine wave at two distinct frequencies. To demodulate this waveform, it is a simple matter of passing the signal through two filters and translating the resultant back into logic levels.

Phase Shift Keying (PSK)

PSK involves changing the phase of the transmitted waveform instead of the frequency. In its simplest form, a PSK waveform can be generated by using the digital data to switch between two signals of equal frequency but opposing phase (Binary PSK, BPSK). If the resultant waveform is multiplied by a sinusoidal wave of equal frequency, two components are generated: one cosine waveform of double the received frequency and one frequency-independent term whose amplitude is proportional to the cosine of the phase shift. Thus, filtering out the higher-frequency term yields the original modulating data prior to transmission. This is difficult to picture conceptually, but a mathematical proof can be done.

Quadrature Phase Shift Keying (QPSK)

Taking the above concept of PSK a stage further, it can be assumed that the number of phase shifts is not limited to only two states but multiple states. The transmitted carrier can undergo any number of phase changes and, by multiplying the received signal by a sine wave of equal frequency, will demodulate the phase shifts into frequency-independent voltage levels.

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1.5 FDMA, TDMA, CDMA

• Frequency Division Multiple Access (FDMA)– Divides bandwidth B into N channels

– Supports N users

• Time Division Multiple Access (TDMA)– Uses FDMA and timeslots– Divide B into N channels and TS timeslots

– Supports N * TS users

• Code Division Multiple Access (CDMA)– Uses entire bandwidth, BC, for all users

– Supports a dynamic number of users.

Bandwidth

U1

U2

U3B

t

Bandwidth

U1

U3

U5B

t

Bandwidth

BC

t

U2

U4

U6

U1

U3

U5

U2

U4

U6

Cellular systems rely on RF as the primary means of communication between the mobile station and the base station. In an ideal world, there is an unlimited frequency spectrum available. In our world, though, there is not unlimited frequency spectrum because a certain amount of the accessible frequency spectrum has been allocated for commercial and non-commercial applications, such as AM/FM radio, TV broadcast, navigation systems, etc.

To access the limited frequency spectrum in a cellular system, several access techniques exists. The most common techniques include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA).

Frequency Division Multiple Access (FDMA)

With FDMA, the available frequency bandwidth, B, is divided into N number of channels, each with a bandwidth of BN (typically 30 kHz). Each active user is then assigned one channel. In other words, N users can be supported.

The total number of users supported in a system can be increased by implementing a frequency reuse plan – the channels are reused in areas some distance away.

Time Division Multiple Access (TDMA)

With TDMA, the available frequency bandwidth, B, is divided into N number of channels, each with a bandwidth of BN (typically 30 kHz for IS-136, and 200 kHz for GSM). In addition, each channel is divided into TS number of time slots (3 useable for IS-136, 8 for GSM). Each active user is then assigned a channel and a time slot. In other words, N*TS users can be supported.

The total capacity can be increased with a frequency reuse plan.

Code Division Multiple Access (CDMA)

With CDMA, a large bandwidth, BC, is dedicated to one CDMA Channel. BC is typically 1-5 MHz, depending on technology. An active user is assigned a unique code within the CDMA Channel. Using the unique code, the receiver can extract the specific user information from the CDMA Channel. The supported capacity is dynamic and a function of interference levels.

A frequency reuse plan is not needed in a CDMA system.

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1.6 Why CDMA?

• High and dynamic capacity– Same RF carrier frequency used in all sectors and all cells

• Enhanced RF channel performance– Rake receiver

– Soft handoff

• No interruption of traffic channel when using soft handoff• Soft blocking

– Determined by quality objective

• Longer battery life for mobile station• Lower transmission power levels• Inherent privacy.

One of the main benefits of CDMA is the dynamic capacity inherent in the technology. As will be shown later, capacity is a function of the interference levels in the system. By optimizing the system and the hardware and software of the network components, system capacity can be increased. In CDMA, coverage, capacity, and quality are related to each other, and one cannot increase one without sacrificing one of the other.

Compared to other technologies such as GSM and IS-136 (“TDMA”), the performance of CDMA is enhanced through Rake receivers and soft handoff. Rake receivers allow the receiver to efficiently combat multipath. Soft handoff allows the mobile station to have a seamless connection to the network without any interruptions as the mobile station moves around within the system.

By transmitting digital information and using effective coding techniques, the transmission power levels for a mobile station is lowered. This not only results in lower interference in the system, but also a longer battery life for the mobile station.

There is a degree of privacy inherent in the CDMA technology. By the use of pseudo-noise codes, an eavesdropper cannot intercept the information without extensive code-breaking computations. Please note that while there is inherent privacy in CDMA, the information is not encrypted. Encryption must be performed prior to the CDMA processing.

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1.7 CDMA Channel

• One CDMA Channel

• Multiple CDMA Channels

fc

3dB Bandwidth

Guard bandGuard band

fc1

3dB Bandwidth

Guard bandGuard bandfc2

3dB Bandwidth

Channel spacing

The 3 dB bandwidth of a channel is the frequency range where the signal at the edges is 3 dB lower than the peak value at the center frequency, fc. The center frequency is used to specify where in the frequency spectrum the CDMA Channel is located.

A CDMA Channel, or carrier frequency, has a 3 dB bandwidth of 1.23 MHz for IS-95 and IS-856. For IS-2000, the 3 dB bandwidth is 1.23 MHz or 3.69 MHz, depending on configuration (see IS-2000 Specifics lesson for details).

In addition to the frequency spectrum required for the CDMA Channel’s 3 dB bandwidth, frequency guard bands are also needed on each side of the channel if the CDMA Channel borders to spectrum not used for CDMA. The performance standard specifications recommend frequency guard band distance (bandwidth) for various frequency bands; e.g., IS-97 defines performance specifications for IS-95 and IS-2000 base stations, IS-864 defines the performance specifications for IS-856 base stations.

For adjacent CDMA Channels, no frequency guard band is needed between the CDMA Channels. Obviously, the CDMA Channels have to be spaced at least 1.23 MHz (or 3.69 MHz) apart. The frequency distance between two CDMA Channels is referred to as channel spacing. The channel spacing used depends on the channel numbering scheme for the particular frequency band. For example, in the 850 MHz spectrum (band class 0), the channel spacing is 1.23 MHz, while in the 1900 MHz spectrum (band class 1), the channel spacing is 1.25 MHz.

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1.8 FDD vs. TDD

• Frequency Division Duplex (FDD)– Most common

– Simple implementation

– May not be spectrum efficient withasymmetrical data links

• Time Division Duplex (TDD)– Efficient use of spectrum

– Requires precise synchronization andtiming.

Spectrum

Reverse link

Guard band

Forward link

t

Gu

ard

tim

e

Fo

rwar

d li

nk

Spectrum

Rev

erse

lin

k

Gu

ard

tim

e

Fo

rwar

d li

nk

t

In order to support duplex operation (simultaneous or pseudo-simultaneous communication between mobile station and base station) in a CDMA system, one of two techniques are often used: Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

Frequency Division Duplex (FDD)

The FDD scheme is the most common scheme. For every CDMA Channel, there is a forward link (base station to mobile station) CDMA Channel and a reverse link (mobile station to base station) CDMA Channel. This means that if the CDMA Channel is 1.23 MHz wide, then twice that spectrum is needed for FDD. See the figure.

Between the forward link and reverse link portions of the spectrum, there is a guard band to help isolate the receive part from the transmit part of the mobile station (or base station).

FDD is simple to implement. However, for data transmission where the data capacity requirements (and therefore often spectrum demand) are asymmetrical (often higher on the forward link), FDD may not efficiently use the total spectrum.

Time Division Duplex (TDD)

Instead of dividing the frequency spectrum between the forward and reverse links, the spectrum can be divided in time for the forward and reverse links. In other words, the available frequency spectrum is used for forward link transmission for some time period. During another time period, the same frequency spectrum is used for reverse link transmission. Between each transmission period, there is a guard period to help isolate forward and reverse link transmissions from each other.

TDD required precisely controlled synchronization and timing between forward and reverse link transmission. Therefore, the complexity of the system increases. The benefit of TDD is a more efficient use of the available frequency spectrum when asymmetrical capacity demands are experienced on the RF link. A longer time period for transmission can be assigned to, for example, the forward link. TDD also allows a CDMA Channel to be implemented in a very limited frequency spectrum.

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1.9 Coherent vs. Non-coherent Demodulation

• With coherent demodulation a phase reference is provided– Pilot Channel

– Phase changes can beanticipated

– Lower signal energy forinformation channel

• Non-coherent demodulation operates without a phase reference– Phase has to be guessed

– Higher signal energy needed.Phase

discrepancy

Real phase of signalPhase reference at receiver

The Federal Standard 1037C defines coherent as “pertaining to a fixed phase relationship between corresponding points on an electromagnetic wave.” This means that if the receiver has a phase reference available when demodulating the received information, coherent demodulation is performed. The phase reference in a CDMA system is provided by a Pilot Channel. The Pilot Channel is easy to detect because it has a simple code and relatively high signal energy.

When a Pilot Channel is present, the receiver can observe the changes in the Pilot Channel (e.g., phase) and anticipate the changes to the information channel.

If a Pilot Channel is not present, the receiver must perform non-coherent demodulation. Non-coherent demodulation means that the receiver must assume and guess the changes of the information channel. This typically means that the information channel requires much more power (theoretically 3 dB) than it would need if the Pilot Channel was present. The higher power is needed to minimize the phase discrepancy between the signal and the phase used in the demodulator.

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1.10 Some CDMA Terms

• User devices– Mobile station

– Access terminal (AT)

• 2G– IS-95

• cdmaOne

• 3G– IS-2000

• CDMA2000

• 1xRTT, 3xRTT

• 3G-1X, 3G-3X

– IS-856• 1xEV-DO.

There are a number of terms in CDMA that may be confusing to the reader. The confusion may stem from the fact that different terms often describes the same, or similar, components, concepts, etc. A lot of terms will be described and explained throughout this course. Here, a few of the frequently seen terms will be explained.

The network component being used when accessing the system is often called a mobile station (MS), or simply mobile. For IS-856, the same mobile station is called an access terminal (AT). AT is only used exclusively in the IS-856 Specifics lesson. In other lessons where mobile station is used, the information also applies to an AT.

When discussing the technologies covered in this course, various terms may be used. The terms can perhaps be classified as second generation (2G) terms and third generation (3G) terms.

IS-95 specifies the air-interface used for the 2G CDMA system branded as cdmaOne. For the 3G air-interface, two specifications are discussed in this course: IS-2000 and IS-856.

IS-2000 is one of the radio transmission technologies (RTT) used for 3G systems; hence, 1xRTT and 3xRTT for the two configurations of IS-2000. See the IS-2000 Specifics lesson for details regarding the two configurations. Similar to IS-95 and cdmaOne, the IS-2000 based system is called CDMA2000, and sometimes CDMA2000-1X and CDMA2000-3X.

Lucent Technologies often refers to the IS-2000 system as 3G-1X or 3G-3X.

IS-856 is an evolution of IS-2000, but is used for data applications only. The IS-856 system is also called 1xEV-DO, CDMA2000-1X EVolution Data Only.

For other terms found throughout this course, please refer to the glossary.

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What is 3G?

• ITU’s IMT-2000– Global roaming

– High data rates• Variable

• Negotiable (QoS)

• Asymmetrical

– Internet connectivity• E-mail push

– Support for multimedia services

• IS-2000 and IS-856 are approved IMT-2000 specifications.

Global

RegionalLocal Area

IndoorOffice/Home

MEGA CELL

MACRO CELL

MICRO CELL

PICO CELL

> 9.6 kb/s

> 144 kb/s

> 384 kb/s

> 2.048 Mb/s

89

7

45

6

32

1

#0

*

The International Telecommunication Union (ITU) envisioned one unifying terrestrial air and core network system for the “next generation” of wireless communication, a.k.a. 3G. ITU’s recommendations for the “next generation” systems are called International Mobile Telecommunications-2000 (IMT-2000). Some of the major aspects of IMT-2000 include:

•Global roaming that would allow a mobile user from anywhere in the world to expect the same standard set of wireless services and features, regardless of where the user travels and the country visited

•High data rates optimized for different terrestrial radio environments:

– Global satellite (megacell) environment, minimum 9.6 kbps

– High mobility, vehicular (macrocell) environment, minimum 144 kbps

– Low-mobility, pedestrian (microcell) environment, minimum 384 kbps

– Indoor (picocell) environment, minimum 2 Mbps

•Internet connectivity and services comparable with direct landline connection. Also supporting asymmetric (data rate) links and e-mail push; user does not have to connect to system to receive e-mail

•Negotiable quality of service (QoS) allowing the user to negotiate the QoS with regard to data rate, bit error rate, and latency

•Variable data rates, allowing the user to get a higher data rate when the system is less busy

•Support of multimedia services such as streaming video.

Two specifications classified by the ITU as 3G technologies are discussed in this course, IS-2000 and IS-856. IS-95 is not classified as a 3G technology.

Rajesh Choudhary

Highlight

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1.11 Standards’ Relationships

• IS-95A– Original CDMA cellular

technology

– Voice and low speed data (14.4 kbps)

• IS-95B– Enhanced performance

– Voice and medium speed data (115.2 kbps)

• IS-2000– Increased capacity,

scalability

– Voice and high speed data (1,036.8 kbps)

• IS-856– IP network

– High speed data only (2,457.6 kbps)

Backwardcompatible

Backw

ard

compatib

le

RFcompatible

IS-95 revision A, IS-95A, was the first commercial implementation of the CDMA technology as a wireless communication system. Published in 1993, the standard specification became very popular, especially in North America. IS-95A supports voice and low speed data applications with a maximum data rate of 14.4 kbps.

IS-95 was revised to revision B, IS-95B, in early 1999. IS-95B improved the performance of the CDMA systems by adding and enhancing existing algorithms and parameters. Medium speed data, up to 115.2 kbps, is also supported in IS-95B. Few networks were deployed using IS-95B, due to the emerge of third generation (3G) technologies.

No further revisions of IS-95 were made. The work focused instead on IS-2000 (“IS-95C”) with a more timely numbering scheme. Revision A of IS-2000 was released in early 2000. Several technology enhancements were made in IS-2000 that dramatically increased voice capacity compared to IS-95 while still maintaining backward compatibility. True high speed data was also implemented with data rates up to 1,036.8 kbps. More common data rates seen are data rates up to 307.2 kbps. With the use of two different RF carrier bandwidths and additional channels, IS-2000 proves to be more scalable than IS-95.

In early 2002, IS-856 was published. IS-856 is based on IS-2000, but removes voice-capability and focuses on data only operation. By focusing on data only operation, the data rate for an IS-856 system can reach 2,457.6 kbps. Another noticeable difference between IS-856 and IS-2000 is that IS-856 is an IP-based network, whereas IS-2000 relies on proprietary protocols. IS-856 is backward-compatible with IS-2000 at the RF level. This means that RF components can be shared between the two systems.

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Data Implementation

• IS-95A– Regular Traffic Channel can carry up to 14.4 kbps with vocoder

bypass

• IS-95B– Traffic Channel consists of a FCCH and optional SCCH– FCCH and aggregated SCCH can carry up to 115.2 kbps

• IS-2000– Supplemental Channel carries up to 1,036.8 kbps– Efficient interference control

• IS-856– Forward link Data Channel carries up to 2,457.6 kbps

• Time-multiplexed between users• One user gets all the resources based on scheduling algorithm

– Reverse link Data Channel carries up to 153.6 kbps.

IS-95 and IS-2000 supports voice in the system. The implementation of the voice application is the same between the two technologies. IS-856 is a data only technology. All the technologies, IS-95A, IS-95B, IS-2000, and IS-856, support data. The technology specific lessons further discuss the implementation of data.

IS-95A

Data rates up to 14.4 kbps are supported in revision A of IS-95, using the Traffic Channel. This is achieved by bypassing the vocoder (processing the speech for transmission).

IS-95B

Revision B of IS-95 introduced two sub-channels of the Traffic Channel: the Fundamental Code Channel (FCCH) and Supplemental Code Channel (SCCH). The FCCH supports voice and low speed data rates up to 14.4 kbps. Higher data rates are achieved by aggregating up to seven SCCHs. The maximum data rate for IS-95B is 115.2 kbps

IS-2000

In IS-2000, the Supplemental Channel is introduced. The Supplemental Channel is used for data traffic only, and can carry up to 1,036.8 kbps, depending on the current configuration.

IS-2000 also introduced the ability to efficiently control interference generated in the system due to the high speed data traffic.

IS-856

The forward link in IS-856 can carry data rates up to 2,457.6 kbps. This is achieved bymultiplexing the forward link resources between the users. When time-multiplexing is used, all the forward link resources can be concentrated to one user, and the data rate maximized. The user who will received the forward link Data Channel is determined by a scheduling algorithm.

The reverse link Data Channel carries up to 153.6 kbps.

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1.12 OSI Model

OSIApplication (Layer7)

Presentation (Layer6)

Session (Layer 5)

Transport (Layer 4)

Network (Layer 3)

Data Link (Layer 2)

Physical (Layer 1)

The Open System Interconnection (OSI) model was developed in 1984 by the International Standardization Organization (ISO). It specifies a seven-layer model which is used by the industry as the frame of reference when describing protocol architectures and functional characteristics. The seven layers are application, presentation, session, transport, network, data link, and physical layers. To remember the layers, the following sentence could be used: ”All People Seem To Need Data Processing.”

•Layer 7: The application layer supports application and end-user processes. This layer provides application services for file transfers, e-mail, etc.

•Layer 6: The presentation layer formats data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

•Layer 5: The session layer establishes, manages, and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end.

•Layer 4: The transport layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

•Layer 3: The network layer provides switching and routing technologies, creating logical paths known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control, and packet sequencing.

•Layer 2: The data link layer furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control, and frame synchronization.

•Layer 1: The physical layer conveys the bit stream - electrical impulse, light or radio signal -through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining channels and cables (if wireline).

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OSI Model vs. CDMA

OSI TCP / IP

Application (Layer7)Application

Presentation (Layer6)

Session (Layer 5)

Transport (Layer 4) Transport (TCP)

Network (Layer 3) Internet (IP)

Data Link (Layer 2)Network Access

Physical (Layer 1)

CDMA RadioAccess Network

For voice applications, the OSI model has not been much of a concern since each voice user is similar from a resource (RF, hardware, etc.) point of view. However, for data applications, different users may use different applications. Each application may have significantly different resource demands. Therefore, it is important to structure the system in order to manage the information.

Most data applications are based on an IP network. From an RF point of view, in an IP network the CDMA radio access network (RAN) operates in the first three layers of the OSI model, Layers 1-3, supporting IP traffic. While the RAN may operate within the first three OSI layers to support the IP network, the RAN may have its own internal layers resembling the OSI model (e.g., IS-856).

Obviously, following the OSI model is not required for a communication system to function properly.

In this course, the focus will be on Layer 1, the physical layer.

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Summary

• RF carrier is modulated with a digital signal– ASK

– FSK

– PSK

• Digital is more robust against noise• CDMA is a preferred access method over FDMA/TDMA

– Dynamic capacity

– Enhanced RF performance

– Inherent privacy

• The physical layer will be covered in this course– IS-95 (cdmaOne)– IS-2000 (CDMA2000, 3G-1X, 3G-3X)

– IS-856 (1xEV-DO).

RF frequencies are generally referred to as the electro magneticwaves propagating in the frequency range of 30 kHz to 30 GHz. Using various modulation techniques, and information signal can be carried by an RF signal (carrier frequency). Several modulation techniques for a digital information signal exist, e.g., ASK, FSK, and PSK. Digital transmission is preferred over analog transmission since a digital signal can sustain more noise and, at the same time, implement error correction schemes.

With a limited frequency spectrum and multiple users, an access method must be selected to accommodate the users. Out of the three access methods described (FDMA, TDMA, and CDMA), CDMA is preferred due to its dynamic capacity, enhanced RF performance (Rake receiver and soft handoff), and inherent privacy. The capacity is dynamic because the same RF carrier frequency is used across the network. Multiple CDMA carriers can co-exist within a network, provided that they are separated in frequency (channel spacing) and do not have overlapping 3 dB bandwidths (1.23 MHz or 3.69 MHz).

Three CDMA air-interface technologies are discussed in this course, IS-95 (cdmaOne), IS-2000 (CDMA2000, 3G-1X, or 3G-3X), and IS-856 (1xEV-DO). Of the three technologies, IS-2000 and IS-856 are approved 3G technologies according to the ITU. IS-2000 is backward-compatible with IS-95. IS-856 is an evolution of IS-2000, with data only capability.

This course focuses on the air-interface specifications of the technologies discussed. The air-interface is the physical layer (Layer 1) of the OSI model.

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Knowledge Check

1. Why is digital transmission more beneficial than analog transmission?A. More noise can be sustained without degrading quality

B. Error correction can be implemented to further improve the signal

C. Battery life is increased for the mobile station

D. Any of the above

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Knowledge Check – cont’d

2. What uniquely identifies a TDMA user channel?A. Channel number only

B. Time slot and unique code

C. Channel number and time slot

D. Channel number and unique code

3. What uniquely identifies a CDMA user channel?A. Channel number only

B. Time slot and unique code

C. Channel number and time slotD. Channel number and unique code

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4. What is one of the benefits of CDMA?A. A fixed, high capacity

B. Enhanced RF performance

C. Increased capacity using a frequency reuse plan

D. Any of the above

5. For a typical CDMA carrier, what is the minimum required channel spacing?A. 1.23 MHz

B. 1.25 MHzC. 2.5 MHz

D. 5 MHz

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6. Match the following terms:A. Mobile station 1. 1xEV-DO

B. IS-95 2. Access terminal

C. IS-2000 3. 3G-1X

D. IS-856 4. cdmaOne

7. IS-856 can share certain RF components with IS-95A.A. True

B. False

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8. An IS-95 mobile station may be able to make a call on a IS-2000 network.A. True

B. False

9. An IS-856 access terminal may be able to make a call on a IS-2000 network.A. True

B. False

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Lesson 2Spreading & Despreading

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Lesson Objectives

• Explain Direct Sequence spreading and despreading• Describe processing gain• Explain Eb/Nt

• Explain noise rise.

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2.1 Spread Spectrum Techniques

• Spread spectrum theory created by actress Hedy Lamarr– Would be used to guide submarine torpedoes to German targets

during World War II

– Military applications did not appear until 1962

• Different types of spread spectrum techniques– Frequency Hopping (FH)

– Time Hopping (TH)– Direct Sequence (DS)

• In this course, CDMA implies DS spread spectrum.

Frequency

U1

U2

U3

t

Frequency

t

Frequency

U1 U2U3

t

U1

U1

U1

U2

U2

U3

U3

U3

U2U1 U2U3

FH TH DS

Spread Spectrum History

Spread spectrum theory dates back to a Hollywood party in 1940 and a conversation between Austrian actress Hedy Lamarr and composer George Antheil. Prior to coming to the United States, Hedy Lamarr had been married to an Austrian arms dealer who dealt willingly with Hitler’s Nazis and frequently brought his clients home for dinner and business discussions. Although she was believed to be little more than window dressing, Lamarr’s husband would have been astonished to discover how much she learned from his dinner meetings.

Hedy Lamarr fled Austria before the outbreak of World War II and headed to Hollywood to resume her acting career. Desiring to contribute to the war effort, she explained her “Secret Communication System” theory to Antheil, who sketched and took notes. The theory was an electronic means of controlling torpedoes from a submarine to its target.

The “Secret Communication System” used synchronized paper tapes to perform frequency hopping to prevent guidance signals to the torpedo from being disrupted. The heart of the system was the synchronized paper tapes. These paper tapes would automatically change the frequency of the transmitter and receiver so that an enemy could not detect and lock onto the signal.

In 1942, Lamarr and Antheil patented their idea and offered it to the Navy for free. The Navy could not comprehend the concept and declined the offer. Neither Lamarr nor Antheil pursued the idea any further and the concept of spread spectrum was lost until it appeared in equipment used during the Cuban Missile Crisis in 1962. By then, the exclusive rights to the patent had expired and neither of its inventors received money for spread spectrum.

Spread Spectrum Techniques

The CDMA modulation technique uses three methods for spectrum spreading:

•Frequency Hopping (FH); transmission frequency appears random

•Time Hopping (TH); transmission time appears random

•Direct Sequence (DS); the transmitted signal appears random

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2.2 Direct Sequence Spreading

CDMARadioSignal

Information coder and

processingc(t)

Information Signal

Modulator

DS generator

Baseband CDMA Signaling

y(t)b(t)

b(t) 0

c(t) 0

y(t)= 0b(t) c(t)

1

1

1

-1

-1

-1

b(f)

fb

f

Tb

fc

f

y(f)

t

t

t

c(f)

fc

f

Tc

Introduction

CDMA uses a modulation technique called “spread spectrum” to transport a narrowband voice signal over a wide bandwidth channel. The wide bandwidth for IS-2000 is 1.23 MHz.

The CDMA modulation technique uses three methods for spectrum spreading:

•FH (Frequency Hopping)

•TH (Time Hopping)

•DS (Direct Sequence).

Because Lucent systems operate only with DS spreading, it is the only spreading technique discussed throughout the remainder of this course, so whenever CDMA is mentioned, DS CDMA is implied.

Spreading

In a spread spectrum system, the data information signal, b(t), is multiplied by a wideband signal, c(t), which is the output signal of the Direct Sequence (DS) generator: A pseudorandom noise (PN) output signal. The signal which will eventually be transmitted, y(t)=b(t)c(t), will occupy bandwidth far in excess of the minimum bandwidth to transmit the data information.

Note that Tb is the bit interval of the information stream, and Tc is the bit interval of the DS stream. Tc is also called a chip time. It should also be noted that the ratio of Tb to Tc is referred to as the processing gain.

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Signal Spreading

With c(t) faster:

t

t

c(t)

1

-1

1

-1

b(t)Tb

1

-1

b(t) c(t) t

Tc

Inverse InverseSame

Period Tb

BWb =1Tb

Period Tc

BWc =1Tc

Period Tc

BWc > BWb

1Tc

=

BitsBits

ChipsChips

Spreading

When two signals, b(t) and c(t), are multiplied together, the resulting signal, b(t)c(t), will have the same bit (or chip) period as the faster signal (wider bandwidth); in this case, c(t). The signal b(t) can be seen as altering the phase of the spreading signal c(t).

Observe that the combined signal waveform shown has more high frequency changes than the changes in the data information since (1/Tc) >> (1/Tb). Note that Tb is the bit interval of the information stream, and Tc is the bit interval of the DS stream. Tc is also called a chip time.

When c(t) is faster, y(t) contains all the information of b(t), and has the faster bit rate and its correspondingly wider spectrum. In addition to being scrambled, b(t) is said to have had its spectrum spread.

Scrambling

When b(t) and c(t) have the same rate, the product y(t)=b(t)c(t) contains all the information of b(t) and has the same rate. The spectrum of the signal is unchanged, and the incoming bit stream is said to be encrypted or scrambled.

Bit and Chips

In CDMA, the terms chips and bits are often used. The terms “chips” and “bits” both refer to ones and zeroes, but they have slightly different meaning. When talking about the digital signal that is spread over a wide bandwith signal, b(t) in the example, the ones and zeroes are typically called “bits.” The ones and zeroes of the digital signal that is being used to spread the information signal, c(t) in the example, are typically called “chips.”

So, what happens in the spreading process is that when a bit is +1 the chips remain the same, but when a bit is –1, the chips change their polarity, and we “flip the chips.”

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2.3 Direct Sequence Despreading

. . .c(t)

b(t) c(t)

c(t)

b(t)b(t) c(t)

t

output= b(t) c(t) c(t)= b(t)

b(t) 0

1

1

-1

-1

output = 0b(t) c(t) c(t)

= b(t)

c(t) 0

1

-1

b(t) c(t) 0

1

-1

. . . t

Waveforms

“0”

“1” . . .

“0”

“1”

. . . t

. . .

t

t

To despread a received signal, b(t)c(t), the signal is multiplied with an exact replica of the original spreading code, c(t). The output of the despreader will be b(t)c(t)c(t) = b(t).

Note that c(t)c(t)=+1 for all bits; this is true for any bipolar waveform encoded as +1, -1. Also, if signal propagation delays the output b(t)c(t) by some propagation time, the second occurrence of c(t) must be delayed by the same amount (synchronization!).

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Why It Works!

t

tc(t)

Receiver receives b(t)c(t), multiplies by c(t), resulting in b(t)c(t)c(t) = b(t).Multiplying with another code would not yield the same result

1

-1

0

c(t)c(t)

1

-1

0

0 01 0 1

The reason DS CDMA despreading works is seen by understanding that multiplying c(t) with itself produces +1 for all bits. Hence, c(t)c(t) is an identity operation producing b(t).

Note: One c(t) accompanies signal transmission and sees transmission delay. The other c(t) is inserted at the receiver with bit boundaries aligned to the first (i.e., synchronization).

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2.4 Integrate & Dump – Good Reception

b(t) 0

c(t) 0

y(t) = 0b(t) c(t)

1

1

1

-1

-1

-1

Tb

t

t

t

Tc

b’(t) = 0y(t) c(t)

1

-1

t

+1+1+1+1+1+16

bit1 = = +1.00

-1 -1 -1 -1 -1 -16bit2 = = -1.00

bit1 bit2

At the CDMA receiver, there is a process taking place that is often referred to as “integrate & dump.” Integrate & dump means that for the duration of the bit, after the received signal is multiplied with the spreading code, each individual chip value is summed up (integrate), a decision is made and reported, and the sum is reset to zero (dump) to be ready for the next bit.

The decision whether a bit is a +1 or a -1 can be made by saying that if the integration (sum) is greater than zero, then the bit is a +1; if it’s less than zero, it is a -1. The graphic illustrates the integrate and dump process when the received chip-stream is error-free.

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Integrate & Dump – Chip Errors

b(t) 0

c(t) 0

1

1

1

-1

-1

-1

Tb

t

t

t

Tc

1

-1

t

y(t) = 0b(t) c(t)

b’(t) = 0y(t) c(t)

+1+1+1 -1+1 -16

bit1 = = +0.33

-1 -1+1 -1 -1 -16bit2 = = -0.83

bit1 bit2

If the received chip-stream consists of chips in error, the bit may still be detected. As long as more than 50% of the chips per bit are error-free, the integrate & dump process will make a correct decision as to the bit-value. If a bit is received in error, higher level error-correction algorithms may detect and correct the bad bit.

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Linear Summation

• When transmitting multiple information signals at the same time, linear summation is used.– Every chip magnitude, voltage (electrical field strength), is

summed up.10

-1

10

-1

10

-1

3210

-1-2-3

ytot = y1+ y2+ y3

y3

y2

y1

When multiple information signals, or channels, are transmitted simultaneously, their bit streams are summarized together in a linear fashion. The graphic illustrates the concept by summarizing the three signals’ electrical field strengths to yield a composite bit stream with varying magnitude.

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Linear Summation – Exercise 1

• Use the codes below to calculate:– y1=b1*c1, y2=b2*c2, and y3=b3*c3

– There are six chips per bit

• Then, calculate the sum ytot=y1+y2+y3.10

-1b1

10

-1c1

10

-1b2

10

-1c2

10

-1b3

10

-1c3

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Linear Summation – Exercise 2

• Use ytot from previous exercise (#1) and multiply with c1, and integrate & dump to extract the bit values.– Sum > 0 means +1 (“0”), sum < 0 means -1 (“1”)

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2.5 Detection With Noise

1/Tb 1/Tc

f

Spectrum ofN(t) c(t)

Spectrum of b(t)

Filter F

. . .

N(t)

b(t) c(t)

c(t)

b(t)b(t) c(t) N(t) + b(t) c(t)

c(t)

d(t)F e(t)

Spreading Gain = G = Tc

Tb

d(t) = b(t) c(t) c(t) + N(t) c(t)= b(t) + N(t) c(t)

narrowband widebandEb

Nt

When the CDMA signal is transmitted it is exposed to noise, N(t), most notably from the RF environment. The receiver receives the original CDMA signal, b(t)c(t), plus an additive noise component, N(t).

When despreading the received signal the noise component will be, or continue to be, spread over the wide bandwidth spreading signal. If a low-pass filter is tuned to filter out everything except the narrowband signal, b(t), the result will be a signal with a certain bit energy, Eb, for b(t) and a narrowband noise component, filtered N(t)c(t), with an energy of NT (or N0). The signal to noise ratio is then Eb/NT or Eb/N0.

The result of the despreading is that the noise energy from the despreader is decreased, and it appears as if b(t) has experienced a gain, the so-called spreading gain, G = Tb/Tc.

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Spreading Gain

Transmitted BTS Power

f

User 1

User 2All users spread

Receiver output after despreadinguser 1

f

User 1User 2

(same power)

User 2 still spread

Filter

bw

BWFilter output

f

User 1

User 2Filter output = Puser1 + Puser2 X

same power

bwBW

PsignalPnoise

The S/N at test point is:bwBW

SN

= Puser1Puser2 x

= = G P1P2

BWbw Puser1

Puser2=

Note: Supressing noise by 1/G appears like signal is increased by G

Note: Supressing noise by 1/G appears like signal is increased by G

¤

Spreading gain or processing gain is achieved when noise components, or noise-like components, remain spread when the original signal (user 1 in the figure) is despread. The original signal appears to have gained energy relative the noise. It can also be seen as if the noise has been suppressed.

By filtering out most of the wideband noise energy the original signal can be extracted, provided sufficient bit energy over noise ratio, Eb/NT. It can be seen that the “signal to noise” ratio after despreading will favor user 1 by a factor of G = BW/bw (or Fc/Fb or Tb/Tc). G is then called spreading gain or processing gain. Processing gain can also be seen as the number of chips per bit.

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Quick Quiz

• What is processing/spreading gain?

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2.6 Eb/Nt Explained

1/Tb 1/Tc

f

Spectrum ofN(t) c(t)

Spectrum of b(t)

Filter F

Eb

Nt

After the received CDMA signal has been despread, the resulting signal consists of a relatively narrow-band information energy and a wide-band (suppressed) noise energy. When passing the despread signal through a low-pass filter, the majority of the noise energy is removed, and the resulting signal consists of a narrow-band information energy (Eb) and a narrow-band noise energy (Nt). The ratio between Eb and Nt (Eb/Nt) is one of the main quality indicators of a CDMA signal.

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• What is the difference between Eb/NT and Ec/I0?– Eb/NT is traffic channel bit energy over noise.

• Eb/N0 is often used.

– Ec/I0 is pilot channel chip (bit) energy over interference.

Eb/NT and Ec/I0

One of the most common questions when discussing CDMA engineering is: What is the difference between Eb/NT and Ec/I0?

Eb/NT and Ec/I0 both describe the ratio of energy per bit (1’s and 0’s) over interfering energy. The difference is in what channels we are referring to, and whether the discussion is about bits or chips.

Eb/NT is traffic channel bit energy over noise.

When talking about the digital signal that is spread over a wide bandwith signal, the 1’s and 0’s are typically called “bits.” The signal’s “signal-to-noise” ratio for the spread signal is often referred to as Eb/NT; hence, “traffic channel Eb/NT.”

The term Eb/N0 (pronounced “ebb-no”) is also used. In literature, N0 is often used for thermal noise or white noise; however, in CDMA, N0 and NT are used interchangeably.

Ec/I0 is pilot channel chip (bit) energy over interference.

The 1’s and 0’s of the digital signal that are being used to spread the information signal are typically called “chips.” The signal’s “signal-to-noise” ratio for the spreading signal is often referred to as Ec/I0. The pilot channel in a CDMA system is a non-spread signal (bandwidth 1.23 MHz); therefore, the term “pilot channel Ec/I0” is often used.

I0 normally refers to the interference level. Theoretically, the thermal noise (and other noise sources) impacts the Ec/I0 ratio. In a practical CDMA system, the generated interference energy is much greater than the thermal noise energy; therefore, the thermal noise may be ignored.

Note: It is important to understand that there is a difference between a CDMA RF carrier’s signal to noise ratio (S/N or S/I) and the digital CDMA signal’s Ec/I0.

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2.7 Noise Rise

Transmitted signal:I = Desired signaln = Other users the “noise” to user 1

After despreading:

Desired signal bandwidth = bwOther signals bandwidth = BW

andBWbw = 128 for 9.6 kbps (e.g. EVRC)

If signal power = 1, thennoise power / user = 1 X

bwBW = G-1

For n + 1 users, total voice power =nG

S/N = G/N

2 users S/N = 1

1/128 = 128

3 users S/N = 1

2/128 = 64

5 users S/N = 1

4/128 = 32

9 users S/N = 1

8/128 = 16

17 users S/N = 1

16/128 = 8

Quality relatedCapacity

Every user and channel in a CDMA system will have their own unique spreading code, c(t). Thus, if the receiver despreads and extracts the signal for user 1, all the other users (user 2, 3, …, M) will appear as “noise” or interference to user 1.

In other words, the more users there are on the CDMA system, the more “noise” the receiver experiences. This is called noise rise and is one of the core concepts of CDMA.

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Noise Rise vs. Loading

20

18

16

14

12

10

8

6

4

2

00 10 20 30 40 50 60 70 80 90

Percent Loading

NoiseRise(dB)

100

No

ise

Ris

e [d

B]

Reverse link loading or sector loading is a measure of the total interference from CDMA sources allowed in the system in reference to the receiver thermal noise. As the number of users in the system increases, the noise rise increases. The median noise rise in dB can be calculated as:

10log[ 1 / (1-loading) ]

where loading is a ratio of the number of active users to a theoretical maximum number of users, the pole capacity.

The noise rise increases dramatically as the loading approached the pole capacity. This noise rise is also driven by the loading of neighboring cells (frequency re-use efficiency) and the information data rate.

Since the goal is to maintain a certain communication link quality, Eb/NT, the noise rise (increased NT) impacts the CDMA coverage.

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2.8 End-To-End Overview

y(t)

1.2288 Mbps RF pathwith delay τ

Receive

c(t - τ)

b(t - τ)

codeddigital

informationdespreader

RegeneratedPN code

(1.2288 Mbps)

Mod

RFModulator

RF carrier

y(t - τ)

1.2288 Mbps

Transmit

c(t)

b(t)

codeddigital

informationspreader

PN code1.2288 Mbps

Demod

RFDemodulator

RegeneratedRF carrier

Transmit

Low bit rate speech, b(t), is spread by multiplying it with a high bit rate PN (pseudorandom noise) code, c(t).

The spread signal, b(t)c(t), is modulated by multiplication with an RF carrier and transmitted.

Receive

The received signal is delayed τ seconds and is demodulated by multiplication with the RF carrier.

The demodulated signal b(t-τ)c(t-τ), is despread by multiplication with the PN code, c(t-τ) to obtain b(t-τ)c(t-τ)c(t-τ) = b(t-τ).

The despread signal is detected by a bit detector (an integrate and dump lasting Tb seconds) to obtain the original digital speech.

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Summary

• When performing DS spreading, the information signal bit is multiplied with DS spreading code chips.– The DS spreading code should have pseudorandom noise

characteristics, orthogonal

– When several information signals are transmitted the output is alinear summation of all the chip.

• By despreading the received signal with the same DS spreading code, the information signal can be extracted.– Integrate & dump

– Information signals spread with other codes appear as noise, generating noise rise

• Processing gain is the number of chips per bit.• Eb/Nt indicates the quality of the information signal.

The spread spectrum theory was developed in the 1940’s. Several spread spectrum techniques exist. The technique discussed in this course is the direct sequence (DS) technique, where each information signal is spread using a spreading code. With orthogonal spreading codes with pseudo-random characteristics, several information signals can share the same spectrum. Multiple information signals are linearly summed for each chip.

At the receiving end, multiplying the transmitted signal with the exact same code used to spread an information signal will extract the original information signal. Other signals spread with other codes will appear as noise. The more noise an information signal experiences (loading), the higher the noise rise. The ratio (Eb/Nt) between the information signal’s bit energy (Eb) and the noise energy (Nt) indicates the quality of the signal.

A term often used with spread spectrum techniques is processing gain (spreading gain). Processing gain is an apparent gain that is introduced when a signal is despread. During depreading, only the information signal with the exact same spreading code is extracted; all other signals will become spread with that same code. After passing the despread signal through a low-pass filter, the noise energy level is suppressed; hence, it appears that the original information signal has gained energy.

Processing gain can be expressed as the number of spreading chips per information signal bit.

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Knowledge Check

1. Discussion: What is Eb/NT?

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2. Discussion: What is the difference between Eb/NT and Ec/I0?

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Knowledge Check

3. Why is there noise rise in a CDMA system?A. Users are using different RF carriers and different spreading

codes

B. Users are using the same RF carriers and the same spreading codes

C. Users are using different RF carriers but the same spreading codes

D. Users are using the same RF carriers but different spreading codes

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Lesson 3Information Coding

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Lesson Objectives

• Explain the concept of frames• Describe forward error correction• Explain bit interleaving.

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3.1 Typical Signal Processing

DigitalModulation

SpeechEncoding

RFModulation

QualityIndicator

FECEncoding

Interleaving

Scrambling Spreading

Information

Lesson 3

Lesson 4

Amp

CDMA Transmitter

Before the digital information signal can be transmitted in the RF environment it must undergo a number of signal processing steps. The general steps a transmitted signal undergoes is shown in the graphic. The steps are, but not limited to:

•Speech encoding. This step is only used if speech information is transmitted. Data transmission omits this step.

•Quality indicator

•Forward Error Correction (FEC) encoding

•Interleaving

•Scrambling

•Spreading

•Digital modulation

•RF modulation

•Amplification of RF signal.

Note: The various signal processing steps do not necessarily have to be performed in the order shown. Additional signal processing steps may also be taking place.

CDMA Receiver

At a CDMA receiver, similar steps take place but in the reverse order, i.e., first the received signal is demodulated, then de-spread, de-scrambled, de-interleaved, etc.

The various signal processing step shown will be discussed in more detail throughout the course.

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3.2 Speech Encoding

• A number of variable rate speech codersare supported using different service options.– EVRC most common

• Can be used for reducing facility costs by allowing speech to be packetized

• Vector Code-Excited Linear Predictive (VCELP) coder is used in CDMA.

95A 95B 3G 1xEV

In order to transmit speech over a digital system, it must be digitized and encoded using avocoder. Normal speech is received as an analog signal. The analog signal is converted into a digital signal using a process called Nyquist sampling, in which the analog input is typically sampled 8,000 times per second. The product of Nyquist sampling is a digital waveform called PCM (pulse code modulation).

The PCM output is transferred to a vocoder (voice coder), which compresses the digitized voice signal into either Rate Set 1 (RS1) with an output of 8 kbps, or Rate Set 2 (RS2) with an output of 13 kbps, depending on the type of vocoder. In CDMA, variable rate vocoders are used. The most common vocoder today is the RS1 EVRC (Enhanced Variable Rate Coder).

Variable Rate Vocoder

The variable rate vocoder employs a codec (coder/decoder) that compresses digitized speech from the analog-to-digital (A/D) converter and produces an output that complies with the data rate to be transmitted.

VCELP

One vocoder technique is called VCELP (vector code-excited linear predictive). VCELP produces high quality speech at lower bits rates, less than 16 kbps.

The essence of VCELP is the analysis-by-synthesis codebook search. The VCELP speech coder takes 160 samples of quantized speech and produces a variable number of bits in a 20 ms speech frame. The speech vector to be coded is matched against a codeword (codeword index, gain, pitch lag, and pitch gain) that minimizes the error between digitized and synthesized speech.

The vector (codebook index, gain and pitch parameters), and the LPF (linear predictive filter) coefficients are multiplexed and transmitted to the receiver. These parameters are used by the decoder in the receiver to reproduce the synthesized speech of the transmitter.

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Speech Activity

• Natural speech includes active periods and quiet periods– Spurts and pauses

• Variable bit rate coders tied to speech activity:– Full rate, 1/2 rate, 1/4 rate, 1/8 rate

– Lower coder rates means lower required transmit power.

pause

spurt

average talk cycle3.75 seconds

1.5seconds

2.25seconds

%4025.25.1

5.1 =+

=factoractivity Voice

Natural speech includes active periods and quiet periods called spurts and pauses. Spurts are generally syllables and words, while pauses include the times in a conversation when the party is listening. In a typical conversation, the speech spurts last between one and two seconds, and the activity factor is about 40% in a minimum talk cycle of 3.75 seconds. The average speech time and non-speech time can be modeled as shown in the figure.

By taking advantage of the variations in speech that occur during a normal conversation, the variable rate vocoder can dynamically change its rate. During normal speech, speakers take pauses and breaths, events in which no speech is transmitted. During these “lulls” in the conversation, the vocoder can reduce its bandwidth requirements, before the FEC encoder, from full rate (9600 bps for EVRC) to 1/2 rate, 1/4 rate, or 1/8 rate (1200 bps for EVRC).

Since the transmitter only transmits the lowest bit rate required, the required transmit power is minimized, and the channel interference is reduced.

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3.3 Frames And Quality Indicator

• Information bits are grouped into frames:– 20 ms (IS-95, IS-2000)

– 26.67 ms (IS-856)

• Number of bits per frame depends on data rate and additional information added to the frame

• A frame quality indicator can be added to each frame:– CRC

• Receiver uses indicator to determine frame in error• Various error rate measurements exists:

– BER

– FER

– PER

Frame

Information bits are grouped into frames. A frame is the basic timing interval in the system. The length of a frame depends on what channel on which it is transmitted (e.g., Sync Channel, Traffic Channel), what type of information transmitted in the frame (e.g., overhead messages, traffic information), and what air-interface standard is used (e.g., IS-2000, IS-856).

For a traffic channel transmitting traffic information, the frame length will be 20 ms for IS-95 and IS-2000, and 26.67 ms for IS-856. The number of bits per frame depends on the current data rate and if any additional information is added to the frame.

Frame Offset

A frame offset is a time skewing to Traffic Channel frames from System Time. The purpose of the frame offset is to spread out the exact transmission time for the channel so that the processing delay at the base station can be minimized, e.g., frames from different mobiles will arrive at the base station at different times.

Frame Quality Indicator

A frame may include a frame quality indicator, depending on what channel the frame is transmitted, and the data rate of the frame. The frame quality indicator can support two functions at the receiver. The first function is to determine whether the frame is in error. The second function may be to assist in the determination of the data rate of the received frame. Other parameters may be needed for rate determination in addition to the frame quality indicator, such as symbol error rate evaluated at different data rates.

The frame quality indicator is a Cyclic Redundancy Code (CRC). A CRC is a class of linear error detecting codes which generate parity check bits by finding the remainder of a polynomial division. The CRC is calculated on all bits within the frame, except the frame quality indicator itself and the encoder tail bits.

Error Measurements

There are a number of error measurements available in CDMA transmission: Bit Error Rate (BER), Frame Error Rate (FER), and Packet Error Rate (PER).

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3.4 Forward Error Correction

• Provides channel bit error detection and correction capability– Generates redundancy in the bit stream

– Simple example:• No encoding vs. multiply bits by 3

• Two types of FEC encoders:– Convolutional encoder (IS-95, IS-2000)

– Turbo encoder (IS-2000, IS-856)

• Viterbi decoder.

x3111 111 000 000 111

/31100111X XX1 0X0 0XX X1111001

11001 1XXX1

RFRF

Forward error correction (FEC) encoding provides channel bit error detection and correction capability at the receiver. FEC enables noise- and interference-free communication over a wide range of input signal-to-impairment conditions by adding redundancy to the bit-stream.

Encoding Process Example

Let’s say that the encoder receives a number of bits and multiplies them by three. If the input to the encoder is 11001, the encoder reproduces each bit by a factor of three. The resulting output is 111 111 000 000 111.

Multiplying the input data frame provides a measure of protection against loss of data caused by interference. Assume that a given frame is damaged during transmission, it is possible that the receiver would not be able to reconstruct the frame without having access to the additional bits. Using the example of 11001, if we did not encode the frame and it was damaged by interference, the received frame may be 1XXX1. The additional bits generated by the encoding process provide the receiver with a backup source that may allow it to reconstruct the original frame.

The FEC encoders used in CDMA are more sophisticated than the one shown in the example.

Encoders, Decoders

Two types of encoders are used in the technologies discussed in this course, convolutional encoder and turbo encoder. The decoder used is often the Viterbi decoder. The encoders and decoder will be discussed in more detail.

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r0 r1 r2 r3 r4 r5 r6 r7

+

+

Codesymbols(output)

Input

c0

c1

Convolutional Encoder

• Output depends on current and previous bits.– Constraint length, K, e.g., K=9

– Coding coefficient R, e.g., R=1/2• For every bit going into the encoder, two bits are coming out

– Encoder tail bits set to 0 at the end of frame clear the registers.

• Example: K=9, R=1/2.

95A 95B 3G 1xEV

The convolutional encoder and symbol repetition take advantage of the bandwidth in CDMA spread spectrum systems to introduce redundancy into the original data stream. The receiver uses the redundancy as an opportunity for error correction. Through the use of convolutionalencoding, symbol energy and transmit power can be reduced, and the system will still achieve the same FER (frame error rate).

Convolutional Encoder Characteristics

A convolutional encoder is primarily characterized by two parameters: The coding coefficient, R, and the constraint length, K.

The coding coefficient, R, determines the amount of redundancy to be generated in the bit stream. For example, R=1/2 means that for every bit going into the encoder, two bits are produced by the encoder.

The constraint length, K, determines the “memory” of the convolutional encoder, or the number of shift-registers (K-1). The output from the encoder depends not only on the bit currently going into the encoder but also on the previous bit that has passed through the encoder. A long memory creates a more robust bit stream but it also creates more delay in the transmission. Also, the benefit of the convolutional encoder versus the complexity is diminishing as K becomes greater than nine.

Modulo-2 Addition (XOR)

The table shows the modulo-2 addition operation.Modulo-2 addition can be realized using XOR gates.

011

101

110

000

A XOR BBA

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Convolutional Encoder - Example

95A 95B 3G 1xEV

r0 r1 r2 r3 r4 r5 r6 r7

+

+

Codesymbols(output)

Input

c0

c1

11 10 10 1111000001101…

10 10 1110000000110…1

10 1110000000011…1 0

1111000000001…1 0 1

00000000…1 0 1 1

Bits sent (c1 c0)c1c0r7r6r5r4r3r2r1r0InputBits left

The slide illustrates a convolutional encoder (K=9, R=1/2 ) in the process of transmitting the information bit stream, 1 0 1 1.

The previous frame transmitted has filled the encoder’s shift registers (r0, r1, r2, …) with zeroes using the encoder tail bits to clear the encoder. When each bit is fed into the encoder, the output depends on the input an each of the shift register’s values. Since the encoder has a coding coefficient of R=1/2, two output bits (symbols) are generated for each input bit.

When the input bit stream is 1 0 1 1, the output will be 1 1 1 0 1 0 1 1.

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Turbo Encoder

95A 95B 3G 1xEV• “Two convolutional encoders operating inparallel”– Input: turbo interleaver

– Output: concatenated, repeated and punctured

• More robust than convolutional codes– Can increase throughput– Adds additional delay to the traffic data.

TurboInterleaver

Encoder#1

Encoder#2

Puncture &Repeat

Input

Output

The turbo encoder can be seen as two convolutional encoders operating in parallel. The convolutional encoders are also called constituent encoders. A turbo interleaver selects the input to each convolutional encoder. The output of the two convolutional encoders are concatenated with the appropriate symbol repetition and puncturing to achieve the correct symbol rate.

Turbo codes are more robust than convolutional codes but add additional delay to the traffic data. Therefore, turbo codes are not suitable for voice traffic, but function well for data traffic.

Andrew Viterbi explains: “Turbo codes are mixture of simple short convolutional codes, longinterleavers and better soft decision decoding, which permit data rates to approach within 60% to 80% of the Shannon coding limit (an amazing feat), thus increasing current throughputs by more than 60%.” Putting it in simple words, turbo codes do a lot of processing to encode relatively large chunks (frames) of information before transmission and to extract it upon reception. The overall process is resistant to interference approaching 80% of the theoretical capacity limit.

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Viterbi Decoder

• Developed and analyzed in 1967 by A.J. Viterbi• Efficient in determining the most likely bit sequence

based on symbol organization• Decoding algorithm is proprietary to Qualcomm.

Reference: Viterbi, A.J., “Error Bounds for Convolutional Codes and Asyptotically OptimumDecoding Algorithm,” IEEE Trans. Inf. Theory, col IT13, April 1967, pp. 260-269

Decoding an encoded signal is much more complex than encoding the signal. The Viterbi decorder is often used as the decoder.

Viterbi Decoder

The Viterbi decoder is the final step the frame encounters as part of a CDMA-specific transmission. The Viterbi decoder receives the frame from the deinterleaver and, based upon the organization of the symbols in the frame, determines the most likely sequence of bits in the frame (maximum likelihood decoding). Given the encoder bit redundancy (coding coefficient) and memory (constraint length), the decoder can detect and correct corrupt encoder symbols.

The algorithm used to perform Viterbi decoding is proprietary to Qualcomm, and is incorporated in chip sets purchased or licensed from Qualcomm.

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Symbol Repetition & Puncturing

• Encoder symbols (output) are repeated and punctured as necessary before interleaving.– Ensure constant symbol rate for interleaver

– Depends on channel and data rate.

The output from the encoder is called encoder symbols. These symbols are repeated and punctured as necessary before entering the bit interleaver. The purpose is to ensure a constant symbol rate for the interleaver. Also, when a symbol is repeated N times, its transmit power can be reduced by a factor of N and still provide the same energy for the receiver.

Repeating the symbols will generate even more redundancy, whereas puncturing of symbols will reduce the redundancy. How often to repeat and puncture the symbols depends on the channel used and the data rate transmitted.

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3.5 Bit Interleaving

• Rearranges bits to eliminate bit error bursts– Writes the bits into a matrix in a specific pattern

– Transmits the bits from the matrix in a different pattern

• Enables the channel decoder process to work under fading conditions– Receiver deinterleaves the bits back into correct order

• Example:– Transmitter

• Enter bits column-wise• Transmit bits row-wise

– Receiver• Enter bits row-wise• Recover bits column-wise. Interleaver matrix

The bit interleaver works closely with the encoder to provide additional communication reliability by interleaving the encoded bits so that the transmitted frame is, essentially, transmitted multiple times. The decoder is very efficient in detecting and correcting non-consecutive corrupted bits, but not as efficient for consecutive corrupted bits. With interleaving, the decoder is provided with additional opportunities to reconstruct frames damaged during transmission. When the frame is deinterleaved, the bits are restored to their encoded position. The decoder in the receiver is able to compare the received bits with those immediately adjacent, and decode the speech frame into a duplicate of the original.

The block interleaver randomizes the bits to further reduce the effects of interference. Through the process of encoding, code repetition and block interleaving, the potential for one or more frames to be completely undecipherable by the receiver is substantially reduced. These processes are crucial to maintaining a low FER.

The coded signal is interleaved by writing a block of coded bits into an array, a matrix, according to a bit pattern and then reading from that array according to another bit pattern.

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Bit Interleaving - Example

• Interleave and deinterleave the bit stream– b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 b16

• Step 2: Transmit bits row-wise– b1 b5 b9 b13 b2 b6 b10 b14 b3 b7 b11 b15 b4 b8 b12 b16

• Step 1: Enter bits column-wise

• Bit-errors– b1 b5 b9 b13 b2 b6 b10 b14 b3 b7 b11 b15 b4 b8 b12 b16

• Step 4: Recover bits column-wise– b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 b16

• Step 3: Enter bits row-wise

¤

Interleaver matrix

b16b12b8b4

b15b11b7b3

b14b10b6b2

b13b9b5b1

b16b12b8b4

b15b11b7b3

b14b10b6b2

b13b9b5b1

Deinterleaver matrix

X XX X

X X X X

X X X X

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Summary

• Transmitted speech needs to be encoded by a vocoder.• Forward error correction (FEC) encoding is used to make

signal more robust.– Convolutional encoder

– Turbo encoder

• FEC Decoder can detect and correct corrupt bits.• Bit interleaving spreads out corrupt bits.

– Works with FEC decoder.

Before a digital information signal is transmitted, it is encoded to make it more suitable for transmission.

If speech is transmitted, it has to be encoded using a vocoder. The vocoder transforms the speech information into information symbols that can be more efficiently transmitted. An additional benefit of the vocoder is that the data rate of the vocoder can vary based on the activity (amount of information during a time period) of speech. A CDMA vocoder supports varying speech activity by using full rate, 1/2 rate, 1/4 rate, and 1/8 rate operation.

Every information signal undergoes forward error correction (FEC). FEC is a process with which the information signal is transformed into a bitstream with more bits than the original information signal. When the encoded bitstream arrives at the decoder, the decoder can detect and correct corrupt bits in the original information signal. Two FEC techniqies are used in CDMA: convolutional coding (used in IS-95 and IS-2000), and turbo coding (used in IS-2000 and IS-856).

FEC works best on occasional corrupt bits; however, in an RF environment, RF fades generates consecutive corrupt bits that the FEC decoder may not be able to correct. To maximize the efficiency of the FEC decoder, the bits are interleaved before transmission. When interleaved, the bits are not transmitted in their natural order. If an RF fade generates consecutive corrupt bits, the deinterleaver will spread out those bits and make it easier for the FEC decoder to correct them.

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Knowledge Check

1. Given the bit stream: 1 0 1 1Encode, interleave, deinterleave, and decode the bit stream– Use encoder that multiplies bits by 4

– Use a 4x4 interleaver/deinterleaver matrix

– When transmitted, the middle four bits are corrupt

What’s the received and decoded bit stream?– See next page for a worksheet.

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1. Worksheet

Step 1: Encode (x4) the bitstream 1 0 1 1

Step 2: Interleave (4x4). Enter bits column-wise, transmit row-wise

Step 3: Transmit. Middle four bit are received corrupt

Step 4: Deinterleave. Enter bits row-wise, recover column-wise

Step 5: Decode.

Interlea

ver matrix

Deinterleave

rm

atrix

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2. When FER is greater than 0%, then BER must be greater than 0%.A. True

B. False

3. When BER is greater than 0%, then FER must be greater than 0%.A. True

B. False

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4. Why are the information bits grouped into frames?A. To increase the data rate of the transmission

B. To accommodate FEC and bit interleaving

C. To reduce facility cost by packetizing the information

D. Any of the above

5. A turbo encoder with an R = 1/4 factor indicates that for every one information bit to be transmitted, three bits are added to greatly improve the accuracy of the information being received.A. True

B. False

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Lesson 4CDMA Codes

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Lesson Objectives

• Explain code-correlation• Describe the codes used in CDMA• Explain orthogonality• Explain digital modulation.

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4.1 Typical Signal Processing

DigitalModulation

SpeechEncoding

RFModulation

QualityIndicator

FECEncoding

Interleaving


Information

Lesson 3

Lesson 4

Amp

But first, codes and correlationBut first, codes and correlation

CDMA Transmitter

Before the digital information signal can be transmitted in the RF environment, it must undergo a number of signal processing steps. The general steps a transmitted signal undergoes is shown in the graphic. The steps are, but not limited to:

•Speech encoding: This step is only used if speech information is transmitted. Data transmission omits this step.



•Interleaving

•Scrambling

•Spreading


•RF modulation



CDMA Receiver

At a CDMA receiver, similar steps take place but in the reverse order, i.e., first the received signal is demodulated, then de-spread, de-scrambled, de-interleaved, etc.

In this lesson, we will take look at the use of codes in CDMA, and what code correlation means.

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4.2 Code Correlation

Autocorrelationof 15 bit sequence

15Tc

-1/15

s15 bit

equence

10

-1-

1

- 0 - 0 11 05 5 1 50- 51

• Multiply regenerated PN code sequence with incoming sequence.

• Average the result and look for maximum.

• If not maximum, shift regenerated sequence and repeat.

• To maintain close chip- and code-synchronization, GPS time is used as reference.

bitshift

The average of the product of the 15 bit PN code with a shifted version of itself is shown for various bit shifts. The plot of the average value calculated over the code period for all bit shifts is called the autocorrelation function. It can be seen that when the signals are synchronized (bit shift = 0), the autocorrelation is very high.

In order for CDMA to maximize performance, the codes must be aligned. GPS time is used as the time reference in a CDMA network to aid the transmitter and receiver when they are synchronizing their codes.

Examle

‘+1’ is represented as ‘+’ and ‘-1’ as ‘-’.

Bit shift = 0

PN15(t) x PN15(t) =

= (+ + + + - - - + - - + + - + -) x (+ + + + - - - + - - + + - + -) / 15 =

= (+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1) / 15 =

= 1

Bit shift = -4

PN15(t) x PN15(t - 4) =

= (+ + + + - - - + - - + + - + -) x (+ - + - + + + + - - - + - - +) / 15 =

= (+1-1+1-1-1-1-1+1+1+1-1+1+1-1-1) / 15 =

= -1 / 15

Note: If the signal is the same or a shifted version of itself, then the correlation is called an autocorrelation. If the signal is different from either signal, then the correlation is call a cross-correlation.

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Pseudo Noise Code-Sequence Generator

1 2 3 4

+ Output

Clock 1 2 3 4 Output0 1 0 0 0 01 0 1 0 0 02 0 0 1 0 03 1 0 0 1 14 1 1 0 0 05 0 1 1 0 06 1 0 1 1 17 0 1 0 1 18 1 0 1 0 09 1 1 0 1 110 1 1 1 0 011 1 1 1 1 112 0 1 1 1 113 0 0 1 1 114 0 0 0 1 115 1 0 0 0 0

RegisterClock 1 2 3 4 Output

0 1 0 0 0 01 0 1 0 0 02 0 0 1 0 03 1 0 0 1 14 1 1 0 0 05 0 1 1 0 06 1 0 1 1 17 0 1 0 1 18 1 0 1 0 09 1 1 0 1 110 1 1 1 0 011 1 1 1 1 112 0 1 1 1 113 0 0 1 1 114 0 0 0 1 115 1 0 0 0 0

Register

• PN generator using shift registers with XOR feedback

• Periodicity, L = 2m – 1where m is the number of shift registers.

Introduction

A direct sequence (DS) or pseudo-noise (PN) stream is generated in an m-stage maximal-length shift register. The sequence, or PN code, that is produced at the output repeats itself after a maximum period of time corresponding to 2m -1 shifts. The smallest time increment in the output sequence is of duration Tc, which is called the time chip. For the resulting output waveform to have the desired pseudo-noise property, the outputs of certain stages must have feedbackconnections that are made in a certain fashion.

Example

In the illustration shown, we are feeding back the modulo-2 sum (XOR) of stage m and m-1 to the input to obtain the output. Different feedback connections result in distinct coded outputs.

Codes generated by a maximal-length PN code generator have the time period given by

TPN = LTc

where L is the number of chips that make up the period:

L = 2m - 1

The waveform shown comes from a four stage register, m=4, with modulo-2 connections of Stages 3 and 4 fed back to Stage 1 as shown.

The initial states of the stages in the register is 1 0 0 0. The output sequences through all 24 - 1 = 15 states are summarized in the state table.

Modulo-2 Addition (XOR)

The table shows the modulo-2 addition operation.Modulo-2 addition can be realized using XOR gates.

011

101

110

000

A XOR BBA

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4.3 CDMA Codes

• The codes used in CDMA are:– Long code (242 – 1 bits)

– Short code (215 bits)

– Walsh code (4 – 256 bits)

• Pseudo-random noise (PN) characteristics• The codes have different functions:

– Scrambling

– Spreading

– Digital modulation

– Identification

• The function depends on:– Forward or reverse link channel

– Technology used.

PN Long Code

The long code gets its name from the fact that it takes about 41.4 days for the code to repeat itself. Information about the long code is broadcast to the mobile station by the Sync Channel (or Control Channel) to help the mobile lock onto the base station, and helps provide separation from other base stations.

PN Short Code

One of the codes used in conjunction with the Walsh Code is the PN (pseudo-random noise) short code. The PN short code on the forward link is used to provide the base station with a unique identification that the mobile station uses to identify the serving base station.

Because CDMA communication is conducted on a common frequency with several calls in progress simultaneously, identifying the serving base station and sector is an important issue for the mobile station. In addition, DS CDMA operates at the RF (radio frequency) noise floor, adding to the difficulty in detecting and decoding the transmitted signal. As a result, the mobile must have a way to detect and communicate with the serving base station/sector from among all the surrounding base stations and sectors.

Walsh Function

The user signal (or control channel) is multiplied by the Walsh code. The Walsh code provides each user or channel with a unique identifier and, in DS spreading, may spread the frame across the bandwidth.

CL8300-SG.en.UL 89



4.4 Long Code

• Long code is 242-1 bits long– Periodicity of 41.4 days

• Typically used for scrambling and identification– Forward link: Scrambles information

– Reverse link: Identifies mobile

• Long code is masked with a long code mask.

r0 + r1 r2 r3 r4 r5 r41r40+ + +

Modulo-2 addition

42-bit longcode mask

Effectivelong code

The long code is generated using a PN code-sequence generator with 42 stages, or shift-registers. The length of the long code is 242-1 bits long. With a rate of 1.2288 Mbps, the code repeat itself approximately every 41.4 days. The characteristic polynomial used to generate the long code is defined in the standard specifications as:

p(x) = x42 + x35 + x33 + x31 + x27 + x26 + x25 + x22 + x21 + x19 + x18 + x17 + x16 + x10 + x7 + x6 + x5 + x3 + x2 + x1 + 1

In addition to the code-sequence generator, a long code mask is used to generate an effective long code that is unique to the channel or user in question. The effective long code is typically used to scramble the bit-stream transmitted, or to assign a unique identification to a user.

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Long Code Masks

1100011000 Public Permuted ESN

41 32 31

Traffic Channel

0

Access Channel

41 033 32 28 27 25 24 9 8

110001111 Paging ChNumber

Base Station Id Pilot Offset IndexAccess ChNumber

or

41

Private (specified in controlled appendix)

0

Note: The masks used in IS-856 are defined somewhat differently

Note: The masks used in IS-856 are defined somewhat differently

Traffic Channel

When the long code mask is used for traffic channel, public or private versions are possible.

The public mask uses the mobile station’s electronic serial number (ESN) in a permutation specified in the standard. The permutation prevents high correlation between long codes corresponding to consecutive ESNs. Note that this is not encryption, since the ESN is known, then the mask is known.

The private long code mask is determined by referring to a controlled appendix of the standard. The distribution of the appendix is controlled by TIA.

Access Channel

The access channel number is the channel number being used by the mobile to initiate communication with, or respond to a message from, the base station with a specific identification number.

Note: The masks shown are to illustrate the concept. The masks used for IS-856 channels are defined in a slightly different way.

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4.5 Short Codes

• Short codes are 215 bits (32768 bits) long– In-phase code, PNI

– Quadrature-phase code, PNQ

• Same codes used everywhere– Shifted versions used

• PN-I-i(t) = PNI(t - i* 64*Tc)• PN-Q-i(t) = PNQ(t - i* 64*Tc)

– Each shift is 64 bits, called an offset

– Total 512 offsets (32768 / 64)

• Typically used for spreading and identification– Forward link: Quadrature spreading with specific offset identifying

antenna face– Reverse link: Quadrature spreading with zero-offset.

The short codes, or PN short codes, are 215 bits long and are used for both spreading and identification. In-phase and quadrature-phase components have different short codes, PNI and PNQ, respectively. The characteristic polynomials used to generate the short codes are defined in the standard specifications as:

PNI(x) = x15 + x13 + x9 + x8 + x7 + x5 + 1

PNQ(x) = x15 + x12 + x11 + x10 + x6 + x5 + x4 + x3 + 1

Note: For IS-856, the short codes used on the forward link are specified as:

PNI(x) = x15 + x10 + x8 + x7 + x6 + x2 + 1

PNQ(x) = x15 + x12 + x11 + x10 + x9 + x5 + x4 + x3 + 1

PNI [PN-I-i(t)] and PNQ [PN-Q-i(t)] for different cells and sectors are distinguished by time offset index from the basic code: the zero offset sequence, PN-I-0(t) and PN-Q-0(t) (i.e., i = 0). Signals transmitted from a single antenna in a particular CDMA radio channel share a common PN code phase (or time offset). Including the zero offset sequences, PN-I-0(t) and PN-Q-0(t), there are 512 possible time offset indices to identify cells. Each time offset is 64 chips, and PN-I and PN-Q are identified by an offset index, 0 through 511, from the zero offset PN sequence, PN-I-0, PN-Q-0. This can be expressed as:

PN-I-i-(t) = PN-I-0 (t-i x 64Tc)

PN-Q-i(t) = PN-Q-0 (t-i x 64Tc)

where i = 0, 1, 2,...511, and Tc is the chip duration.

The time offsets used for the PN code is based on orthogonal coding in which the spread signal is split and sent to a quadrature spreader whose output is offset by 90 degrees. On the reverse link, the quadrature spreader is using the zero-offset PN codes.

CL8300-SG.en.UL 92



PN Offset For Sector Identification

PN(t-0)

-1

-1

1

0

1

0

PN(t-4Tc)

Note: PN(t-0) x PN(t-4Tc) = -1/15Note: PN(t-0) x PN(t-4Tc) = -1/15

The forward link uses a pilot signal to allow the mobiles in the cell to synchronize to the base station. The pilot is to be used by the mobile demodulator to provide a coherent reference which is effective even in a fading environment, because the desired signal and the pilot fade together. All users in the same cell (or sector) share the same quadrature pair of modified PN codes, often referred to as pilot PN offset.

Each base station will use the same PN short codes with a different offset, PN offset. Since these codes have different offsets, they will have very low correlation with each other. Mobiles identify their serving base station by looking for the appropriate offset assigned to the given base station. Shown in the figure are two PN sequences which differ only in their offset.

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4.6 Walsh Codes

• Walsh codes range between 4 and 256 bits– Depends on technology

– Also known as Walsh functions

• Typically used for identification– Identifying channels

– IS-95 reverse link uses Walsh codes for digital modulation

• Walsh codes used must be orthogonal– Orthogonal: “Having a sum of products or an integral that is zero”

• Cross-correlation = 0

– Must be time-aligned to have zero correlation.• Not always zero cross-correlation at other alignments

– Hadamard matrix generates orthogonal codes.

The Walsh codes, or Walsh functions*, are a set of codes that range from 4 to 256 bits. One of the main functions of the Walsh codes is to identify channels that are being transmitted. In order to efficiently identify the channels, Walsh codes must be orthogonal (correlation between two different codes equal 0) and orthonormal (correlation between the same code equal 1).

To generate orthogonal Walsh codes, CDMA uses the Hadamard matrix.

Note: Walsh codes must be time-aligned to have zero correlation. They do not always have a zero cross-correlation at other alignments.

* See:Beauchamp, K. G., Applications of Walsh and Related Functions, Academic Press, N.Y., 1984J. Hadamard, Résolution d'une question relative aux déterminants, Bull. Sci. Math. 17, 1893

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Hadamard Matrix

• Used to generate orthogonal codes– Use copies of previous matrix and its inverse

– Walsh codes written as WkN

• N = Length of Walsh code• k = Walsh code index of length N

• Example:

Hn HnHn Hn

H2n =

0H0 = 0 00 1

H2 =0 0 0 00 1 0 10 0 1 10 1 1 0

H4 =

0 0 0 0 0 0 0 00 1 0 1 0 1 0 10 0 1 1 0 0 1 10 1 1 0 0 1 1 00 0 0 0 1 1 1 10 1 0 1 1 0 1 00 0 1 1 1 1 0 00 1 1 0 1 0 0 1

H8 =

¤

W78 = 0 1 1 0 1 0 0 1

The Hadamard matrix generates codes that are orthogonal. The process to generate the codes can be seen in the slide.

A Hadamard matrix of size NxN is said to have N Walsh codes of length N. In other words, there are as many orthogonal Walsh codes as there are bits in a Walsh code. For example, Walsh code W7

8 consists of 8 bits.

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Walsh Code Orthogonality – Example #1, Same Length

t

1

0

-1

tT

T4

T2

1

0

-1

1

0

-1

W28

T8

x t

Average =

+1-1+1-1+1-1+1 1

= 0T

W78

W78

W28

Code length = TCode length = T

W78 = 0 1 1 0 1 0 0 1W78 = 0 1 1 0 1 0 0 1

W28 = 0 0 1 1 0 0 1 1W28 = 0 0 1 1 0 0 1 1

Shown is an example where the correlation (cross-correlation) is calculated for two different Walsh codes, W2

8 and W78. When integrating over the code length (8 chips), the value is zero, or

close to zero. Please note that when calculating the correlation for the same code, e.g., W28 and

W28, the value will be 1 (or close to some constant).

Note: Multiplying voltages (+1, -1) is the same as performing modulo-2 addition on the bit-values (0, 1).

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Walsh Code Orthogonality – Example #2, Different Length, Orthogonal

t

1

0

-1

tT

T4

1

0

-1

1

0

-1

W24

x t

W78

W78

W24


3T4

Averagecode 1 =

+1-1+1-1 = 0T

Averagecode 2 =

-1+1-1+1 = 0Tcode 1code 1 code 2code 2

2T

W78 = 0 1 1 0 1 0 0 1W78 = 0 1 1 0 1 0 0 1

W24 = 0 0 1 1W24 = 0 0 1 1

Shown is an example where the correlation (cross-correlation) is calculated for two different Walsh codes, W2

4 and W78. The code length used for integration is now four chips instead of

eight (as in previous example). Even though the code length differs between the two codes, when integrating over the code length, the value is still zero or close to zero, indicating that the two codes are orthogonal.


CL8300-SG.en.UL 97



Walsh Code Orthogonality – Example #3, Different Length, Non-Orthogonal

t

1

0

-1

tT

1

0

-1

1

0

-1

W24

x t

W68

W68

W24


Averagecode 1 =

+1+1+1+1 = +1T

Averagecode 2 =

-1-1-1-1 = -1Tcode 1code 1 code 2code 2

T3T4 2T

4

W78 = 0 0 1 1 1 1 0 0W78 = 0 0 1 1 1 1 0 0

W24 = 0 0 1 1W24 = 0 0 1 1

In this example two different Walsh codes, W24 and W6

8 are compared. The code length used for integration is four chips. When integrating over the code length, the value is not zero, indicating that the two codes are not orthogonal.


CL8300-SG.en.UL 98



Why Are W24 and W6

8 Not Orthogonal?

• W24 from H4 is repeated in H8, both in original and

inverted form.– Therefore, the codes are not orthogonal.

• With the same logic, W24 would not be orthogonal with

W216, W6

16, W1016, and W14

16.• It would be nice to have a table that showed what Walsh

codes are orthogonal with what Walsh codes…

0 0 0 00 1 0 10 0 1 10 1 1 0

H4 =

0 0 0 0 0 0 0 00 1 0 1 0 1 0 10 0 1 1 0 0 1 10 1 1 0 0 1 1 00 0 0 0 1 1 1 10 1 0 1 1 0 1 00 0 1 1 1 1 0 00 1 1 0 1 0 0 1

H8 =

If Walsh codes of variable length are used together, then a shorter code precludes using all longer codes derived from the shorter code.

CL8300-SG.en.UL 99



Walsh Code Orthogonality Table

W4 W8 W16 W32 W64 W1280 0

0 6432 32

0 9616 16

16 8048 48

0 1128 8

8 7240 40

8 10424 24

24 8856 56

0 1204 4

4 6836 36

4 10020 20

20 8452 52

4 11612 12

12 7644 44

12 10828 28

28 9260 60

124

Walsh Code LengthsW4 W8 W16 W32 W64 W128

0 00 64

32 320 96

16 1616 80

48 480 112

8 88 72

40 408 104

24 2424 88

56 560 120

4 44 68

36 364 100

20 2020 84

52 524 116

12 1212 76

44 4412 108

28 2828 92

60 60124

Walsh Code Lengths• The table shows orthogonality relationships between Walsh codes.– Parts 1 and 3

shown in slide

• Rule:– Walsh codes on

the same row are not orthogonal

W4 W8 W16 W32 W64 W1282 2

2 6634 34

2 9818 18

18 8250 50

2 11410 10

10 7442 42

10 10626 26

26 9058 58

2 1226 6

6 7038 38

6 10222 22

22 8654 54

6 11814 14

14 7846 46

14 11030 30

30 9462 62

126


2 22 66

34 342 98

18 1818 82

50 502 114

10 1010 74

42 4210 106

26 2626 90

58 582 122

6 66 70

38 386 102

22 2222 86

54 546 118

14 1414 78

46 4614 110

30 3030 94

62 62126

Walsh Code Lengths

If Walsh codes of variable length are used together, then a shorter code precludes using all longer codes derived from the shorter code. The tables show the orthogonality relationships between Walsh codes of variable length.

Rule

Walsh codes appearing on the same row are not orthogonal with each other. Walsh codes that do not share one or more rows with another Walsh code in use are orthogonal.

Example

Walsh code W5264 is not

orthogonal with W04, W4

8, W4

16, W2032, W52

128, and W116128.

However, it is orthogonal with, for example, W12

64 and W84128.

W4 W8 W16 W32 W64 W1283 3

3 6735 35

3 9919 19

19 8351 51

3 11511 11

11 7543 43

11 10727 27

27 9159 59

3 1237 7

7 7139 39

7 10323 23

23 8755 55

7 11915 15

15 7947 47

15 11131 31

31 9563 63

127


3 33 67

35 353 99

19 1919 83

51 513 115

11 1111 75

43 4311 107

27 2727 91

59 593 123

7 77 71

39 397 103

23 2323 87

55 557 119

15 1515 79

47 4715 111

31 3131 95

63 63127

Walsh Code Lengths

Parts 2 and 4 of the Walsh code orthogonality table

W4 W8 W16 W32 W64 W1281 1

1 6533 33

1 9717 17

17 8149 49

1 1139 9

9 7341 41

9 10525 25

25 8957 57

1 1215 5

5 6937 37

5 10121 21

21 8553 53

5 11713 13

13 7745 45

13 10929 29

29 9361 61

125


1 11 65

33 331 97

17 1717 81

49 491 113

9 99 73

41 419 105

25 2525 89

57 571 121

5 55 69

37 375 101

21 2121 85

53 535 117

13 1313 77

45 4513 109

29 2929 93

61 61125

Walsh Code Lengths

CL8300-SG.en.UL 100



Quasi-Orthogonal Codes

• To gain more Walsh codes, quasi-orthogonalcodes may be used.– Not fully orthogonal

• Generated by adjusting existing Walsh code– Change sign of bit-value:

• Bit 0 => *1• Bit 1 => *(-1)

– Rotate phase when transmitting:• Bit 0 => 0º• Bit 1 => 90º

• See IS-2000 for more detail.

95A 95B 3G 1xEV

IS-2000 provides the functionality to expand the Walsh code space by using so called quasi-orthogonal Walsh codes (or Walsh functions). While this may seem like a desirable feat, it is important to keep in mind that the quasi-orthogonal codes are not fully orthogonal. This means that two different codes are interfering with each other to some degree.

Quasi-orthogonal functions (QOFs) are created using a non-zero sign multiplier QOF mask and a non-zero rotate enabling Walsh code as specified in IS-2000. The repeated sequence of an appropriate Walsh code is multiplied by the repeated sequence of masks with symbols +1 and -1, which correspond to the sign multiplier QOF mask values of 0 and 1, respectively. The sequence is also multiplied by the repeated sequence of masks with symbols 1 and j (j is the complex number representing a 90o phase shift), which correspond to the rotate enable Walsh function values of 0 and 1, respectively.

CL8300-SG.en.UL 101



CDMA Codes Summary

• The codes used in CDMA are:– Long code (242 - 1 bits)

– Short code (215 bits)

– Walsh code (4 – 256 bits)

• They work together.– Forward link:

• Short code (PN offset) identifies antenna face• Walsh code identifies channels within the antenna face

– Reverse link:• Long code identifies users• Walsh code may be used to identify channels

• The codes also perform scrambling and spreading.

CL8300-SG.en.UL 102



4.7 Scrambling & Spreading

• Main process:– y(t) = b(t) c(t)

• Scrambling:– If b(t) and c(t) have the same rate then y(t) has the same rate,

and the spectrum of the signal is unchanged– b(t) is said to be encrypted or scrambled

• Spreading:– If c(t) has a higher rate than b(t), y(t) has the faster rate and its

correspondingly wider spectrum– In addition to being scrambled, b(t) is said to have had its

spectrum spread

• CDMA codes are used to perform scrambling and spreading.– See the technology specific lessons for more details.

Assuming that the main process performed is the multiplication of two signals, b(t) and c(t) so that y(t)=b(t)c(t), scrambling and spreading can be explained.

Scrambling

When b(t) and c(t) have the same rate, the product y(t)=b(t)c(t) contains all the information of b(t) and has the same rate. The spectrum of the signal is unchanged, and the incoming bit stream is said to be encrypted or scrambled.

Spreading

When two signals, b(t) and c(t), are multiplied together, the resulting signal, b(t)c(t), will have the same bit (or chip) period as the faster signal (wider bandwidth); in this case, c(t). The signal b(t) can be seen as altering the phase of the spreading signal c(t).

Observe that the combined signal waveform shown has more high frequency changes than the changes in the data information since (1/Tc) >> (1/Tb). Note that Tb is the bit interval of the information stream, and Tc is the bit interval of the DS stream. Tc is also called a chip time.

When c(t) is faster, y(t) contains all the information of b(t), and it has the faster bit rate and its correspondingly wider spectrum. In addition to being scrambled, b(t) is said to have had its spectrum spread.

CL8300-SG.en.UL 103



4.8 Digital Modulation

• Modulation in the digital domain:– Bit patterns generate certain energy in the quadrature-phase (Q-

phase) and in-phase (I-phase) bit stream

– Creates a vector (i, q) with a certain amplitude and phase [a, ϕ]– Example, BPSK:

• 0: (i, q) = (+x, +y)• 1: (i, q) = (-x, -y)

– Example, QPSK:• 00: (i, q) = (+x, +y)• 01: (i, q) = (-x, +y)• 11: (i, q) = (-x, -y)• 10: (i, q) = (+x, -y)

• Multiply with PN short codes– Quadrature spreading.

I-phase

Q-phase

Constellation diagram

Digital Modulation

With digital modulation the bit or bit pattern generates certain energies in the quadrature-phase (Q-phase) and in-phase (I-phase) components of a signal. Several different digital modulation techniques exist:

•Binary Phase Shift Keying (BPSK): Transmits 1 bit at a time, used in IS-95

•Quadrature Phase Shift Keying (QPSK): Transmits 2 bits at a time, used in IS-2000 and IS-856

•8-ary Phase Shift Keying (8-PSK): Transmits 3 bits at a time, used in IS-856

•16-ary Quadrature Amplitude Modulation: Transmits 4 bits at a time, used in IS-856.

The I and Q components are then multiplied with a PN sequence (short code); this is calledquadrature spreading*. Quadrature spreading ensures that other-user interference appears as though it has both random phase and amplitude information (i.e., looks like bandlimitedGaussian noise).**

* For analytical details, refer to: Ziemer, R. E. and Peterson, R. L., Digital Communications and Spread Spectrum Systems, MacMillan, N.Y., 1985, pp. 340-343.** Viterbvi, A. J., "Very low rate convolutional codes for maximum theoretical performance of spread-spectrum multiple-access channels," IEEE Journal on Selected Areas in Communications, Vol. 8, No. 4, pp. 641-649, May 1990.

CL8300-SG.en.UL 104



RF Modulation and Amplification

• Modulation in the RF domain– Performed with quadrature mixer:

• q * sin(2πfct)• i * cos(2πfct)

• RF amplification:– Amplifies the RF signal after modulation

– Digital channel have their individual gain.

Quadrature Mixer

Σx

x

BasebandFilter

BasebandFilter

QuadratureSpreading/Scrambling

PNI PNQsin(2πfct)

cos(2πfct)

I

Q

I’

Q’Channels

RF

RF Modulation

The orthogonality of cosines and sines makes it possible to transmit and receive two independent signals simultaneously on the same carrier frequency. This is known as quadrature modulation. In the quadrature mixer, the Q-phase and I-phase are multiplied with sin(2πfct) and cos(2πfct), respectively, making the signal a RF signal.

Quadrature modulation is an efficient method of transmitting two message signals within the same bandwidth. It requires precise phase synchronization of transmitter and receiver.

RF Amplification

Once the signal has been modulated in the RF domain, it passes through an RF amplification process to generate the signal strength needed for RF transmission.

CL8300-SG.en.UL 105



Typical Signal Processing Summary

DigitalModulation

SpeechEncoding

RFModulation

QualityIndicator

FECEncoding

Interleaving


Information

Lesson 3

Lesson 4

Amp

CDMA Transmitter

Before the digital information signal can be transmitted in the RF environment, it must undergo a number of signal processing steps. The general steps a transmitted signal undergoes is shown in the graphic. The steps are, but not limited to:

•Speech encoding. This step is only used if speech information is transmitted. Data transmission omits this step.



•Interleaving

•Scrambling

•Spreading


•RF modulation



CL8300-SG.en.UL 106



4.9 Receiver

• Receiver must perform most signal processing steps in the reverse order.

• Multi-user environment:– Combining the CDMA codes makes each user and channel

unique in the area

– Receiver knows what codes to look for• All other codes appear as noise.

Digital De-Modulation

Speech De-coding

RF De-Modulation

FEC De-coding

De-Interleaving

De-Scrambling

De-Spreading

Information

Receiver Processes

Just as the transmitter is “wrapping” the information signal in a number of signal processing layers, the receiver must “unwrap” the signal by performing the signal processing steps in the reverse order:

•De-modulation

•De-spreading

•De-scrambling

•De-interleaving

•De-coding (FEC)

•De-coding (speech), if speech information is transmitted.

Multi-User Environment

An information signal in a multi-user environment can be detected if the correct CDMA codes are known. The combination of a set of codes (long code, short code, Walsh code) makes that information signal appear unique; all other code combinations appear as noise.

CL8300-SG.en.UL 107



End-To-End Overview

y(t)

1.2288 Mbps RF pathwith delay τ

Receive

c(t - τ)

b(t - τ)

codeddigital

informationdespreader

RegeneratedPN code

(1.2288 Mbps)

Mod

RFModulator

RF carrier

y(t - τ)

1.2288 Mbps

Transmit

c(t)

b(t)

codeddigital

informationspreader

PN code1.2288 Mbps

Demod

RFDemodulator

RegeneratedRF carrier

Transmitter

Low bit rate speech, b(t), is spread by multiplying it with a high bit rate PN (pseudorandom noise) code, c(t). The spread signal, b(t)c(t), is modulated by multiplication with an RF carrier and transmitted.

Receiver

The spread signal arriving at the receiver for a traffic channel, i, is zi(t) + noise, where zi(t) contains the desired signal and other channels. After RF de-modulation, a locally generated DS sequence that is an exact replica to the desired DS code transmitted multiplies the received signal - despreading. The received signal is delayed τ seconds, and the generated DS sequence must be in perfect synchronization (receiver estimates delay, τ) with the transmitted version.

Regenerating the PN code at the receiver is easily done by following the steps specified in the standard specifications. Synchronization of the code and finding τ proves to be a bigger challenge. The synchronization is performed by “sliding correlators” that will constantly asssurethat the codes used are synchronized.

The multiplier output yields the desired data signal bi(t - τ) plus interfering terms due to other users. Ideally, the integrator, an integrate and dump over Tb seconds, should produce a cross-correlation between the desired signal and the interferers that is 0. Hence, the output for traffic channel i is proportional to the transmitted data stream, bi(t - τ).

CL8300-SG.en.UL 108



Summary

• High code-correlation means the codes are very similar.• CDMA uses three codes:

– Long code• Masked with a long code mask

– Short code• Can be shifted to create PN offsets

– Walsh code• Generated using the Hadamard matrix• Have to be orthogonal

• The codes are used for scrambling and spreading.– The receiver knows the set of codes used for the user in question

• Digital modulation• Receiver performs signal processing steps in reverse.

A fundamental part of a CDMA system are the codes used in spreading and scrambling of the information signal. It is important that the codes have good correlation characteristics, i.e., high correlation with the same code, and low correlation with other codes. Three codes are used in the CDMA systems discussed in this course: long code, short code, and Walsh code.

The long code is used when there is a need for a user-specific code. The user-specific code is obtained by masking the long code with a long code mask that is unique to every user or channel.

The short code is actually two codes, one for the I-phase, and one for the Q-phase components of the RF signal. The short code is used for spreading/scrambling. By applying a time shift to the short code, PN offsets are generated. A PN offset is used to identify a base station’s antenna face.

Walsh codes are generated using a Walsh function. The Walsh function uses the Hadamard matrix when generating Walsh codes. An important characteristic of the Walsh codes is that thecodes are orthogonal. Walsh codes are often used to separate channels transmitted within the same CDMA Channel.

When a receiver knows the codes used for a specific user, the receiver can extract that user’s information from the CDMA Channel.

A quadrature mixer generates the I-phase and Q-phase components of the RF signal. The information (energy) on the two phases is determined in the digital modulation step. BPSK and QPSK were shown as examples of digital modulation. Other digital modulation techniques will be discussed throughout the course.

When the transmitted signal is received at the receiver, all the signal processing steps must be performed in reverse order to extract the original information signal.

CL8300-SG.en.UL 109



Knowledge Check

1. Using the Hadamard matrix, what does W1216 look like?

A. 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0

B. 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1

C. 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1

D. 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1

2. What Walsh codes of length 2, 4 and 8 are notorthogonal with W12

16 and why?A. W0

2, W12, W0

4, W24, W0

8, W48

B. W12, W0

4, W24, W0

8, W48

C. W02, W0

4, W08, W4

8

D. W02, W0

4, W48

CL8300-SG.en.UL 110




3. The shift register circuit shows a maximal-length shift register, if the registers are initialized with 1 0 0 0.

A. TrueB. False

4. What is the periodicity (in chips) of the code generated by the shift register shown in Question 3?A. 4B. 6

C. 7

D. 15

1 2 3 4

+ Output

Clock 1 2 3 4 OutputRegister

Clock 1 2 3 4 OutputRegister

CL8300-SG.en.UL 111




5. PN(t) is a 15 bit code as shown below. What is the correlation value between PN(t-1) and PN(t-6)?

A. -14/15B. -1/15

C. 0

D. 1

PN(t)

-1

0

1

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6. What is the difference between PN offset 41 and PN offset 42?A. Different codes

B. 1 bit

C. 64 bitsD. 512 bits

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Lesson 5CDMA Concepts

CL8300-SG.en.UL 114



Lesson Objectives

• Differentiate between RF impairments• Explain the functionality of the Rake receiver• Describe the random access procedure• Describe the soft handoff process• Explain the benefits of power control• Explain the impact of system loading on coverage.

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5.1 RF Impairments - Delay Spread

• Multipath– Reflected signals

• Delay spread– Typically a few

micro seconds depending on area

• CDMA solution– Rake-receiver

– Search windows.

Base StationAntenna

1

2

3

4

t1 t2 t3 t4

TMMultipleReceivedPulses

Delay Spread

Multipath and Delay Spread

Multipath is a phenomenon that occurs when an RF transmission strikes a solid object (such as a building, vehicle, etc.) and is reflected. The reflections may turn the signal away from its intended path, they may cause the signal to be scattered, or they may direct the signal toward another reflector. Eventually, the radiated signal reaches a receiving antenna, arriving from several different directions. This is the basis of multipath.

In CDMA systems, multipath can be either an advantage or disadvantage. When multipathsignals arrive within approximately 4 msec of each other, they can be used to maintain a low frame error rate (FER). If the multipath signals arrive with a delay of greater than 4 msec, they can be damaging to the received signal.

The signal received at the receiver from the transmitter is made up of the sum of many signals, each traveling over a separate path. Because these path lengths are not equal, the information carried on the radio link will experience a spread in delay as it travels between base and mobile. In the illustration, a transmitted narrow pulse arrives as four pulses, where the delay spread is defined as TM. Typical delay spreads are from 2-5 µs in urban areas. However, delay spreads of around 25 µs has been seen in large distant buildings such as apartment flats.

The effect of delay spread can be reduced, or eliminated using Rake receivers and search windows. A search window defines a window in time, in which the Rake receiver’s fingers will decode the multipath components.

CL8300-SG.en.UL 116



RF Impairments - Rayleigh Fading

• Multipath signals added constructively and destructively at receiving antenna– Called Rayleigh fading

– Received signal follows statistical model• 10 dB below the local mean in 10 percent of the locations• 20 dB below the local mean in 1 percent of the locations

• CDMA solution– Power control

• Slow fading

– FEC encoding and interleaving• Fast fading

– Wide-band carrier.

Rayleigh Fading

In addition to delay spread, the same multipath environment causes severe local variations in signal strength as these multipath signals are added constructively and destructively at the receiving antenna. This type of variation is called Rayleigh fading. Statistically, the received signal will be 10 dB below the local mean in 10 percent of the locations, and 20 dB below the local mean in 1 percent of the locations. This can cause large blocks of information to be lost.

If the set of reflected signals have one dominant component, such as a line-of-sight signal, the fading is more appropriately modeled using the Rician model.

Note that if the mobile speed is zero, there is no fading, except if signals are reflected from moving objects.

For slow fading, CDMA uses power control to adjust the transmitted power in order to overcome the fades. Power control is too slow for the fast Rayleigh fading; instead, FEC encoding and bit interleaving are used.

By having a wide-band CDMA carrier, narrow frequency-selective fading will have limited impact on the signals.

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RF Impairments - Doppler Shift

• Movement of mobile creates a Doppler shift– Received signal shifted in frequency/phase as a function of

direction and speed

– Shifts as much as ±100 and ±200 Hz can take place at 900 MHz and 1800 MHz, respectively

• CDMA solution– Pilot signal for synchronization and channel estimation

– Continuous track of each signal.

Doppler Effect

The third effect of multipath propagation is caused by the movement of the mobile station. This effect is known as Doppler shift and causes each receive signal to be shifted in frequency as a function of the direction and speed of the mobile. Shifts of as much as ±100 and ±200 Hz can take place in cellular systems at 900 MHz and 1800 MHz, respectively. As a result, differential detection techniques must be used to demodulate the received signal. The maximum Doppler shift occurs when a wave is coming from the opposite direction as the direction to which the mobile is moving.

A pilot signal is used by the receiver to track the signal, estimate the condition of the channel, and synchronize to the changing signal.

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Path Loss and Shadow Fading

σ = 8 dB

Distance (R)

Signal strength [dBm]

d1 10 * d1

38.4

dB

In typical cellular radio frequencies, there are two types of signal strength variations:

•Microscopic variations

•Macroscopic variations.

The microscopic (short term) variations are known as Rayleigh fading and take place as the mobile station moves over a short distance compared to the distance between mobile station and base station. Rayleigh fading is discussed in the course.

Path Loss

Macroscopic variations can be modeled as the addition of two components that make up the path loss between mobile station and base station antennas. The first component is a deterministic component, L (red dotted line), that adds loss to the signal as the distance, R, increases between the base station and the mobile station. This component typically can be written as:

L = 1 / Rn

where n is about 3.84, depending on the RF environment. In dB, this component contributes to a roll-off of about 38.4 dB per decade of distance; i.e., L [dB] = 38.4 * log(R).

Shadow Fading

The other macroscopic component is a random variable, X. X follows a log-normal distribution with a mean of 0 dB and a typical standard deviation* of 8 dB (blue dashed line). This random component takes into account the effects of shadow fading caused by variations in terrain and other obstructions in the radio path. When added to the deterministic component, we get a “local mean” value of path loss which, when subtracted (in dB) from the radiated transmitted RF power, yields the received power to the mobile antenna.

When designing the system from an RF perspective, a margin for shadow fading is included in the design. Power control is also useful against shadow fading.

* Given the mean value, m, and the standard deviation, σ, with a log-normal distribution, 67% of the values are within the range [m - σ, m + σ].

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5.2 Rake Receiver

• What is a Rake receiver?– A Rake receiver has a number of fingers

– Each finger locks on to a multipath component

– The signals from each finger are combined

– A searcher constantly searches for the best multipath component.

Combine& Decide

b1(t)

Tx

cos ωctC1 (t - ∆N)

C1 (t - ∆2)

C1 (t - ∆1)

Holduntil

Tb + ∆N

Integrate& dump

Tb second

Holduntil

Tb + ∆N

Integrate& dump

Tb second

Integrate& dump

Tb second

Holduntil

Tb + ∆N

path 1

path 2

path N

.:

.: .

:.:

∆i = differential delay betweenpath i and system time∆i = differential delay betweenpath i and system time

The receiving antenna uses a Rake receiver with a number of fingers that are tuned to the incoming signal. Each finger receives the signal from a different path based on signal strength. Inside the receiver, the received signals are compared and correlated. Errors in a frame received on one finger of the Rake receiver may not appear on the same frame received on one of the other fingers. Using all frames received on all fingers, the receiver can rebuild the frame for improved call quality. The combining is often maximum ratio-combining.

In some cases, however, multipath can appear as interference to the received signal. In those cases, the propagation delay is so great that the received frame cannot be used to reconstruct the frame received on the other fingers of the rake receiver. This situation is less common than whenmultipath is advantageous to the CDMA system. Other technologies are unable to take advantage of multipath because they do not use rake receivers.

A “searcher” constantly seeks different multipath components. The fingers are used to tune to frames being received from different directions. As described earlier, the received frames from the different fingers are compared to one another and can be used to reconstruct missing bits in a frame caused by interference.

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Quadrature Despreading And Rake Receiving

Tb

0

∫

Hold

Path 1

sin (ωct + φ)

QuadratureDespreading

cos (ωct + φ)

PN-I(t - ∆1)

QuadratureDemodulation• • •

Hold

Tb + ∆1

PN-I(t - ∆j)

PN-Q(t - ∆1)

PN-Q(t - ∆j)

Path J

Tb

0

∫

Decide

b1 (t)I

Q

Tb + ∆j

.

.

.

A Rake receiver takes advantage of the multipath environment to improve receiver performance. Rake receivers are needed in both transmission directions.

Shown is the Rake receiver for a user. The receiver sums the demodulated I and Q signals for each path. The differential delays are measured by the receiver in order to accomplish this. The sum for each path is integrated, and then the results from all paths are summed to produce the stronger signal.

The Rake receiver can resolve as many paths as it has rake fingers (minus the searcher). Individual path arrivals are tracked independently, and the weighted sum of their received signals is then used to detect the signal.

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5.3 CDMA Call Processing Overview

Power On

Traffic ChannelState

AccessState

IdleState

InitializationState

In order to realize the benefits of CDMA, an understanding of the fundamental CDMA call processing steps are needed. A mobile station can be said to have four mutually exclusive call processing states: Initialization State, Idle State, Access State, and Traffic Channel State.

Initialization State

When a mobile station (or access terminal) first power on, the mobile station initializes itself. The Initialization State is needed so that the mobile station can align itself to the system’s CDMA codes and timing. Information about synchronization and timing is sent from the base station on an overhead channel, e.g., Sync Channel in IS-95 and IS-2000.

Idle State

After the Initialization State, the mobile station enters the Idle State. In the Idle State, the network can communicate with the mobile. An overhead channel is used to communicate with the mobile station; the overhead channel can be the Paging Channel for IS-95 and IS-2000, to the Control Channel for IS-856.

A mobile station monitors the overhead channel for a page message. The page message informs the mobile to initiate contact with the network, a termination. The mobile station may also decide to initiate contact with the network without receiving a page message, an origination. The contact is done in the Access State, on an Access Channel, and called an access attempt.

If a data session (virtual connection) is established, the Idle State is called the dormant state.

Access State

When the access attempt is successful, the base station sets up and assigns a Traffic Channel for the mobile. The Traffic Channel assignment is communicated to the mobile using a forward overhead channel, e.g., Paging Channel for IS-95 and IS-2000.

Traffic Channel State

In the Traffic Channel State, user data is exchanged. Also, the mobile station performs a number of call processing activities such as handoff and power control.

Next, we discuss random access, handoff, and power control in more detail.

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5.4 Random Access

• Access protocol– Based on a slotted aloha protocol

• Used when mobile contact base station– Quickly

– Avoid interference

• Trial-and-error– Probes sent on reverse Access Channel

– Acknowledgement transmitted on Paging or Control Channel

– If no acknowledgement received, power is increased and another probe is sent.

A mobile may attempt to access a base station whenever the mobile needs to communicate with the base station; I.e., if the mobile originates a call or if the mobile has been paged by the system. The access attempt is performed in the Access State.

The mobile transmits a message to the base station on the Access Channel using the Access Channel Protocol. The message is sent in an access probe, which is sent during an access channel slot.

The access channel slots are non-overlapping. Collisions are avoided using a very narrow demodulation window. Access probe consists of a preamble portion and a message portion.

The Access Channel Protocol specifies the rules with which the access probes are transmitted on the Access Channel.

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Access Procedure

… … …

IP

PowerStep

tP

tS

PersistenceTest

Probe 1 2 3 NP 1 2 3 NP

Sequence 1 2 NS

Time

…

IP = - Mean Rx Power (dBm) + Various AdjustmentsIP = - Mean Rx Power (dBm) + Various Adjustments

Introduction

The mobile accesses the base station on the Access Channel using a random procedure to minimize the chance of interference to other users. The access protocol is controlled by base station-controlled parameters that are communicated to the mobile. The figure shows a simplified Access Channel Protocol as first introduced in IS-95A.

Access Attempt

The entire process of accessing a base station is called an access attempt. Each transmission in the access attempt is called an access probe. The mobile transmits the same data in each access probe in the access attempt.

Within an access attempt, access probes are grouped into access probe sequences. Each sequence consists of a number of access probes, all transmitted on the same Access Channel. The first access probe of each sequence is transmitted at a specified power level relative to the received signal’s power level, IP. Each subsequent access probe is transmitted at a higher power level until the base station acknowledges the transmission.

To avoid the risk of collisions of access probes at the base station receiver, the time of transmission of the probes is randomized.

Persistence Test

A persistence test may take place before the transmission of each access probe sequence. The purpose of the persistence test is to increase the probability a high priority subscriber will gain access over a lower priority subscriber during emergency or overload conditions.

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Access Probe

… … …

Access Probe

tS

PersistenceTest

Probe 1 2 3 NP 1 2 3 NP

Sequence 1 2 NS

Time

…

Preamble Segment Message Segment

Access Probe Structure

The actual access probe transmission consists of a preamble segment, followed by the actual message segment consisting of a number of frames. The preamble is used to synchronize the base station to the mobile. The preamble plus the message capsule is called one access slot.

Note: IS-856 uses the concept of Access Channel Cycles instead of access slot. While the concept remains the same, an Access Channel Cycle does not have to be the length of the preamble plus the message.

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Limitations Of IS-95A Access Procedure

• Procedure used in IS-95A has limitations:– Data rate of 4.8 kbps

• Slow data rate, so message duration is long

– Long preamble segment typically used • Low throughput and relative large delays

– If error occurs for message:• Retransmission at higher power• Increased latency

– More transmit power needed for error-free message• More interference reduces system capacity

• Later technologies improve the access scheme.

The presented access procedure is used in IS-95A. The procedure has limitations.

First, the data rate of the IS-95 Access Channel is 4.8 kbps. This data rate is a low data rate; therefore, the messages transmitted are long in duration.

The preamble segment in the access probe must be relatively long so that the base station receiver can properly detect the message segment. This leads to a low throughput on the Access Channel, and relatively large delays. Low throughput and large delays are not desirable since the probability of an access message being received in error at the base station is increased.

If an access message was received in error at the base station, it will be retransmitted with a higher power level. Not only will this retransmission increase the latency of the message, but the increased power will increase the interference seen in the system. Increased interference decreases system capacity.

Later technologies, e.g., IS-95B, IS-2000, and IS-856, introduce enhancements to the IS-95A access procedure that decreases the probability of an access message being received in error.

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IS-95B Access Handoff Features

95A 95B 3G 1xEVMobile (MS) idle

Access EntryHandoff

MS performs access attempt.

Origination?

Yes

No

AccessHandoff

MS has trafficchannel

Channel AssignmentInto Soft HandoffChannel AssignmentInto Soft Handoff

Access ProbeHandoffAccess ProbeHandoff

Additional technology specificimprovements exist. See thespecific lessons for more details.

Additional technology specificimprovements exist. See thespecific lessons for more details.

BS pages MS

Introduction

IS-95B introduced a set of features aimed at lowering the origination and termination failures by increasing the efficiency of the access scheme. The features assure that the mobile is always communicating with the best server or servers. The features are:

•Access Entry Handoff

•Access Probe Handoff

•Access Handoff

•Channel Assignment Into Soft Handoff

The Access Handoff features operate from the time the base station sends a page message to the mobile, until a Channel Assignment Message is sent to the mobile.

Access Entry Handoff

Access Entry Handoff (AEHO) allows mobiles to transfer the reception of the paging channel from one base station to another before the mobile transmits access probes during a termination.

Access Probe Handoff

Access Probe Handoff (APHO) allows mobiles to handoff to a stronger CDMA pilot while waiting for acknowledgement to the access probe.

Access Handoff

Access Handoff (AHO) allows mobiles to transfer reception of the paging channel from one base station to another after a successful access attempt. When a mobile sends a message to a cell and receives an acknowledgment from the cell, a successful access attempt has been made.

Channel Assignment Into Soft Handoff

Channel Assignment Into Soft Handoff (CAMSHO) gives the capability for a mobile to request multiple traffic channels with multiple cells (soft handoff) when the traffic channel assignment takes place.

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5.5 Soft Handoff

MSC

Base Station B

Base Station A

Soft handoff is a term used to describe a feature unique to CDMA systems in which a mobile can be in communication with two or more base stations, or antenna faces, simultaneously. Other wireless technologies such as FDMA and TDMA use hard handoffs between base stations. The hard handoff involves both a change of base station and a change of frequency. As a result, the mobile must break its connection with the serving cell, tune its receiver to the new serving cell’s frequency, and resume the call.

Because CDMA typically involves only one frequency, the mobile is able to monitor and communicate with multiple base stations simultaneously. This allows the mobile station to make its connection with the new base station while still communicating with the serving base station.

A CDMA mobile station is said to be in soft handoff when the mobile communicates with two or more antenna faces (PN offsets). The PN offsets involved in soft handoff are said to be in the mobile station’s Active Set. Up to six PN offsets can be in the active set. The traffic frames from the various antenna faces are sent to the MSC, where the best frames are selected.

The soft handoff process enables the mobile to establish contact with those sectors likely to proceed well before it leaves its serving (host) site. In addition, the simultaneous support provides a diversity gain that improves link quality in “fringe” areas, and multipath is taken advantage of with the rake receiver. The application of power control from neighbor sites also ensures that a progressively distant mobile will not unduly boost its transmit strength and become a primary source of interference to a nearby cell site.

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Softer Handoff

Base Station

Rake Receiver

TrafficFrames

αβ

MSC

Speech Handler

A subset of soft handoff is the so-called softer handoff. A softer handoff occurs between two sectors of the same cell.

Softer handoff is a special case of soft handoff and can be handled within the base station by one channel element (CE) saving resources. The CE is typically the component in the base station that performs most of the digital processing of the information signal.

A softer handoff occurs when the mobile moves between cell sectors. The mobile is in a soft handoff mode, since it is communicating on two CDMA Traffic Channels in the same 1.23MHz CDMA RF Channel. The base station can use the CE’s rake receiver to combine the traffic frames from both sectors into a single traffic frame that is sent to the MSC.

The MSC treats this traffic frame as if it were the only frame received by the base station CE. The base station CE also generates two forward traffic channel frames, each with a different Walsh code.

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Soft/Softer Handoff Process

• Mobile Assisted Handoff based on pilot signal levels of neighboring base stations

• Three phases:– Measurement

• Mobile measures signal quality and strength• Mobile sends a message when add/drop threshold are met

– Trigger• Base station evaluates measurements against threshold• Base station decides if handoff should be initiated

– Transition• Base station tells mobile what base stations to communicate with• Mobile enters the soft handoff state (intra-frequency handoff)

– or an inter-frequency handoff is performed.

Measurement

During the measurement phase, the mobile takes measurements of the signal quality and signal strength of its serving cell or cells and its neighboring cells. The mobile measures the Ec/I0 of the pilots and reports the signal strengths to the base station.

An IS-95 and an IS-2000 mobile reports the signal strength in the Pilot Strength Measurement Message, and an IS-856 mobile (Access Terminal) reports the signal strength in the RouteUpdateMessage.

Trigger

The measurement results are compared against thresholds and defined rules. The base station decides whether handoff should be initiated. Also, the base station determines what type of handoff that will take place: Soft handoff, softer handoff, or an inter-frequency handoff (between carriers).

Transition

If a handoff is triggered, the base station orders the mobile to execute the handoff by starting to communicate with the new antenna faces, or to stop communicating with the antenna faces that have fallen out from the handoff state.

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Pilot Sets and Handoff Parameters

• Pilots in four mutually exclusive sets– Active Set

– Candidate Set

– Neighbor Set

– Remaining Set

• Pilots move between these sets based on handoff parameters and rules– Base station controls Active Set and Neighbor Set

• Four handoff parameters– Add threshold (t_add)– Drop threshold (t_drop)

– Drop timer (t_tdrop)

– Comparison threshold (t_comp).

For a given mobile, the pilots (PN offsets) are organized into four mutually exclusive set that are controlled by a number of handoff parameters and specific rules.

Active Set

The pilots actively involved in soft/softer handoff are placed in the Active Set. The base station instructs the mobile what pilots to have in the Active Set.

Candidate Set

Pilots that satisfy the criteria to be included in the Active Set, but have not yet been added are placed in the Candidate Set.

Neighbor Set

Pilots that are likely candidates for soft/softer handoff will be in the neighbor Set. The Neighbor Set is controlled by the base station and are usually base stations whose geographical coverage areas are near the mobile station.

Remaining Set

The pilots not included in all other sets are parts of the Remaining Set.

Add Threshold

A pilot must be stronger than the add threshold to possibly be added to the Active Set. The add threshold is called t_add in IS-95 and IS-2000.

Drop Threshold and Drop Timer

A pilot weaker than the drop threshold for a longer time than the drop timer will be removed from the Active Set. The two thresholds are called t_drop and t_tdrop, respectively, in IS-95 and IS-2000.

Comparison Threshold

The comparison threshold is used to make sure that a pilot in the Candidate Set is a certain amount stronger than a pilot in the Active Set before replacing that Active Set pilot. The threshold is called t_comp in IS-95 and IS-2000.

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Original Soft Handoff Algorithm -Example

Add Threshold

Drop Threshold

Pilot 1(BS1) Pilot 2

(BS2)Active SetTotal Ec/I0

Signal Strength

Time

BS2 addedto Active Set

BS1 removedfrom Active Set

Soft Handoff Range

DropTimer

1

2

3

Example

The graphic shows the handoff parameters when the signal strength of base station 2 (BS2) exceeds the add threshold (point 1), and the pilot enters into the mobile’s Active Set. When the signal strength of base station 1 (BS1) falls below the drop threshold (point 2) and stays there until the drop timer has expired (point 3), BS1 is removed from the Active Set.

Note that add threshold and drop threshold are fixed and do not take into account situations where a weak pilot added to the Active Set would not bring any benefit if there are already some dominant strong pilots in the Active Set. Adding a weak pilot does not improve performance. However, if all pilots in the active set are weak, then even adding a new weak pilot is beneficial.

Soft Handoff Gain

In a CDMA system, there is an advantage due to soft handoff that results in effectively lowering the fade margin required to obtain a specific probability of edge coverage, as compared to other technologies. For a CDMA system that admits soft handoff, for any given frame, the better or stronger of two or more base stations’ reception will be utilized at the frame selector, typically at the switching center.

Assuming an 8 dB standard deviation and 50% partially correlated two-way handoff, the soft handoff gain numerically works out to approximately 4 dB. Due to the soft handoff feature, the excess link margin requirement has dropped by 4 dB. This is the advantage due to soft handoff that results in increased coverage.

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IS-95B Soft Handoff Algorithm

• IS-95B Soft Handoff algorithm– Reduce soft handoff activity

– Filter out unnecessary handoffs

– Reduce number of soft handoff legs

– Improve forward link capacity

• Additional soft handoff parameters– Soft Slope

– Add Intercept

– Drop Intercept

• Dynamic thresholds calculated– Dynamic Add Threshold (DAT)

– Dynamic Drop Threshold (DDT)

– Based on the Ec/I0 of the Active Set.

PSi

Ec/I0

Background

The field data shows that under some conditions, there may be more soft handoffs occurring than are necessary when using the original IS-95A handoff algorithm. Such handoff overheads may also overuse system resources, thereby degrading total system capacity. The IS-95B soft handoff algorithm is intended to improve these situations by introducing the Dynamic Add and Drop Thresholds (DAT and DDT, respectively).

DAT and DDT are determined by combining the pilot strengths from all pilots in the Active Set. Under this algorithm, the mobile will send out a message with pilot signal strength measurements to request the base station to add a pilot into the Active Set only when the pilot is worthy of being added. The mobile will request the base station to drop a pilot from the Active Set if the pilot contributes little to the call quality.

Benefits

The IS-95B soft handoff algorithm introduces improvements that will reduce the time a call is in soft handoff, and also filter out unnecessary handoffs from each call; therefore, the average number of legs for each call is reduced and the forward link capacity is increased.

Dynamic Thresholds

Three additional parameters are defined for IS-95B; namely, an Add Intercept, Drop Intercept, and a Soft Slope. The parameters contribute to the calculation of the DAT and DDT.

+

= ∑

∈b_add_t,cptint_addPSlog*10*slope_softmaxDAT

APS:ii

i

+

= ∑≥∈

b_drop_t,cptint_dropPSlog*10*slope_softmaxDDT

ji

iPSPS

,APS:iij

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IS-95B Soft Handoff Algorithm - Example

Add Threshold

Pilot 1(BS1) Pilot 2

(BS2)Active SetTotal Ec/I0

Signal Strength

Time

BS2 addedto Active Set

BS1 removedfrom Active Set

Original Soft Handoff Range

DropTimer

23

4

Drop Threshold

Soft Handoff Range

1

DynamicAdd Threshold Dynamic

Drop Threshold

5

The figure shows a time representation of soft handoff and associated event when the mobile moves away from a serving base station (BS1) towards a new base station (BS2). The combination of static and dynamic thresholds (vs static thresholds only) results in reduced soft handoff regions.

The principles of the Dynamic Add Threshold (DAT) and the Dynamic Drop Threshold (DDT) for adding and deleting pilots are as follows.

The mobile detects a pilot which crosses a given static threshold, the Add Threshold [Ec/I0] (point 1). The pilot is then moved to the Candidate Set and is searched more often and tested against a second dynamic threshold, DAT.

Comparison with DAT determines if the pilot is worth adding to the active set. DAT is a function of the total energy of the pilots demodulated coherently (in the Active Set).

When the pilots in the Active Set are weak, adding an additional pilot (even weak) will improve performance. However, when there are one or more dominant pilots, adding an additional weaker pilot above the Add Threshold will not improve performance, but will use more network resources. The dynamic soft-handoff thresholds reduce and optimize the network resource utilization.

After detecting a pilot above DAT (point 2), the mobile reports it back to the network. The network then sets up the handoff resources and orders the mobile to coherently demodulate this additional pilot.

When a pilot signal strength decreases below DDT (point 3), the handoff connection is removed after a specific period (point 4). The pilot is moved back to candidate set. The threshold DDT is a function of the total energy of the other pilots in the Active Set. Pilots not contributing sufficiently to total pilot energy are dropped. On further decreasing below a static threshold, the Drop Threshold, the pilot is removed from Candidate Set (point 5).

A pilot dropping below a threshold (e.g., DDT and Drop Threshold) is reported back to the network only after being below the threshold for a specific period. This timer allows for a fluctuating pilot not to be prematurely reported.

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Inter-Frequency Handoff

• Inter-frequency handoff is a handoff between carriers– Maximize resource utilization

– Congestion control

– Inter-operator handoff

• Base station controlled inter-frequency handoff– Most common type of inter-frequency handoff– Uses vendor specific algorithms at the base station

• Mobile assisted inter-frequency handoff– Mobile makes pilot measurements on other carriers

– Message used to report pilot signal strengths can include pilot’s channel number and band class

– Not specified for IS-95A.

Intra-frequency handoff (soft handoff) is the handoff between base stations when the same carrier frequency is used. Inter-frequency handoff is the handoff between carrier frequencies. When performing an inter-frequency handoff, the mobile station must discontinue the transmission on the current carrier while it retunes to a new Traffic Channel on the new carrier.

There are many reasons why inter-frequency handoffs are performed:

•We want to maximize the utilization of resources on each carrier

•If the current carrier experiences resource congestion, the mobile station could handoff to another carrier to ease the situation

•The mobile station may have to handoff to another operator, so-called inter-operator handoff.

Most inter-frequency handoffs are controlled by the base station, without any explicit assistance from the mobile. Since the base station controls the handoff, the algorithms used are proprietary to the vendor.

When the mobile station assists the base station in the inter-frequency handoff, we call this mobile assisted inter-frequency handoff. The mobile station may have the capability to make pilot signal strength measurements on other carriers. The mobile can then report these measurements to the base station, including the pilot’s channel number and band class.

Note: An IS-95A mobile station cannot report a pilot’s channel number and band class..

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Mobile Assisted Inter-Frequency Handoff

• A mobile may be allowed to make pilotmeasurements on other frequencies while maintaining connection with the current frequency

• Two methods for mobile assisted inter-frequency handoff:– Dual receivers at the mobile

• Not specified in the standard

– Mobile visits candidate frequency for a short period as commanded or periodically to make measurement

• Base station may direct mobile to new frequency based on measurements

• Mobile is allowed to return to previous frequency in case of failure• Not specified for IS-856.

95A 95B 3G 1xEV

Two methods may be used for mobile assisted inter-frequency handoff: Dual receiver, or a single receiver operating in “slotted mode” (mobile visits the candidate frequency for a short time period).

The dual receiver approach is suitable if the mobile terminal uses antenna diversity. During the inter-frequency measurements, one receiver branch is switched to another frequency for measurements, while the other keeps receiving from the current frequency. The loss of diversity gain during measurements needs to be compensated for the higher forward link transmit power. The advantage of the dual receiver approach is that there is no break in the current frequency connection.

The slotted mode approach is considered attractive for the mobile station without antenna diversity. The mobile visits another frequency during a short period of a frame to make a measurement of the other frequency’s pilot signal strength.

After a measurement, the mobile may send the information to the base station in the regular message used to report pilot signal strengths. The message can include the pilots’ channel numbers and band classes. The base station still makes a decision and can order the mobile to continue the call on a new carrier frequency. If there is a failure for the mobile going to the new frequency, the mobile may be allowed to return to the original serving frequency.

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5.6 Power Control - Near/Far Problem

MS 1

A1

MS 3

MS 2

MS 4

A3

A2

A4

reverse link interference

for MS 1

• Near mobiles dominate:— Signal-to-interference ratio is lowered for far mobiles— Performance is degraded for far mobiles— System capacity is reduced

• The problem can be reduced through mobile dynamic power control to equalize thereceived signal levels:

A1 = A2 = A3 = A4

A power control problem arises because of multiple access interference. All users in a DS-CDMA system transmit information by using the same bandwidth at the same time, and therefore, users interfere with one another. The signal received by the base station from a mobile close to the base station will be stronger than the signal received from another mobile station located at the cell edge.

Near/Far Problem

The near/far problem is concerned with a strong interferer at a receiver swamping out the effects of weaker signals. This can occur in the cellular environment when a mobile unit close to the base station masks the received signal from far-end mobiles.

This problem can be resolved through power control. For a CDMA cellular system, this requires that the power transmitted from the mobiles to the base station be adoptively controlled. When the transmitted power from each mobile is controlled so that all received signals arrive with equal power at the base station, (A1 = A2 = A3 = A4) then system capacity is maximized for a specified signal-to-interference ratio.

It is important to remember that one mobile's signal is another mobile's interference.

Forward Link

In the forward link, all signals propagate through the same channel, and thus are received by a mobile with equal power. Therefore, no power control is needed to solve the near-far problem for the forward link. However, power control is required to minimize the interference to other cells and to compensate against the interference from other cells. The worst-case situation for a mobile station occurs when the mobile station is at the edge, equidistant from some number of base stations.

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Desired Mobile Power Control

80

dB Rel

ativ

e B

ase

Sta

tio

nR

ecei

ved

Pow

er8 dB variationabout the average(log-normal shadow fading)

km

dB

Rel

ativ

e M

obile

Tra

nsm

it P

ow

er

dB

km

Rel

ativ

e P

ow

er a

tM

obile

Rec

eive

r1

R3.84Average Path Loss

km

The power transmitted by the mobile is based on a measurement of the received power. This measurement accounts for path loss and shadow fading. As shown, the mobile transmit power varies inversely with the received power. The base station will then receive an almost constant level of signal. This type of control is called open loop power control since there is no feedback between mobile and base station.

In addition, the base station will send power control commands to direct the mobile to adjust its power. The power control commands are chosen such that the base station receives an acceptable frame error rate for that particular traffic channel. This type of control is called closed loop power control since there is feedback between mobile and base station.

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Why Power Control?

• Objectives:– Maintain QoS

– Maximize capacity

– Minimize interference

• Power control algorithms– Forward Link Power Control

• Discussed in each specific technology section

– Reverse Link Power Control.

The nature of CDMA systems is such that interference is one of the primary problems which may affect communications. With all of the base stations and mobiles operating on the same frequency at the RF noise floor, controlling the interference is essential.

The fundamental purpose of power control is to maintain acceptable Quality of Service (QoS) for the largest number of users. Service providers identify the following as the objectives for power control:

•Maintain satisfactory QoS

•Maximum system capacity consistent with the QoS objective

•Minimum power consumption for both the battery powered mobile and the base station transmitters.

To achieve the objectives, two types of power control are needed:

•Forward Link Power Control

•Reverse Link Power Control.

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Reverse Link Power Control

• Transmit just enough power to achieve required Eb/N0

• Open loop power control– Compensate for path loss and shadow fading

– Operates at the mobile station

• Closed loop power control– Improves inaccuracies in the slower open loop power control– Operates at the base station.

Receivedsignal

PCB

Matchedfilter

Rakecombiner

Viterbidecoder

Inner loopcontrol

Outer loopcontrol

Eb/N0

MeasurementFrame error

detector

Open Loop Power Control

Open loop power control sets the transmit power based upon the power that is received at the mobile. The purpose is to compensate for the path loss from the mobile to the base station and to handle very slow fading.

Closed Outer Loop Power Control

Closed loop power control compensates for medium to fast fading and for inaccuracies in open loop power control. The close loop power control consists of two parts, an inner loop and an outer loop. The outer loop power control is implementation-specific, but typically adjusts the closed loop power control threshold in the base station in order to maintain a desired frame error rate.

Closed Inner Loop Power Control

The inner loop power control consists of a fast feedback loop from the base station to the mobile. The inner loop adjusts the transmit power of the mobile by transmitting power control commands, or bits.

Possible Implementation

The graphic shows a possible implementation of the reverse link power control at the base station. The matched filter and Rake combiner will extract the information bits.

The Viterbi decoder can be used to decode encoded data streams, and the frame error detector can determine is a frame is in error or not. Based on frame errors the outer loop control can set proper operating Eb/N0 at base station receiver. The Eb/N0 determined by the outer loop control is used by the inner loop control.

Current received Eb/N0 is measured and compared with the operating Eb/N0 setpoint, or target Eb/N0, from the outer loop control. Based on the comparison, the inner loop control decides the value of the power control bit (PCB) to be transmitted.

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Why is Fast Power Control Important?

• Transmit higher than required power– Excessive interference

• Transmit lower than required power– Insufficient quality

• Slow power control

• Fast power control.

Thick green line – required powerThin black line – transmitted powerThick green line – required powerThin black line – transmitted power

Fast power control is important. The faster the power control, the more accurate the transmit power is with respect to the required transmit power. If transmit power is higher than required power, then excessive interference is generated and system capacity reduced. If transmit power is lower than required power, then the quality of the channel is insufficient and performance problems may incur.

Examples of slow and fast power control are shown for a specific required transmit power. It can be seen that with the faster power control, transmitted power is closer to required power, thereby reducing excessive interference while maintaining sufficient quality.

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5.7 Noise Rise vs. Coverage Reduction

Bit energy (Eb )

if mobile transmits

constant power

Distance

Energy seen at BS receiver

At the edge of the cell, the mobile is transmitting max power

At the edge of the cell, the mobile is transmitting max power

Eb/N0

N0 withoutloading

Eb

Cell edge

Noise rise

Eb

N0 withloading

Eb/N0

Newcell edge

Coverage reduction

¤

Noise rise and its impact on reverse link coverage is a very important concept in CDMA. The concept relates mostly to the reverse link.

Base Station Received Noise

The base station receiver receives the RF energy that exists within the receivers bandwith. The information in a traffic channel on the reverse link is extracted by the base stations’s circuits that perform the necessary signal processing. The extracted digital information has some bit energy, Eb. All the other RF energy is considered interference to this particular traffic channel. That interference is suppressed by the processing gain. The ratio between Eb and the noise energy (N0), or interference energy is one of the main quality indicators for a digital traffic channel.

Noise Rise and Coverage

Noise rise is the fact that the amount of noise, or interference, increases. When a mobile experiences noise rise, it must increase its transmit power to maintain the required Eb/N0 ratio at the base station receiver as dictated by a certain QoS. A peculiar situation occurs when a mobile is located at the “edge” of the cell.

At the edge of the cell, the mobile is transmitting maximum transmit power. When the mobile at the edge of the cell experience noise rise, it cannot increase its transmit power. The mobile would have to move closer to the cell to allow the reduced pathloss to maintain the Eb/N0 ratio at the base station receiver; the mobile is still transmitting maximum power. In other words, increased noise levels, noise rise, will reduce the reverse link coverage for a given Eb/N0 ratio.

Sources for Noise Rise

There are several sources for noise rise: Other channels, external noise, and jammers. The most significant source for noise rise is other channels, or other users being served by the system. When the number of users increases, the noise rise also increases. When the number of users increases, we say that reverse link loading increases.

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Reverse Link Loading

20

18

16

14

12

10

8

6

4

2

00 10 20 30 40 50 60 70 80 90

3.0

Percent Loading

NoiseRise(dB)

100

No

ise

Ris

e [d

B]

Reverse link loading, or sector loading, is a measure of the total interference from CDMA sources allowed in the system in reference to the receiver thermal noise. As the number of users in the system increases, the noise rise increases. The median noise rise can be calculated as 1/(1-loading), where loading is defined as the ratio of actual users, m, to the pole capacity, Mmax.

The noise rise increases dramatically as the loading approached the pole capacity. This noise rise is also driven by the loading of neighboring cells (frequency re-use efficiency, or β) and the information data rate (channel activity).

The non-linear behavior can be summarized by noting that the ratio of total power at the base station receiver input to base station noise doubles every time half the remaining pole capacity is used. For example, the ratio increases from 0 to 3 dB when the loading factor increases from 0 to 50%, and it rises from 3 dB to 6 dB when the loading factor increases from 50% to 75%.

Typical loading for IS-95 is 55%, for IS-2000 and IS-856, loading may be increased to 72% due to the general increase in pole capacity.

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Radio Frequency Impairments

Total impairment = Thermal noise } N0

+ Co-channel interference from mobiles served by the same physical antenna face

+ Co-channel interference from mobiles served by nearby physical antenna faces

NT

Thermal noise = N0Total impairment = NT

Although thermal noise, N0, is the easiest radio frequency impairment to quantify, it is not the most important impairment to consider in the engineering of a CDMA system. The thermal noise is the impairment which limits the maximum coverage range of any cell site.

The major source for interference is the co-channel interference coming from mobiles served by the physical antenna face in interest. Another major source for interference is the co-channel interference from mobiles served by nearby physical antenna faces.

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Reverse Link Pole Capacity

• Achieved Eb/N0 at J4 has to be greater than or equal to the required, full rate, median Eb/N0, (di)fullrate. For user i: (Eb/N0)i ≥ (di)fullrate = αidi

( ) iiM

1jjjc

M

2jjjct

biiii0b d

STSTFN

TSNE α≥

αβ+α+

α=∑∑

==

Legend:α Activity Factor β Interference Geometryd Bit Energy Over Noise S Received PowerNt Thermal Noise F Receiver Noise FigureTb Bit time Tc Chip time

Legend:α Activity Factor β Interference Geometryd Bit Energy Over Noise S Received PowerNt Thermal Noise F Receiver Noise FigureTb Bit time Tc Chip time

loading*1NETT

*1

1*

1M

0b

cbair

+

β+α=

Pole Capacity

Pole capacity, Mmax, is the CDMA channel capacity limited only by the mutual interference from all users in both the same and neighboring cells. When deriving the pole capacity, the Eb/N0 for user i is derived; see the first equation. Eb is the bit energy for user i, and N0 is the total impairment user i is experiencing. Assuming that external interference (to the CDMA system) can be ignored, the total impairment consists of:

•Thermal noise (Nt)

•Receiver noise figure (F)

•Interference from users on the same cell (second term in the denominator)

•Interference from users on other cells (third term in the denominator).

The beta factor (β) is an interference ratio relating interference from other cells to interference from the serving cell. Alpha (α) is the traffic channel activity factor (including the reverse link pilot, if applicable).

After some general assumptions, we can solve for M and Mmax. The RF Engineering Guidelines discuss the theoretical details and derivations for M and Mmax.

Air-interface Limit

Mmax implies maximum capacity, and therefore also minimum coverage. To have a practical amount of coverage, the capacity has to be decreased. By multiplying Mmax with a loading factor, the air-interface limit, Mair, is obtained.

Note: The pole point capacity is a theoretical estimation given a set of assumptions. The real life capacity will vary based on the variation in the parameters, and other limitations such as hardware capacity.

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Summary

• Several RF impairments exist:– Delay spread– Rayleigh fading– Doppler shift– Shadow fading

• Rake receiver combats fading• An access procedure on the Access Channel is used for

user device to establish contact with the system• Soft handoff enhances performance

– Pilot sets– Handoff parameters

• Power control combats the near/far problem• Increased reverse link loading decreases coverage.

The RF link between the transmitter and the receiver is impacted by many naturally occurring phenomena. Reflected signals (multipath) can significantly change the signal. Reflected signals arrive at the receiver at different times causing delay spread in the signal. The phase differences of the reflected signals may add or subtract to the final signal; this is called Rayleigh fading. When a user is moving, the frequency of the signal may shift according to the Doppler shift. Finally, obstacles in the RF path create shadow fading (log-normal fading).

A hardware component, called Rake receiver, in the CDMA receiver combats multipath by using Rake fingers to lock onto and decode the multipath components.

When a user establishes contact with the system, the user will use an Access Channel. An access protocol is used as a trial-and-error method to establish contact over the Access Channel.

Soft handoff is a unique CDMA feature that allows a mobile to making a connection with a new base station before breaking the connection with the old base station. This provides a natural diversity gain to the system, and improves RF performance. Decisions about soft handoff are made using measurements of base station pilots. The pilots are divided into four pilot sets: Active Set, Candidate Set, Neighbor Set, and Remaining Set. The pilots move between the sets as governed by handoff parameters.

Power control is used to make sure that every user is received with the same energy level at the receiver, so that one user is not swamping weaker signals. For the reverse link, the base station has a power control algorithm with a Eb/Nt setpoint for the reverse link channel. By comparing measured Eb/N0 with the setpoint, power control bits are transmitted to the mobile, telling the mobile to increase or decrease its transmit power.

As the number of users (loading) increases, a channel at the receiver experiences more noise. This is called noise rise. When the noise rise increases, coverage decreases for a fixed signal quality, and vice versa.

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Knowledge Check

1. How does CDMA combat delay spread?A. Power control

B. Pilot signal

C. Speech encoding

D. Rake receiver

2. How does CDMA combat Rayleigh fading?A. Power control

B. Pilot signal

C. Speech encodingD. Rake receiver

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3. How does the Rake receiver know what multipathcomponents to decode?A. By instructions from the base stationB. By the searcher finger in the Rake receiver selecting the best

multipath for the other fingers to decodeC. By each finger selecting the mutlipath with the lowest BERD. By recognizing the Rake receiver-specific code each multipath is

coded with

4. Why is the access procedure needed?A. To determine the power level needed to communicate with the

base stationB. To power control the Traffic ChannelC. For the base station to send messages to the mobileD. All of the above

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5. The IS-95B soft handoff algorithm may reduce soft handoff activity.A. True

B. False

6. What call processing state will the mobile station enter when the power is turned on?A. Traffic Channel State

B. Access State

C. Initialization StateD. Idle State

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Lesson 6IS-95 Specifics

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Lesson Objectives

• Explain how high speed data is implemented• Differentiate between IS-95 revisions A and B• Explain the signal processing steps for a Traffic Channel• Identify the use of the CDMA codes.

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Outline - 1/4

• Major characteristics– High speed packet data implementation

• Forward link– Channels and coding

• Reverse link– Channels and coding

• Primary and signaling traffic.

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6.1 Major Characteristics

• High capacity wireless technology– Dynamic capacity limits

• Enhanced RF channel performance– Rake receiver

– Soft handoff

• Gated reverse link transmission• Support for 8k vocoders and 13k vocoder

– Rate Set 1 (9.6 kbps)

– Rate Set 2 (14.4 kbps)

• Inherent privacy• Data rates up to 115.2 kbps

– IS-95B only.

The CDMA technology and the commercial application, IS-95, are now well established concepts and technologies. One of the main benefits of CDMA is the dynamic capacity inherent in the technology. By optimizing the system and the hardware and software of the network components, system capacity can be increased.

Compared to other technologies, such as GSM and IS-136 (“TDMA”), the performance of CDMA is enhanced through Rake receivers and soft handoff. Rake receivers allow the receiver to efficiently combat multipath. Soft handoff allows the mobile station to have a seamless connection to the network as the mobile station is moving around within the system.

An IS-95 handset (mobile station) utilizes gated transmission to realize variable rates in the information stream (mostly voice). By gating the transmission, interference is reduced, and the mobile station’s amplifier can be kept relatively simple.

IS-95 supports two different Rate Sets (RS), RS1 and RS2. RS1 supports a maximum data rate of 9.6 kbps over the air-interface. RS1 can be used with 8k vocoders such as the EVRC vocoder. RS2 supports a maximum data rate of 14.4 kbps over the air-interface. RS2 can be used with the 13k vocoder.

There is a degree of privacy inherent in the CDMA technology. By using pseudo-noise codes, an eavesdropper cannot intercept the information without extensive code-breaking computations. Please note that while there is inherent privacy in CDMA, the information is not encrypted. Encryption must be performed prior to the CDMA processing.

Revision A of IS-95 supports data rates up to 14.4 kbps (RS2). Revision B supports data rates up to 115.2 kbps (RS2) by utilizing a number of Supplemental Code Channels (SCCH). The SCCHs are part of the Traffic Channel.

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Improvements With Revision B

• Higher data rates– Up to 115.2 kbps

• Dynamic soft handoff thresholds– Conserves resources

• Access Handoff features– Decreases call setup failures

• Hopping pilot beacon– Simulates multiple pilot beacons.

Pilot beacon Pilot beacon Systemtime

Tx_Duration Tx_Offset

Tx_Period

Revision A of IS-95, IS-95A, was the first commercial implementation of the CDMA technology as a wireless communication system. As networks were deployed, operational experience was gained. This experience led to a revision of IS-95A, revision B (IS-95B). Some of the enhancements in IS-95B are listed below.

Higher Data Rates

By using Supplemental Code Channels, IS-95B is capable of supporting data rates up to 115.2 kbps (RS2) over the air-interface.

Dynamic Soft Handoff Thresholds

In order to conserve system resources and thereby increasing the total system capacity, dynamic soft handoff thresholds can be used to decrease the total amount of soft handoff activity. Dynamic soft handoff thresholds are discussed in the CDMA Concepts lesson.

Access Handoff Features

When the mobile station is in the process of establishing contact with the system using the Access Channel, the IS-95B Access Handoff features can be used to decrease call setup failures. The Access Handoff features are discussed in the CDMA Concepts lesson.

Hopping Pilot Beacon

In some places, a pilot beacon may be needed to aid in inter-frequency handoffs (between carriers). IS-95B defines a hopping pilot beacon. The hopping pilot beacon is transmitted periodically and defined by three parameters, in units of 80 ms:

•Tx_Period - The period between pilot beacon transmissions

•Tx_Offset - The time offset of the pilot beacon transmission from the beginning of the transmission period

•Tx_Duration - The duration of each pilot beacon transmission.

Note: IS-95B networks have not been widely deployed around the world. However, IS-2000 systems support IS-95B functionality.

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IS-95B High Speed Data

IS-95B

IS-95A

BaseStation

1.25 MHz channel

Diversity Receiver

• Fundamental Code Channel (FCH) is aggregated with up to seven Supplemental Code Channels (SCCH) to carry high speed data– Signaling messages are not transmitted on SCCH

• SCCH can operate in either forward or reverse link.

Traffic Channel

FCHSCCH

1

SCCHN

::

The Traffic Channel is used for the transmission of user and signaling information to a specific mobile station during a call. Each Traffic Channel contains one Fundamental Code Channel (FCH) and may contain one to seven Supplemental Code Channels (SCCH). By aggregating up to seven SCCHs, the IS-95B Traffic Channel can achieve data rates up to 115.2 kbps for Rate Set 2 (RS2):

14.4 kbps * (7 + 1) = 115.2 kbps

Signaling is only transmitted in the fundamental data block (FCH) via a blank-and-burst format or the dim-and-burst format. When neither primary traffic nor secondary traffic is available, the supplemental data blocks (SCCH) are not transmitted.

The base station can assign a SCCH for the Forward Traffic Channel, Reverse Traffic Channel, or both. The assignment includes the parameters that control the timing of the SCCH assignment (e.g., starting time and duration), and parameters that control the number of SCCHs which will be used during the assignment (e.g., the number of Reverse SCCHs on which the mobile station may transmit, and the set of Walsh codes on which the mobile station receives Forward SCCHsfor each pilot in the mobile station’s Active Set).

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Outline - 2/4





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6.2 Forward Link Channels - Overview

Paging Channels

FundamentalCode

Channel

SupplementalCode

Channels

Pilot Channel Sync Channel Traffic Channels

Forward LinkChannel

In a CDMA system, each base station sector and carrier has its own forward link CDMA channel. The CDMA channel on the forward link consists of the following channels:

•Pilot Channel (F-PICH) - Used at the mobile station to provide continuous time and phasereference. Each base station transmits the short PN code using Walsh code W0 (all zeros) over the F-PICH with a unique base station timing offset.

•Sync Channel (F-SYNC) - In addition to providing system timing and network identification, the Sync Channel identifies the state of the long PN code so that the generation of the long PN code in the mobile is synchronized with the generation of the long PN code at the base station.

•Paging Channel (F-PCH) - Provides notification of incoming calls to idle mobiles. In addition, the F-PCH may be used to broadcast messages. IS-95 allows for up to seven Paging Channels to be used per forward link CDMA channel.

•Fundamental Code Channel (F-FCH) - Carries speech, low speed data, signaling messages, and control information. For IS-95A, the Fundamental Code Channel is the Traffic Channel. For IS-95B, the Fundamental Code Channel is the Traffic Channel is no Supplemental Code Channels are used.

•Supplemental Code Channel (F-SCCH) - Up to seven SCCHs are used in IS-95B to increase the data rate for a forward Traffic Channel.

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Paging Channel Structure

2047 0 1 ... 15 16

Slot n

1.28 seconds

Minimum length slot cycle of 16 slots

2 ......Paging

Channel80ms

The Paging Channel is divided into 2048 paging slots, each slot is 80 ms. Within the 2048 slots, a slot cycle is defined (minimum length is 16 slots, or 1.28 seconds). The Paging Channel protocol provides for scheduling the transmission of messages to an individual mobile station in an assigned paging slot within each slot cycle. We say that the mobile station operates in the slotted mode. If the mobile station were to continuously monitor the Paging Channel, we say that the mobile station operates in the non-slotted mode.

The slotted mode saves battery life for the mobile station since the mobile can power down some of its circuitry when not monitoring the Paging Channel. The mobile station calculates the paging slot by using the International Mobile Station Identification (IMSI) and the hashing algorithm specified in the IS-95 standard. The base station calculates the same paging slot and only transmits messages to a mobile in that particular paging slot.

The slot cycle is a multiple of 1.28 seconds, and is specified by the slot cycle index. The length of the slot cycle, T, in units of 1.28 seconds is given by:

T = 2i

Where i is the slot cycle index. There are 16 * T slots in a slot cycle.

Example

If the slot cycle is 16 slots and the paging slot, calculated by using the IMSI, is 6, then the mobile monitors slots 6, 22, 38, 54, 60, 76, …

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6.3 Forward Link Coding - Overview

Walsh Code Assignment

PilotChannel

PageChannels

SyncChannel

TrafficChannels

PNI

PNQ

Iin

Qin

To RF modulation

BasebandFilterand

QuadratureMixer

The figure shows an overview of the IS-95 forward physical link structure for base station transmission. Some components will be discussed in more detail in this lesson.

Once the channels have been generated using their specific signal processing, the following steps are taken:

1. Appropriate Walsh codes are assigned to the channels in the Walsh code assignment.

2. The channels are then transmitted on both I- and Q-phases and multiplied by the I and Q PN sequences, respectively.

3. Finally, the I and Q channels are shaped and converted to the appropriate RF frequencies by the baseband filter and quadrature mixer.

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W

Forward Traffic Channel

Add FrameQuality

Indicator

Add 8 EncoderTail Bits

ConvolutionalEncoder

SymbolRepetition

BlockInterleaver

SymbolPuncture

ModulationSymbol

ChannelBits

Bits/Frame164080

172

2155

125267

Bits008

12

68

1012

Data Rate(kbps)

1.22.44.89.6

1.83.67.2

14.4

R1/21/21/21/2

1/21/21/21/2

Factor8x4x2x1x

8x4x2x1x

DeletionNoneNoneNoneNone

2 of 62 of 62 of 62 of 6

Symbols384384384384

384384384384

Rate (ksps)19.219.219.219.2

19.219.219.219.2

RS1

RS2

The channel bits (voice, data, or signaling) going into processing will first have a frame quality indicator attached so that the receiver can detect a bad frame. Next, tail bits are added to clear the encoder before the next frame enters the encoder.

The encoder adds forward error correction bits to the bit stream. On the forward link, the encoder is a convolutional encoder with coding coefficient, R = 1/2, and constraint length, K = 9.

The symbols coming out from the encoder is then repeated and punctured to achieve the appropriate symbol rate for the block interleaver. The block interleaver will interleave the bit stream for more robust transmission.

IS-95 was originally designed to support only Rate Set 1 (RS1); therefore, no symbol puncture is needed for RS1. RS2 was adder later to support the 13k vocoder. In order to support RS2 without significant changes in signal processing, two our of six symbols are punctured (deleted) before entering the block interleaver. This puncturing makes the effective coding coefficient, R= 3/4, for the RS2 encoder.

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X

W

Forward Link Scrambling and Power Control

Signal Point Mapping0 → +11→ -1

PowerControlSymbol

Puncture

ChannelGain

ModulationSymbol Rate

Forward PowerControl

Sub-ChannelGain

Power Control Bits± 1 Values

16 Bits per 20 ms Frame(800 bps)

PowerControl

Bit PositionExtractor

Long CodeGenerator

(1.2288Mcps)

Long CodeMask for User m


Puncture TimingControl (800 Hz)

Decimation Decimator

When the information signal has been interleaved, the modulation symbols will undergo scrambling. Scrambling is performed using a user-specific long code mask together with the long code. The user-specific long code is decimated before scrambling so that the correct symbol rate is achieved. The digital signal is then mapped as: ‘0’ to ‘+1’, ‘1’ to ‘-1’, and channel specific gain is applied. Next, power control bits (symbols) are inserted into the bit stream by puncturing and replacing existing bits.

The power control bits (PCB) make up the Power Control Sub-Channel. A power control algorithm determines the values of the PCBs. The information bits the PCBs are replacing are determined by the power control bit position extractor, which will pseudo-randomly puncture the symbols at a rate of 800 Hz.

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Power Control Sub-Channel

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

20 ms = 16 PCGs

ReverseTraffic Channel

16 17 18 19 20 21 22 23

1.25 ms = 24 modulation symbols

1 1 0 1

c0 c1 c2 c3

ForwardTraffic Channel

……

Scrambling bits

2 PCGs later

A Power Control Sub-Channel is continuously transmitted on the Forward Traffic Channel at a rate of one Power Control Bit (PCB) every 1.25 ms (800 bps). The bit indicates to the mobile station to increase (bit = ‘0’) or decrease (bit = ‘1’) its mean output power level. Based on the estimated received signal strength of the particular mobile station’s Reverse Traffic Channel over a 1.25 ms period (equivalent to six modulation symbols), a power control algorithm determines the value of the PCB.

The PCB is transmitted in the second power control group (PCG) following the corresponding Reverse Traffic Channel PCG in which the signal strength was estimated. The length of one PCB is exactly two modulation symbols of the Forward Traffic Channel and replaces two consecutive Forward Traffic Channel modulation symbols. This is called symbol puncturing. The PCB is pseudo-randomly inserted into the data stream after the data scrambling is performed.

Randomization of PCB Position

In every PCG, there are 24 bits, or modulation symbols, from the long code that are used for scrambling. The modulation symbols are numbered 0 through 23. The first 16 modulation symbols can used as possible starting positions for the PCB.

Scrambling bits 20 through 23 from the previous PCG are used to determine the starting position of the PCB. In the figure, these bits are identified as c0 through c3, respectively. The starting position of the PCB is determined as:

c0 + 2*c1 + 4*c2 + 8*c3

In the example shown, the values of bits 23, 22, 21, and 20 are ‘1011’ (11 decimal), and the power control bit starting position is the eleventh modulation symbol.

Impact of Gated Transmission

When the mobile station is using gated transmission on the reverse link, the mobile ignores the PCBs related to the gated-off periods.

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ModulationSymbol

19.2 ksps

Sync ChannelBits

32 Bits per26.666…ms FrameData Rate 1.2 kbps

Pilot, Paging, and Sync Channel

PilotChannels(All 0’s)

Signal PointMapping0 → +11→ -1

ChannelGain


ChannelGain

BlockInterleaver

(128 Symbols)

SymbolRepetition(2x Factor)

Conv.EncoderR = 1/2,

K = 9

ModulationSymbol

4.8 ksps


ChannelGain

BlockInterleaver

(384 Symbols)

SymbolRepetition


K = 9

PagingChannelBits

Decimator

Long CodeGenerator(1.2288 Mcps)

Long CodeMask forPaging

Channel p

19.2 kspsBits/20 ms96192

Data Rate (kbps)4.89.6

X

X

X

The graphic shows the structures of the Pilot Channel, Sync Channel, and Paging Channels.

The Pilot Channel spreads the all 0’s sequence with Walsh code 0. The channel is continuously broadcast throughout the cell in order to provide timing and phase information. The Pilot Channel is shared between all mobiles in the cell and is used to obtain acquisition of new multipath components and channel estimation (i.e., phase and multipath strength).

The Sync Channel is used by mobile stations operating within the coverage area of the base station to acquire initial time synchronization. Convolutional encoding and bit interleaving is performed to generate a robust signal.

A system may have multiple Paging Channels per carrier, up to seven Paging Channels. A Paging Channel can transmit at a data rate of 9.6 kbps or 4.8 kbps. In addition to convolutional encoding and bit interleaving, a long code mask specific to that particular Paging Channel is used to scramble the information, as well as to identify the particular channel.

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Final Steps in Forward Link Coding

RF

PN-Q-i(t)

cos ωct

PN-I-i(t)

LPFI

LPFQ

sin ωct+

Walsh code

x

After the channels have been generated, a specific Walsh code is assigned to each channel. The resulting bit stream is then transmitted on both the in-phase, I, and quadrature-phase, Q, components of the signal. This effectively makes the digital modulation BPSK. The I- and Q-phases are then quadrature-spread using the PN codes, PN-I-i(t) and PN-Q-i(t), respectively, with their appropriate time offset, i.

RF Modulation

After quadrature spreading, the signal is filtered, using a baseband filter, and then modulated in the frequency domain using a quadrature mixer. The modulated signal is amplified and sent to the antenna.

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6.4 Forward Link CDMA Codes

• Long code• Walsh code• Short code

– PN offset

– 512 available offsets.

For the forward link in IS-95, the CDMA codes, long code, short code, and Walsh code, are used as discussed in the CDMA Codes lesson. The short code is used to provide identification of an antenna face by using one of 512 time-offset of the code (PN offset). Long code and Walsh codes will be discussed further.

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Forward Link Long Code Masks

1100011001101 00000 PCN 000000000000 PILOT_PN

41 … 29 28 … 24 8 … 020 … 923 … 21

PagingChannel

01 40 LSBs of VPM

41 40 39 0…

1100011000 Permuted ESN

41 … 32 31 0…

TrafficChannel

For certain channels, the long code is used to scramble and give and identity to the channel. Data scrambling is accomplished by performing modulo-2 addition of the interleaver output symbol with binary value of the long code PN chip that is valid at the start of the transmission period of that symbol. The output of the long code mask is combined with output of the long code generator to obtain the scrambling sequence.

Shown are the long code masks used for the forward link channels in IS-95.

User Specific Long Code Mask

The long code mask for the Traffic Channel is user-specific and based on the ESN of the mobile. For the user specific long code mask a permuted version of the ESN is used.

For example, if the ESN of the mobile has 32 bits:

x31 x30 x29 x28 … x1 x0

Then the permuted ESN used for the long code mask would look like:

x0 x31 x22 x13 … x18 x9

Private Long Code Mask

For the user-specific long code mask, it is also possible to have a private mask based on encryption. The private mask is based on the 40 least significant bits (LSB) of the Voice Privacy Mask (VPM) as generated by a key generation procedure*.

* See Common Cryptographic Algorithms, Revision C, 1997. This is an EAR-controlled document subject to restricted distribution.

Long Code Generator

Long CodeMask

ScramblingSequence

PCN Paging Channel numberPILOT_PN F-PICH PN offsetPCN Paging Channel numberPILOT_PN F-PICH PN offset

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Forward Link Walsh Codes

• Reserved Walsh codes– F-PICH

• W064

– F-SYNC• W32

64

– F-PCH• W1

64 through W764

• Walsh codes not used can be used for Traffic Channels.

On the forward link in IS-95, the length of the Walsh code used is 64 bits, W64. Certain Walsh codes are reserved for the overhead channels, Pilot, Paging, and Sync Channels.

•The Pilot Channel is assigned W064. This Walsh code is unique in that it consists of only zeroes,

basically a DC (direct current) signal. All other Walsh codes used consists of an equal number of ones and zeroes.

•The Sync Channel is assigned W3264. W32

64 consists of 32 consecutive zeroes followed by 32 consecutive ones.

•The Paging Channels, up to seven channels, are assigned W164 through W7

64. W164 is assigned

the primary Paging Channel.

Any of the Walsh codes that are not used by a Paging Channel or the Sync Channel can be used by a Fundamental or Supplemental Code Channel.

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Outline - 3/4





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6.5 Reverse Link Channels - Overview

Traffic Channels

FundamentalCode

Channel

SupplementalCode

Channels

Access Channels

Reverse LinkChannel

The CDMA channel on the reverse link consists of:

•Fundamental Code Channel (R-FCH) - Carries speech, low speed data, signaling messages, and control information. For IS-95A, the Fundamental Code Channel is the Traffic Channel. For IS-95B, the Fundamental Code Channel is the Traffic Channel when no Supplemental Code Channels are used.

•Supplemental Code Channel (R-SCCH) - Up to seven SCCHs are used in IS-95B to increase the data rate for a reverse Traffic Channel.

•Access Channel (R-ACH) - Used when the mobile must access the system to initiate communication, or to respond to a direct message sent from the base station.

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Access Channel

• Access probes transmitted– Following the Access Protocol.

Access transmission length

AccessSlot N

AccessSlot N+1

AccessSlot N+2

20 ms Access Frame

SystemTime

Preamble Message Capsule

Sequence

The Access Channel is used when the mobile station must access the system to initiate communication or respond to a direct message sent from the base station. The mobile transmits access probes on the Access Channel using the access protocol, or procedure, discussed in the CDMA Concepts lesson. An access probe consists of a preamble and a message capsule, both of which are of a length of some number of frames (20 ms), determined by the system operator.

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6.6 Reverse Link Coding - Overview

Data Burst Randomizer

andLong Code Scrambling

TrafficChannel

PNI

PNQ

Iin

Qin

To RF modulation

BasebandFilterand

QuadratureMixerD

The figure shows an overview of the IS-95 reverse physical link structure for mobile station transmission. Some components will be discussed in more detail in this lesson.

Once the Traffic Channel has been generated using specific signal processing, the following steps are taken:

1. Data burst randomization and long code scrambling is performed to accommodate sub-rate frames, as well as scramble and identify the channel from the mobile.

2. The channel is then transmitted on both I- and Q-phases and multiplied by the I and Q PN sequences, respectively.

3. Finally, the I and Q channels are shaped and converted to the appropriate RF frequencies by the baseband filter and quadrature mixer.

Note: When the Access Channel is transmitted, similar processing is taking place. There is no data burst randomization for the Access Channel.

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RS1

RS2

Reverse Traffic Channel

Bits/Frame164080

172

2155

125267

Bits00812

681012

Data Rate(kbps)

1.22.44.89.6

1.83.67.2

14.4

R1/31/31/31/3

1/21/21/21/2

Factor8x4x2x1x

8x4x2x1x

Symbols576576576576

576576576576

Rate (ksps)28.828.828.828.8

28.828.828.828.8

W

Add FrameQuality

Indicator



SymbolRepetition

BlockInterleaver

64-aryOrthogonalModulator

ModulationSymbol

ChannelBits

Rate (kcps)307.2307.2307.2307.2

307.2307.2307.2307.2

The channel bits (voice, data, or signaling) going into processing will first have a frame quality indicator attached so that the receiver can detect a bad frame. Next, tail bits are added to clear the encoder before the next frame enters the encoder.

The encoder adds forward error correction bits to the bit stream. Similar to the forward link, convolutional coding is used with a constraint length of K=9. The coding coefficient, R, depends on the Rate Set to be transmitted. See the figure.

The symbols coming out from the encoder are then repeated to achieve the appropriate symbol rate for the block interleaver. The block interleaver will interleave the bit stream for more robust transmission.

After the block interleaver, 64-ary orthogonal modulation is performed. 64-ary orthogonal modulation, or just 64-ary modulation, can be seen as a type of digital modulation that makes the information stream more robust. With 64-ary modulation, a group of six bits from the block interleaver is changed (modulated) into 64 bits, a Walsh code (W64). After the 64-ary modulation the chip rate is 307.2 kcps. Further spreading is done in the scrambling process.

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Access Channel

Bits/Frame88

Data Rate(kbps)

4.8R

1/3Factor

2xSymbols

576Rate (ksps)

28.8

WAdd 8

EncoderTail Bits


SymbolRepetition

BlockInterleaver

64-aryOrthogonalModulator

ModulationSymbol

ChannelBits

Rate (kcps)307.2

The coding of the Access Channel is similar to the coding of the Reverse Traffic Channel with a data rate of 4.8 kbps. There is no frame quality indicator needed for the Access Channel; instead, tail bits are added immediately to clear the encoder before the next frame enters the encoder.

The encoder adds forward error correction bits to the bit stream. Convolutional coding is used with a constraint length of K=9 and a coding coefficient of R=1/3.

The symbols coming out from the encoder are then repeated to achieve the appropriate symbol rate for the block interleaver. The block interleaver will interleave the bit stream for more robust transmission.

Similar to the Reverse Traffic Channel, 64-ary orthogonal modulation is performed after the block interleaver. After the 64-ary modulation, the chip rate is 307.2 kcps. Further spreading is done in the scrambling process.

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64-ary Orthogonal Modulator

• Six bits converted to a Walsh code– Spreading more than 10 times

– Accounts for about 10 dB of processing gain

• Receiver can easily detect Walsh codes.

… 1 0 1 1 1 0 0 1 0 1 1 0 …

… 0011110000111100110000111100001100111100001111001100001111000011 …

W2264

c5 c4 c3 c2 c1

On the reverse link in IS-95, 64-ary orthogonal modulation, or 64-ary modulation, is performed. With 64-ary modulation, one of 64 possible modulation symbols, Walsh codes, is transmitted for each six code symbols. The modulation symbol index is selected as follows:

index = c0 + 2*c1 + 4*c2 + 8*c3 + 16*c4 + 32*c5

where c5 represents the last (or most recent), and c0 the first (or oldest) binary value of each group of six code symbols (bits) that form the modulation symbol index. Given the index, the transmitted modulation symbol is Windex

64.

The transmission period for a single modulation symbol is 1/4800 second (= 208.333... µs). The period of time associated with one-sixty-fourth of the modulation symbol is referred to as a Walsh chip and is equal to 1/307200 second (= 3.255... µs).

The 64-ary modulation spreads the information more than 10 times (64 / 6), and accounts for about 10 dB of the final processing gain experienced in the system.

From the receivers point of view, receiving Walsh codes are beneficial. The orthogonal property of Walsh codes makes for easy detection at the receiver. Only a portion of the modulation symbol needs to be correctly received in order to determine the original bits.

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Final Steps in Reverse Link Coding

RF

PN-Q-i(t)

cos ωct

PN-I-i(t)

LPFI

LPFQ

sin ωct+

LCM

w

D

Data BurstRandomizer

LCG

LCG Long Code GeneratorLCM Long Code MaskLPF Low-Pass Filter

LCG Long Code GeneratorLCM Long Code MaskLPF Low-Pass Filter

When a Traffic Channel has been generated, it will undergo a data burst randomization process to gate the transmission. Gating of the transmission is needed to achieve the various sub-rates (1/2, 1/4, and 1/8 rate).

Note: The Access Channel is not undergoing the data burst randomization.

Both the Traffic Channel and Access Channel will be scrambled using a specific long code mask (LCM) and the long code generator (LCM). Obviously, the Traffic Channel and the Access Channel are not transmitting at the same time.

The resulting bit stream is then transmitted on both the in-phase, I, and quadrature-phase, Q, component of the signal. The I- and Q-phases are then quadrature spread using the PN codes, PN-I-i(t) and PN-Q-i(t) respectively, with the zero time offset, i = 0.

In order to maximize the battery life for a mobile, the mobile’s amplifier has to be efficient. For the amplifier to be efficient, the peak-to-average (P/A) power ratio of the signal should be as small as possible.

Zero-crossings in the constellation (see Digital Modulation in the CDMA Codes lesson) increase the P/A power ratio of the signal. Signals with a high P/A ratio may saturate the amplifier, which in turn may cause out-of-band emission (interference outside the channel’s bandwidth). High P/A ratio also decreases the amplifier’s efficiency and therefore reduces battery life. The goal for modulation is to reduce the P/A ratio.

After quadrature spreading, a delay of 1/2 chip (406.9 ns) on the Q-phase, illustrated by the D-box, provides offset quadrature spreading to eliminate phase transitions of 180° from the reverse link since the I- and Q-phases never will change bit values at the same time. This type of modulation is also called Offset Quadrature Phase Shift Keying (OQPSK).

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Gated Transmission

• Gated transmission is used to achieve 1/2 rate, 1/4 rate, and 1/8 rate for a frame– Transmitter’s duty cycle depends on sub-rate

• A PCG is gated-on or gated-off– Gated-on PCGs are pseudo-random within a frame

– Data burst randomization algorithm controls what PCGs that are gated-on

• Ensures that every code symbol from encoder is transmitted exactly once.

• Output power reduced by at least 20 dB for gated-off PCG.

Prior to transmission, the Reverse Traffic Channel interleaver output stream is time gated to allow transmission of certain interleaver output symbols and deletion of others. The duty cycle of the transmission gate varies with the transmit data rate.

When the transmit data rate is at full rate (9.6 or 14.4 kbps), the transmission gate allows allinterleaver output symbols to be transmitted, which means a duty cycle of 100%. When the transmit data rate is 1/2 rate (4.6 or 7.2 kbps), the transmission gate allows one-half of theinterleaver output symbols to be transmitted (duty cycle of 50%). The duty cycles for 1/4 rate and 1/8 rate are then 25% and 12.5%, respectively.

The gating process operates on the power control groups (PCG). Certain PCGs are gated-on (i.e., transmitted), while other groups are gated-off (i.e., not transmitted). There are 16 PCGs in a frame.

The assignment of gated-on and gated-off PCGs is performed by the data burst randomization algorithm. The gated-on PCGs are pseudo-random in their positions within the frame. The data burst randomizer ensures that every code symbol input to the repetition process is transmitted exactly once.

During the gated-off periods, the mobile station reduces its output power by at least 20 dB, thus reducing the interference to other mobile stations operating on the same Reverse CDMA Channel.

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Data Burst Randomization Algorithm

Previous frame

20 ms = 16 PCGs

FullRate

0 0 1 0

b0 b1 b2 b3

…

Scrambling bits example

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1512 13 14 15

Previous frame

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1512 13 14 15

Previous frame

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1512 13 14 15

Previous frame

1/2Rate

1/4Rate

1/8Rate

b4 b5 b6 b7 b8 b9 b10 b11 b12 b13

1 1 0 1 1 0 0 1 …0 0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1512 13 14 15

PCG 14 PCG 15

The data burst randomizer generates a masking pattern of ‘0’s and ‘1’s that randomly masks out the redundant data generated by the code repetition. The masking pattern is determined by the data rate of the frame and by a block of 14 bits taken from the long code. These 14 bits are the last 14 bits of the long code used for spreading in the previous to the last power control group of the previous frame. See the figure. The bits are denoted as

b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13

where b0 represents the oldest bit, and b13 represents the latest bit. The PCGs gated-on are then determined based on the rate of the transmitted frame.

The figure shows transmitted PCGs if b0 through b13 were

0 0 1 0 1 1 0 1 1 0 0 1 0 0

Full Rate Frame

Transmit all 16 PCGs.

1/2 Rate Frame

Transmit the following eight PCGs:

b0, 2+b1, 4+b2, 6+b3,8+b4, 10+b5, 12+b6, 14+b7

1/4 Rate Frame

Transmit the four PCGs shown in the table to the right.The PCGs transmitted depends on the state of several bits.

1/8 Rate Frame

Transmit the two PCGs shown in the table below. ThePCGs transmitteddepends on the stateof several bits.

Transmission#(b8,b12) = (0,0) (b8,b12) = (1,0) (b9,b12) = (0,1) (b9,b12) = (1,1)

1 b0 2+b1 4+b2 6+b3

(b10,b13) = (0,0) (b10,b13) = (1,0) (b11,b13) = (0,1) (b11,b13) = (1,1)2 8+b4 10+b5 12+b6 14+b7

Transmit PCG#

Transmission#b8 = 0 b8 = 1

1 b0 2+b1

b9 = 0 b9 = 12 4+b2 6+b3

b10 = 0 b10 = 13 8+b4 10+b5

b11 = 0 b11 = 14 12+b6 14+b7

Transmit PCG#

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6.7 Reverse Link CDMA Codes

• Long Code• Walsh Code

– Used for 64-ary orthogonal modulation

• Short Code– Zero offset for quadrature spreading.

For the reverse link in IS-95, the CDMA codes, long code, short code, and Walsh code, are used as discussed in the CDMA Codes lesson. The Walsh codes were used to perform 64-arymodulation for a more robust reverse link. The short code is used to perform quadraturespreading with the zero-offset (PN offset 0) code sequence. The long code will be discussed further.

CL8300-SG.en.UL 178



Reverse Link Long Code Masks

110001111 ACN PCN BASE_ID PILOT_PN

41 … 33 32 … 28 8 … 024 … 927 … 25

AccessChannel

01 40 LSBs of VPM

41 40 39 0…


41 … 32 31 0…

TrafficChannel


Shown are the long code masks used for the reverse link channels in IS-95.

User-Specific Long Code Mask

The long code mask for the Traffic Channel is user-specific and based on the ESN of the mobile. For the user-specific long code mask, a permuted version of the ESN is used.



* See Common Cryptographic Algorithms, Revision C, 1997.This is an EAR-controlled document subject to restricted distribution.

Long Code Generator

Long CodeMask

ScramblingSequence

ACN Access Channel numberPCN Paging Channel numberBASE_ID Base station identifierPILOT_PN F-PICH PN offset

ACN Access Channel numberPCN Paging Channel numberBASE_ID Base station identifierPILOT_PN F-PICH PN offset

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Summary Of Code-Sequences – IS-95

Quadrature set ofmodified PN short codes

PN-I-i(t) = PN-I-0 (t - i x64Tc)

PN-Q-i(t) = PN-Q-0 (t - i x64Tc)

42 bit mask identifies user

Walsh functions are used to identify channels

PN Long Codes

242 - 1 bits

Walsh Functions - Wi

Walsh functions are used for64-ary orthogonal modulation

215 bits

Used for scrambling

64 chip offsets used to identify antenna face to the mobile

64 bits

Zero offset code is used for spreading

Forward Link Reverse Link

PN Long Code

The long code gets its name from the fact that it takes about 41.4 days for the code to repeat itself. Information about the long code is broadcast to the mobile station by the Sync Channel to help the mobile lock onto the base station and helps provide separation from other base stations.

For the reverse link, the long code and the long code mask is used to identify the signal from a specific user.

PN Short Code

One of the codes used in conjunction with the Walsh Code is the PN (pseudo-random noise) short code. The PN short code on the forward link is used to provide the base station with a unique identification that the mobile station uses to identify the serving base station.

For the reverse link, the PN short code is with a zero offset (no offset) to perform quadrature spreading.

Walsh Functions

A channel is multiplied by a Walsh function, or Walsh code. The Walsh code provides each user or channel with a unique identifier and, in DS spreading, spreads the frame across the entire bandwidth.

One of the most important properties of the Walsh function is that different codes are orthogonal with each other.

On the reverse link in IS-95, the Walsh function is used to perform 64-ary orthogonal modulation. Six code symbols are changed into a 64 bit Walsh function.

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Outline - 4/4





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6.8 Primary and Signaling Traffic

• Multiplex Option specifies the type of frame used– Called MuxPDU in IS-2000

• Signaling is transmitted as blank-and-burst or dim-and-burst.

MM Mixed Mode bitTT Traffic Type bitTM Traffic Mode bits

MM Mixed Mode bitTT Traffic Type bitTM Traffic Mode bits

Multiplex Option 1

Transmit Rate

Primary Traffic

Signaling Traffic

[bps] MM TT TM [bits/frame] [bits/frame]0 - - 171 01 0 00 80 88

9600 1 0 01 40 1281 0 10 16 1521 0 11 0 168

4800 - - - 80 02400 - - - 40 01200 - - - 16 0

Format Bits

Transmit Rate

Primary Traffic

Signaling Traffic

[bps] MM TT TM [bits/frame] [bits/frame]0 - - 171 01 0 00 80 88

9600 1 0 01 40 1281 0 10 16 1521 0 11 0 168

4800 - - - 80 02400 - - - 40 01200 - - - 16 0

Format Bits

The Multiplex Option (MO) specifies how much and what type of information are transmitted in a frame. IS-95 has two MOs. MO1 supports frames for Rate Set (RS) 1, and MO2 supports frames for RS2. Shown in the table is MO1.

In IS-2000, the MO is called a MuxPDU (Multiplex Sub-layer Protocol Data Unit) of a certain type. MuxPDU Type 1 corresponds to MO1, and MuxPDU Type 2 corresponds to MO2. There are more MuxPDU types defined in IS-2000.

For a full rate MO1 frame (9.6 kbps), there are a total of 172 bits. These bits can be used for primary traffic, secondary traffic, and signaling traffic. The allocation of bits between these traffic types are determined, for the 9.6 kbps frame, by three format bits: Mixed Mode (MM) bit, Traffic Type (TT) bit, and Traffic Mode (TM) bits.

When the MM bit is set to ‘0’, only primary traffic is carried in the frame. There are 171 primary traffic bits and one MM bit. The TT bit and TM bits are not used when the MM bit is ‘0’. When the MM bit is set to ‘1’, signaling or secondary traffic can also be transmitted in the frame.

When transmitting mixed traffic types in a frame, the TT bit and TM bits must be specified. The TT type specifies if the traffic, in addition to the primary traffic, is signaling traffic (TT = ‘0’) or secondary traffic (TT = ‘1’). The TM bits then control the allocation of bits between primary traffic and signaling/secondary traffic. See table.

In a frame, the format bits are at the beginning of the frame, followed by the primary traffic bits (if any). The signaling and secondary bits are added last to the frame.

Blank-and-Burst vs. Dim-and-Burst

If the TM bits are ’11’, then the entire frame consists of signaling or secondary traffic. We say that the signaling/secondary traffic is transmitted as blank-and-burst; all primary traffic bits are removed.

If the TM bits are ’00’, ’01’, or ’10’, then just some of the frame consists of signaling or secondary traffic. In this case, we say that the signaling/secondary traffic is transmitted as dim-and-burst; some primary traffic bits are removed.

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Summary

• High speed data is implemented in IS-95B using Supplemental Code Channels

• Forward link– Overhead channels and Traffic Channels transmitted

simultaneously

– PCBs are sent to the mobile using puncturing– Modulation symbol transmitted on I- and Q-phase; BPSK

• Reverse link– Q-phase is offset 1/2 chip; OQPSK

– 64-ary modulation is used– Gated transmission based on data burst randomization algorithm

• Multiplex option, frame configuration, and data rate determines the number of traffic bits per frame.

The maximum data rate in IS-95A is 14.4 kbps (rate set 2). In IS-95B, high speed data is implemented using aggregated Supplemental Code Channels. With Supplemental Code Channels, the maximum data rate can be 115.2 kbps (rate set 2).

Forward Link

On the forward link in IS-95, the overhead channels (Pilot, Paging, and Sync Channels) aretransmitted at the same time as the Traffic Channels. Separation of the channels are done with the Walsh codes.

Power control bits (PCB) are transmitted by puncturing information bits. The puncturing is pseudo-random. The PCBs tell the mobile station to increase or decrease its transmit power.

On the forward link in IS-95, the same modulation symbol is transmitted on both the I-phase and Q-phase components of the RF signal. This scheme effectively makes the modulation BPSK.

Reverse Link

Prior to the quadrature spreading (RF), the reverse link signal undergoes 64-ary modulation. Six code symbols are transformed into a 64 bit modulation symbol (Walsh code).

On the reverse link in IS-95, the same modulation symbol is transmitted on both the I-phase and Q-phase components of the RF signal. However, a 1/2 chip delay is introduced to the Q-phase. This scheme effectively makes the modulation OQPSK.

In order to reduce interference and achieve the reverse link sub-rates for a frame, gated transmission is incorporated. When to gate the transmission on or off is pseudo-randomly determined by a data burst randomization algorithm.

Multiplex Option

The format of a frame transmitted in IS-95 is determined by a multiplex option. The number of traffic bits per frame is determined by the multiplex option, the frame configuration, and the data rate of the frame.

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Knowledge Check

1. From a Walsh code perspective, how many active users can be supported with a data rate of 115.2 kbps?A. 1

B. 4

C. 7D. 8

2. System performance is enhanced with revision B of IS-95 due to what improvement or improvements?A. Enhanced coding of the Traffic ChannelB. Implementation of the access handoff features

C. The 64-ary orthogonal modulator

D. All of the above

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3. Match the following signal processing steps with the order in which they are performed for a Traffic Channel:A. Encoder 1. Step 1

B. Block interleaver 2. Step 2

C. Frame quality indicator 3. Step 3D. Symbol repetition/puncturing 4. Step 4

4. What is the duty cycle during gated transmission of a 1/2 rate frame?A. 100%B. 50%

C. 25%

D. 12.5%

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5. How many bits are transmitted after the following bit stream has gone through the 64-ary orthogonal modulator?

0 1 1 0 1 1 1 0 0 1 0 1 0 0 1 0 0 1

A. 42B. 54

C. 162

D. 192

CL8300-SG.en.UL 186



A. 1, 7, 10, 15

B. 1, 7, 10, 13C. 3, 4, 11, 15

D. 3, 4, 10, 15


6. Given the scrambling bits in the previous frame as shown below, what power control groups (PCG) are transmitted for a 1/4 rate frame?

Previous frame

20 ms = 16 PCGs

1 0 0 1

b0 b1 b2 b3

…

Scrambling bits example

1/4Rate

b4 b5 b6 b7 b8 b9 b10 b11 b12 b13

1 0 1 1 0 1 1 1 …0 1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1512 13 14 15

PCG 14 PCG 15

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Lesson Objectives

• Explain how high speed data is implemented• Explain the signal processing steps for a Traffic Channel• Explain the benefits of complex scrambling• Describe the implementation of multi-carrier mode• Identify the use of the CDMA codes• Explain the role of reverse link Pilot Channel in power

control.

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Outline - 1/4




• Operation specifics– Reverse access

– Handoff

– Power control.

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• Backward compatibility with IS-95– Overlay with IS-95B on the same 1.23 MHz channel

– Reuse of same base stations and IS-41D infrastructure

– Handoff from IS-95 to IS-2000 and IS-2000 to IS-95

• Faster data rates and double voice traffic through technology enhancements– Enhanced convolutional coding and Turbo codes

– Reverse link pilot for coherent detection

– Faster forward power control at 800Hz

– Supplemental channels for high data rates

• Supporting intelligent antennas and transmit diversity.

The main design characteristics of IS-95 are:

•Overlay with AMPS (analog) systems

•Frequency reuse of N=1

•Soft handoff

•Variable rate vocoders

•Fast power control.

In addition to the IS-95 characteristics, IS-2000 provides:

•Backward compatibility with IS-95:

– Overlay with IS-95B on the same 1.23 MHz channel

– Reuse of same base stations and IS-41D core network infrastructure

– Handoff from IS-95 to IS-2000 and IS-2000 to IS-95

•Faster data rates and double voice traffic through technology enhancements

•Pilot channels on the reverse link for coherent detection at the base station, which enable mobiles to transmit at less power. The continuous pilot channel broadcast provides power control, timing, and phase independent of transmission rate and fast initial acquisition with a minimum of hardware complexity.

•Faster forward and reverse link power control at 800 times per second

•Intelligent Antennas, either switch beam or adaptive array beam, that steer a narrower beam lobe in the direction of the mobile user, and transmit diversity. These techniques are designed to increase capacity.

•Turbo coding at higher transmission rates (greater than 14.4 kbps) for improved error detection

•Supplemental channel for higher data rates.

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Spreading Rates

• IS-95 uses a single spreading rate of 1.2288 Mcps.• IS-2000 uses spreading rates (SR) from 1.2288 to

14.7456 Mcps:– 1X = SR1 = 1 x 1.2288 Mcps

– 3X = SR3 = 3 x 1.2288 Mcps

– 6X = SR6 = 6 x 1.2288 Mcps*– 9X = SR9 = 9 x 1.2288 Mcps*

– 12X = SR12 = 12 x 1.2288 Mcps*

* Not supported by current TIA/EIA IS-2000 standards

In IS-95, the spreading rate (SR) is 1.2288 Mcps. IS-2000 builds on IS-95 and provides an evolutionary process to achieve data rates of up to 2 Mbps in accordance with ITU’s specifications. The IS-2000 specifications were intended to use spreading rates from 1.2288Mcps to 14.7456 Mcps in order to provide data rate services ranging from 144 kbps to 2 Mbps. In the current versions of the standard specifications, spreading rates of 1.2288 Mcps (SR1) and 3.6864 Mcps (SR3) are defined. Higher spreading rates than SR3 may not be implemented as there are other technologies, such as the IS-856 standard, that more efficiently provide the higher data rates.

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IS-2000 Family Of Standards

• IS-2000-1• Introduction to CDMA2000 standards for spread spectrum systems

• IS-2000-2• Physical layer standard for CDMA2000 spread spectrum systems

• IS-2000-3• Medium Access Control (MAC) standard for CDMA2000 spread

spectrum systems

• IS-2000-4• Signaling Link Access Control (LAC) standard for CDMA2000 spread

spectrum systems

• IS-2000-5• Upper Layer (Layer 3) signaling standard for CDMA2000 spread

spectrum systems

• IS-2000-6• Analog signaling standard for CDMA2000 spread spectrum systems.

Unlike IS-95B, IS-2000 is structured in accordance with the International StandardOrganization’s (ISO) Open Systems Interconnection (OSI) model, and is defined in a family of standards. The IS-2000 family of standards specifies a spread spectrum radio interface using CDMA technology to meet the requirements for 3G wireless communication. These standards are:

•IS-2000-1: Introduction to CDMA2000 standards for spread spectrum systems

•IS-2000-2: Physical layer standard for CDMA2000 spread spectrum systems

•IS-2000-3: Medium Access Control (MAC) standard for CDMA2000 spread spectrum systems

•IS-2000-4: Signaling Link Access Control (LAC) standard for CDMA2000 spread spectrum systems

•IS-2000-5: Upper Layer (Layer 3) signaling standard for CDMA2000 spread spectrum systems

•IS-2000-6: Analog signaling standard for CDMA2000 spread spectrum systems.

The first standard, IS-2000-1, provides an introduction, describes CDMA2000 compatibility and the relationship with TIA/EIA-95B, lists related standards, and defines common aspects and naming conventions.

The next four standards, IS-2000-2 through IS-2000-5, specify CDMA2000 functional interface on Layers 1, 2, and 3, in accordance with the OSI reference mode. Layer 2, which is subdivided into the Link Access Control (LAC) sublayer and the Medium Access Control (MAC) sublayer, is described in IS-2000-3 and IS-2000-4. The last standard, IS-2000-6, specifies analog operation to support dual-mode mobiles and base stations.

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IS-2000 Layering Structure

– New for IS-2000

Multiplexing QoS Control

Best Effort Delivery RLPMACControlState

High-speed

Circuit Network

layer services

LAC Protocol Null LAC

MAC

LAC

Physical Layer

IPPPP

TCP UDPSignalingServices

Packet Data Application

VoiceServices

Circuit DataApplication

Physical Layer(OSI 1)

Link Layer(OSI 2)

Upper Layers(OSI 3-7)

IP: Internet ProtocolLAC: Link Access ControlMAC: Medium Access ControlOSI: Open System InterconnectPPP: Point-to-Point ProtocolQoS: Quality of ServiceRLP: Radio Link ProtocolTCP: Transmission Control ProtocolUDP: User Data Protocol

The major significance of the layering structure from the RF engineering perspective is found in the physical and link layers.

Upper Layer

The Upper Layer corresponds to the Application and Transport Layer Sets protocols assigned to Layers 3 through 7 in the OSI model. The Upper Layer supports multiple concurrent active sessions with any combination of service, and supports four basic services:

- Voice service- End user data bearing services- Signaling services (control all operational aspects of the mobile)- Multi-media services.

Link Layer

The Link Layer, is divides into the Medium Access Control (MAC) sublayer and a Link Access Control (LAC) sublayer. The MAC Protocol manages RF resources to keep total interference below acceptable level, whereas the LAC Protocol supports and controls mechanisms for data transport services.

MAC Sublayer

From the RF engineering point of view, in 3G, the MAC sublayer has major significance with respect to managing RF resources and insuring Quality of Service (QoS). The QoS allows users willing to pay more for services to subscribe to different classes of service.

To insure reliability, the MAC sublayer includes a Radio Link Protocol that attempts Best Effort Delivery by re-transmission of error data frames.

Physical Layer

The physical layer provides coding and modulation services for a set of logical channels used by the Link Layer, and generates a set of physical channels that are directly transmitted over the air interface.

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IS-2000 High Speed Data

IS-2000

IS-95

BaseStation F

S1

S2

1.25 MHz channel

Diversity Receiver

• Supplemental Channel (SCH) carries high speed data.– Requires Fundamental Channel (FCH) or Dedicated Control

Channel (DCCH) to carry signaling

• Each user can transmit and receive up to two SCH.• SCH can be shared or dedicated.

Traffic Channel

Pilot

High speed data in an IS-2000 system is achieved by utilizing Supplemental Channels.

Supplemental Channels

The number of Supplemental Channels (SCH) permitted to be transmitted by the base station is optional. In this regard, a service may configure the system in many ways.

•No SCH - A service provider may choose not to have any SCHs and not provide any high speed data capabilities. In this case, only voice and low speed data services are provided.

•Dedicated SCH - One or more (multiple) SCHs is available. If the SCHs are being used and another user requires high data rate service, the call is blocked until a SCH is available.

•Shared SCH - More than one user is assigned to a single or multiple SCHs. A user on the shared channel must share the channel resources with other users. The more users are assigned to the channel, the longer the latency experienced by each user. Each user must receive control data on either a separate Dedicated Control Channel (DCCH) or Fundamental Channel (FCH).

Sharing RF Resource

There two ways of sharing the RF resource:

•Assign each user its own SCH (dedicated SCH)

•Assign users to share one or more SCHs (shared SCH).

The service provider may use either or both methods within the system. If a separate SCH is assigned to a user, the transmission can be in a circuit switched mode. However, if users are assigned to share a SCH, the users must be in packet switched mode. Regardless of the method used, the fundamental objective is to keep the overall interference level below a maximum allowable total interference level. This interference management is handled through the MAC protocol that will schedule when and how long a user can transmit. The MAC protocol is transmitted to each user over either DCCH or FCH.

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High Speed Packet Data – Signaling and User Data

UserA

UserB

UserCA

B

C C

BA A

No SCH Dedicated SCH Shared SCHVoice/LSPD/LSCD HSPD/HSCD HSPD

1 user per SCH Multiple users,multiple SCH

No SCH Dedicated SCH Shared SCHVoice/LSPD/LSCD HSPD/HSCD HSPD

1 user per SCH Multiple users,multiple SCH

Control channelLSPD Low Speed Packet DataLSCD Low Speed Circuit DataHSPD High Speed Packet DataHSCD High Speed Circuit Data

Shared Supplemental Channel

A shared Supplemental Channel (SCH) is illustrated in the figure. In this illustration, each user is in communication with the base station on two channels. This means that each user is assigned two Walsh codes: One for user data on the shared SCH, and the other for control data, which can be over either a Fundamental Channel (FCH) or a Dedicated Control Channel (DCCH). More than one SCH may be needed to serve all the users.

Request and Scheduling of Transmission

For the reverse link, any request for user data is transmitted to the base station over the control channel. The base station will schedule transmission of the requested data over the shared SCH so that user data is sent from only one user at a time. If the base receives requests for user data from more than one user at the same time, the base station will make the decision about which user will be served first, based on user QoS or some other parameter. The transmission of user data is also scheduled to keep the total level of interference below the total allowable interference level.

For the forward link, the request does not have to be sent to the mobiles because the base station schedules the transmission. Instead, it is the RLP (Radio Link Protocol) that requests the transmission.

Dedicated Supplemental Channels

As with the shared SCH, when using a dedicated SCH, each user is in communication with the base station on two channels. This means that each user is assigned two Walsh codes: One for user data on its own dedicated SCH, and one for control on its own control channel, FCH or DCCH.

As described for the shared SCH, any request for user data is transmitted to the base station over the control channel. Even though each user has its own dedicated SCH, the mobile can only transmit over the reverse link when permitted by the MAC protocol that communicates to the mobile over the forward control channel. In this manner, the MAC protocol can schedule traffic on all reverse link SCH so as not exceeded the total allowable interference.

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Accumulative Interference

Maximum Allowable Total Interference Level

The total level of interference on the reverse RF channel is kept below the total allowable interference level by the MAC protocol control data that is transmitted to each user on its control channel. The MAC protocol will tell each user mobile when to transmit, the transmission data rate, and the duration.

Managing RF Resources

In IS-95, where most users sends voice data, management of the RF resource is relatively simple. The base station is able to handle a certain number of calls, after which additional calls are blocked. The number of calls is related to the Total Allowable Interference level.

In IS-2000, where a multitude of services are offered, each having a different data rate, the level of interference contributed from each user may differ considerably, making management of the Total Allowable Interference level more complex. This management is handled by the MAC protocol.

An example of this accumulated interference and the management scheme is shown in the figure. The amount of interference introduced by each user is a function of its transmitted data rate. Whenever a user accesses the network to transmit a message, it negotiates a level of service in accordance with its QoS. The amount of transmission time the MAC protocol allocates for each user is based on the user’s QoS and the current interference environment.

In the figure, five users are illustrated. User 1 may be using a voice application. Voice applications tend to have low data rates but the channel is used for a longer period of time. User 2 may be using a packet data application. Packet data is bursty by nature, which means that relatively high data rate bursts are transmitted during short time periods.

The MAC protocol will stack only those users who keep the total interference below the Minimum Allowable Total Interference level.

Please note that in the figure, interference levels and time durations are not shown in scale.

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Burst Control Function

• Schedules transmission to:– Maximize peak and average throughput per user and for the

entire system

– Minimize delay for each user

– Maximize the forward link power efficiency for entire system– Maximize the reverse link capacity utilization

– Trade-off fairness, priority, and capacity

• Determines, for each transmission, what user is to transmit, the SCH rate, and the burst duration

• May terminate bursts prematurely if loading approaches power or interference overload levels

• Not standardized, vendor-specific implementation– Lucent: Supplemental Air-Resource Allocation (SARA).

Since data in general is bursty by nature, especially packet data, there must be a function that can control the bursts to and from a number of users. IS-2000 specifies that the Medium Access Control (MAC) layer performs that functionality. However, IS-2000 does not specify how the burst control function within the MAC should operate; this is left up to the vendor to implement. The burst control functionality in a Lucent Technologies system is mostly handled by an algorithm called Supplemental Air-Resource Allocation, or SARA.

The burst control function tries to balance the individual QoS per user with the overall performance objectives for the entire system. Not only will the function determine who can transmit when with what rate and for how long, but the function can also terminate a burst prematurely to conserve precious resources. The resources could also be re-allocated to higher priority users or data.

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Data Call With Supplemental Channel

Data Rate[kbps]

1.2 kbps(FCH)

9.6 kbps(FCH)

19.2 kbps(SCH)

38.4 kbps(SCH)

76.8 kbps(SCH)

153.6 kbps(SCH)

DormantPeriod

Call #1 Call #N

User sessionLog on Log off

Data Call with Supplemental Channel

A data call does not need the high data bandwidth all the time, so the resources must be efficiently managed to maximize capacity. The figure shows the structure of a data call using the Supplemental Channel (SCH). The user session starts when a data user “logs on” to the system. During a session, several data calls may be made. Being “logged on” to the system does not necessarily mean that air-interface resources are allocated to the user. The time period where the user is still “logged on” but no resources are allocated to a call is called the dormant period.

Typically, the resources are released after some time of inactivity on the control channel. The time is controlled by the so called inactivity timer, or dormancy timer.

A data call needs a channel on which to transmit and receive signaling messages; the SCH is only used to transmit user data. For messaging, a Fundamental Channel (FCH) or a Dedicated Control Channel (DCCH) can be used. The figure shows a FCH for messaging. The SCH can only be set up once a FCH/DCCH is established.

If a data burst must be transmitted, the system will set up a SCH in addition to the FCH/DCCH to transmit the high speed data. The bandwidth of the SCH and the duration of the burst may be determined in order to maximize capacity and minimize interference.

In conclusion, with packet data applications, the user perceives that there is a constant connection to the IP network, “always on.” In reality, resources are only allocated when they are needed to transmission of data.

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Outline - 2/4





– Handoff

– Power control.

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Forward CDMA Channelfor SR1 and SR3

PilotChannels

SyncChannel

PagingChannels

(SR1)

CommonControl

Channels

TrafficChannels

0-1 FundamentalChannel

Mobile StationPower ControlSubchannel

0-7 SupplementalCode Channels Radio

Configurations 1-2

0-2 SupplementalChannels Radio

Configurations 3-9

QuickPaging

Channels

CommonPower Control

Channels

CommonAssignment

Channels

ForwardPilot

Channel

TransmitDiversity Pilot

Channel

AuxiliaryPilot

Channels

Auxiliary TransmitDiversity Pilot

Channels

0-1 DedicatedControlChannel

BroadcastControl

Channels

IS-95 Compatible Forward Link Channels

To maintain compatibility with IS-95, IS-2000 uses the same forward link channel functionalities that are used in IS-95. These channels are:

•Pilot Channel (F-PICH)* - Similar to the forward Pilot Channel in IS-95, it is used at the mobile to provide continuous time and phase reference. Each base station transmits the short PN code using Walsh code W0 (all zeros) over the F-PICH with a unique base station timing offset.

•Sync Channel (F-SYNC)* - In addition to providing system timing and network identification, the sync channel identifies the state of the long PN code so that the generation of the long PN code in the mobile is synchronized with the generation of the long PN code at the base station.

•Paging Channel (F-PCH)* - Provides notification of incoming calls to idle mobiles. In addition, the F-PCH may be used to broadcast messages.

•Fundamental Channel (F-FCH)* - For low data rates and voice calls that operate in the same way as IS-95 Traffic Channels for backwards capability. The FCH carries both message and control data.

•Supplemental Code Channel (F-SCCH) – Up to seven channels are used in IS-95B to increase the data rate for a Forward Traffic Channel.

Additional channels are specified in IS-2000. These channels will be discussed on the following pages.

* The channel is required in a IS-2000 system using spreading rate 1 to support typical voice operation.

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Forward Link Common Physical Channel (F-CPHCH)

F-PICH (Forward Pilot Channel)

F-PCH (Forward Paging Channel)F-QPCH (Quick Paging Channel)F-SYNC (Forward Sync Channel)F-CCCH (Forward Common Control Channel)F-BCCH (Forward Broadcast Control Channel)F-CPCCH (Forward Common Power Control Channel)F-CACH (Forward Common Assignment Channel)

F-CCHTForward Common Channel Type

F-CPHCH(Forward Common Physical Channel)

F-CAPICH (Forward Common Auxiliary Pilot Channel)

F-TDPICH (Transmit Diversity Pilot Channel)F-ATDPICH (Auxiliary Transmit Diversity Pilot Channel)

The Forward Link Common Physical Channel (F-CPHCH) is the collection of all physical channels that carry information from the base station to a set of mobiles in a point to multipoint manner. Multiple mobiles may receive the same F-CPHCH.

Two types of messages are carried on the F-CPHCH:

•Overhead messages (broadcast) in which multiple mobiles receive the message

•Directed messages to a single mobile, determined by use of an explicit mobile address.

The F-CPHCH is composed of:

•Forward Pilot Channel (F-PICH)Spreads the all 0’s sequence with Walsh code 0. The channel is continuously broadcast throughout the cell (sector) in order to provide timing, phase information, channel estimation, initial acquisition, power control, and handoffs.

•Forward Common Auxiliary Pilot Channel (F-CAPICH)Used with antenna beam-forming applications to generate spot beam. Spot beams can be used to increase coverage towards a particular geographical point or to increase capacity towards hot spots. The F-CAPICH can be shared among multiple mobiles in the same spot beam.

•Forward Transmit Diversity Pilot Channel (F-TDPICH)An unmodulated, direct-sequence spread spectrum signal transmitted continuously by a CDMA BS to support forward link transmit diversity. The F-PICH and F-TDPICH provide phase references for coherent demodulation of forward link CDMA channels which use transmit diversity.

•Forward Auxiliary Transmit Diversity Pilot Channel (F-ATDPICH)Associated with the Dedicated Auxiliary Pilot (F-DAPICH). Both F-DAPICH and F-ATDPICH provide phase reference for coherent demodulation of those forward links CDMA channels associated with the F-DAPICH and employ transmit diversity.

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Forward Link Common Physical Channel (F-CPHCH) – cont’d

F-PICH (Forward Pilot Channel)

F-PCH (Forward Paging Channel)F-QPCH (Quick Paging Channel)F-SYNC (Forward Sync Channel)F-CCCH (Forward Common Control Channel)F-BCCH (Forward Broadcast Control Channel)F-CPCCH (Forward Common Power Control Channel)F-CACH (Forward Common Assignment Channel)

F-CCHTForward Common Channel Type

F-CPHCH(Forward Common Physical Channel)

F-CAPICH (Forward Common Auxiliary Pilot Channel)

F-TDPICH (Transmit Diversity Pilot Channel)F-ATDPICH (Auxiliary Transmit Diversity Pilot Channel)

•Forward Common Channel Type (F-CCHT)

•Forward Paging Channel (F-PCH)Used to transmit system overhead information and mobile specific messages. Multiple F-PCHs can be configured per base station. Transmission data rate 9600 or 4800 bps.

•Forward Common Control Channel (F-CCCH)A common channel used for communication of Layer 3 and MAC messages to one or more mobiles. The F-CCCH can transmit longer messages and more data (frame sizes are 5 ms, 10 ms, and 20 ms) to individuals without setting up a dedicated channel. The coding parameters are identical to those of the F-PCH.

•Forward Sync Channel (F-SYNC)Used by mobile stations to acquire initial time synchronization and F-PCH location.

•Forward Broadcast Control Channel (F-BCCH)A paging channel dedicated to carry only the overhead messages and possible SMS broadcast message.

•Forward Common Power Control Channel (F-CPCCH)Used to transmit common power control subchannels (one bit per subchannel) for power control of multiple R-CCCH (Reverse Common Control Channel) and R-EACH (Reverse Enhanced Access Channel). The common power control subchannels are time multiplexed on F-CPCCH.

•Forward Quick Paging Channel (F-QPCH)Used to reduce the amount of time the mobile spends monitoring the paging channel resulting in extended battery life. The F-QPCH is using an uncoded and On-Off-Keying (OOK) modulated spread spectrum signal to inform mobiles operating in the slotted mode during the idle state whether to receive F-CCCH or F-PCH.

•Forward Common Assignment Channel (F-CACH)Used by the base station to acknowledge a mobile accessing the R-EACH, and in the case of reservation mode, to transmit the address of the R-CCCH and associated Common Power Control Sub-Channel (CPCSCH) on the F-CPCCH.

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F-SCCH0(Forward Supplemental Code Channel 0)

Forward Link Dedicated Physical Channel (F-DPHCH)

F-DPHCH(Forward Dedicated Physical Channel)

F-DAPICH(Forward Dedicated Auxiliary Pilot Channel)

F-DCCH(Forward Dedicated Control Channel)

F-FCH(Forward Fundamental Channel)

F-SCH1(Forward Supplemental Channel 1)

F-SCH2

F-SCCH7

F-SCHT

(Forward SupplementalChannel Type) ..

.

The Forward Link Dedicated Physical Channel (F-DPHCH) is the collection of all physical channels that carry information from the base station to a set of mobiles in a point to unipointmanner. Each mobile receives their own F-DPHCH.

The F-DPHCH is composed of:

•Forward Dedicated Auxiliary Pilot Channel (F-DAPICH)Used for beam steering and beam forming applications for a single mobile to increase the coverage or data rate towards that particular mobile.

•Forward Dedicated Control Channel (F-DCCH)Used to carry MAC and signaling information to a particular mobile. For transmitting control data to individual users on the SCH. The control data includes signaling for soft handoff, power control, and MAC protocol.

•Forward Fundamental Channel (F-FCH)Carries voice, data, and control information to a mobile user. The F-FCH is transmitted at variable rates and consequently requires rate detection at the mobile receiver.

•Forward Supplemental Channel Type (F-SCHT)

•Forward Supplementary Channel (F-SCH)Carries data to a mobile user. The F-SCH can be operated in two distinct modes. The first mode is used for data rates that do not exceed 14.4 kbps and uses blind rate detection (no scheduling or rate information provided). In the second mode, the rate information is explicitly provided by the base station (no blind rate detection is performed). There may be more than one F-SCH in use at a given time. The channel carries user data only and must be transmitted with either the FCH and/or DCCH.

•Forward Supplemental Code Channel (F-SCCH)Used to carry data to a mobile user. The F-SCCHs are used to provide backward compatibility for IS-95B.

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Forward Link Channel Types for the SR1 and SR3

SR3SR1

Forward Pilot Channel 1

Transmit Diversity Pilot Channel 1

Auxiliary Pilot Channel Not specified

Sync Channel 1

Broadcast Control Channel 8

Quick Paging Channel 3

Common Power Control Channel 4

Common Assignment Channel 7

Forward Common Control Channel 7

Forward Dedicated Control Channel 1*

Forward Fundamental Channel 1*

Forward Supplemental Channel (RC3-RC5) 2*

Auxiliary Transmit Diversity Pilot Channel Not specified

Forward Supplemental Coded Channel (RC1 and RC2)

7*

Paging Channel 7

1

N/A

Not specified

1

8

3

4

7

7

1*

1*

2*

N/A

N/A

N/A

Channel TypeMaximum Number

* Per forward traffic channel

The table shows the number of possible channels available per carrier in a SR1 and SR3 system. The number of traffic channels (each of which may consists of F-DCCH, F-FCH, F-SCH, and F-SCCH) is limited by availability of Walsh codes and other system resources.

Note that the F-PCH is not defined for SR3. The assumption is that the F-PCH will be replaced with other overhead channels, such as the F-BCCH and F-CACH.

Channel AcronymForward Pilot Channel F-PICHTransmit Diversity Pilot Channel F-TDPICHCommon Auxiliary Pilot Channel F-CAPICHDedicated Auxiliary Pilot Channel F-DAPICHAuxiliary Transmit Diversity Pilot Channel F-ATDPICHSync Channel F-SYNCBroadcast Control Channel F-BCCHPaging Channel F-PCHQuick Paging Channel F-QPCHCommon Power Control Channel F-CPCCHCommon Assignment Channel F-CACHForward Common Control Channel F-CCCHForward Dedicated Control Channel F-DCCHForward Fundamental Channel F-FCHForward Supplemental Channel F-SCHForward Supplemental Code Channel F-SCCH


CL8300-SG.en.UL 205



Forward Link Radio Configurations

RC SR Characteristics1 1 1200, 2400, 4800, and 9600 bps data rates with R=1/2, BPSK pre-

spreading symbols

2 1 1800, 3600, 7200, and 14400 bps data rates with R=1/2, BPSK pre-spreading symbols

3 1 1200, 1350, 1500, 2400, 2700, 4800, 9600, 19200, 38400, 76800, and 153600 bps with R=1/4, QPSK pre-spreading symbols, OTD allowed

4 1 1200, 1350, 1500, 2400, 2700, 4800, 9600, 19200, 38400, 76800, 153600, and 307200 bps with R=1/2, QPSK pre-spreading symbols, OTD allowed

5 1 1800, 3600, 7200, 14400, 28800, 57600, 115200, and 230400 bps with R=1/4, QPSK pre-spreading symbols, OTD allowed

6 3 1200, 1350, 1500, 2400, 2700, 4800, 9600, 19200, 38400, 76800, 153600, and 307200 bps with R=1/6, QPSK pre-spreading symbols, MC mode, OTD allowed

7 3 1200, 1350, 1500, 2400, 2700, 4800, 9600, 19200, 38400, 76800, 153600, 307200, and 614400 bps with R=1/3, QPSK pre-spreading symbols, MC mode, OTD allowed

8 3 1800, 3600, 7200, 14400, 28800, 57600, 115200, 230400, and 460800 bps with R=1/4 (20ms) or R=1/3 (5ms), QPSK pre-spreading symbols, MC mode, OTD allowed

9 3 1800, 3600, 7200, 14400, 28800, 57600, 115200, 230400, 460800, 1036800 bps with R=1/2 (20ms) or R=1/3 (5ms), QPSK pre-spreading symbols, MC mode, OTD allowed

The radio configuration (RC) determines the coding and modulation of the FCH and SCH.

For the forward link, there are six radio configurations (RC) defined: RC1 through RC9. RC1 and RC2 correspond to IS-95 Rate Set (RS) 1 and 2, respectively. The details regarding coding for RC1 and RC2 can be found in the IS-95 Specifics lesson. The first five RCs are for the 1X spreading rate (SR1), and the last four for the 3X spreading rate (SR3).

Note that there are two radio configurations for SR1 supporting N*9.6 kbps, RC3 and RC4. The difference between RC3 and RC4 is that RC3 has a coding coefficient of R=1/4 and supports up to 64 Walsh codes. RC4 has a coding coefficient of ½ and supports up to 128 Walsh codes. There are more radio configurations on the forward link than on the reverse link.

Note: For RCs 3, 4, 6, and 7, the lowest data rate (“1/8 rate”) for the F-FCH is 1500 bps. The data rates of 1200 bps and 1350 bps are for the F-SCH with frames of size 80 ms and 40 ms, respectively. The F-SCH with frames of size 40 ms and 80 ms also use the data rate of 2400 bps instead of 2700 bps.

CL8300-SG.en.UL 206




RotationFunction

De-multiplexingFunction

F-CCCHF-CACHF-CPCCF-QPCHF-BCCH

F-PCHF-PICH

F-CPICHF-SYNC

PNI PNQ

Long Code Scrambling,

Power Control, Signal Point

Mapping

LCG LCM

F-FCH F-SCH F-DCCH

CPICH Common Pilot ChannelsLCG Long Code GeneratorLCM Long Code MaskQOF Quasi-orthogonal Function

CPICH Common Pilot ChannelsLCG Long Code GeneratorLCM Long Code MaskQOF Quasi-orthogonal Function

Walsh Function

Iin

Qin

QOF Sign

To RF modulation

BasebandFilterand

QuadratureMixer

ComplexMultiplier

The figure shows an overview of the IS-2000 forward physical link structure for base station transmission. Some components will be discussed in more detail in this lesson.

Once the channels have been generated using their specific signal processing, the following steps are taken:

1. The de-multiplexing function combines a number of channels for transmission and forms an I and an Q stream for the forward link.

2. Several of the channels require spreading as provided by the long code generator (LCG) and long code mask (LCM).

3. The long code scrambling, power control, and signal point mapping function combines the output of the long code generator with the data stream of the appropriate channel, maps 0's and 1' to +1' and -1's, and punctures power control information.

4. The symbol repetition function duplicates symbols if necessary, and is dependent upon the transmission rate.

5. The output is multiplied, if enabled, by a quasi-orthogonal function (QOF) to provide almost (quasi) orthogonal separation.

6. When enabled, the rotation function rotates the I- and Q-phases (-Q is mapped to I and I is mapped to Q).

7. These outputs are then multiplied by the I- and Q-phase PN sequences, as provided by the complex multiplier function, or complex scrambling.

8. Finally, the I- and Q-phase channels are shaped and converted to the appropriate RF frequencies by the baseband filter and quadrature mixer.

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W

F-FCH and F-SCH - RC3

Add FrameQuality

Indicator

Add 8 Reserved/EncoderTail Bits

Convolutionalor TurboEncoder

SymbolRepetition

BlockInterleaver

SymbolPuncture

ModulationSymbol

ChannelBits

Bits/Frame24 Bits/5 ms

16 Bits/20 ms40 Bits/20n ms80 Bits/20n ms

172 Bits/20n ms

360 Bits/20n ms744 Bits/20n ms

1,512 Bits/20n ms3,048 Bits/20n ms

1 to 3,047 Bits/20n ms

Bits16

668

12

16161616

Data Rate(kbps)

9.6

1.52.7/n4.8/n9.6/n

19.2/n38.4/n76.8/n153.6/n

R1/4

1/41/41/41/4

1/41/41/41/4

Factor1x

8x4x2x1x

1x1x1x1x

DeletionNone

1 of 51 of 9NoneNone

NoneNoneNoneNone

Symbols192

768768768768

1,5363,0726,144

12,288

Rate (ksps)38.4

38.438.4/n38.4/n38.4/n

76.8/n153.6/n307.2/n614.4/n

Analogous to the Reverse Fundamental Channel (R-FCH), the Forward Fundamental Channel (F-FCH) is similar to that of the 2G traffic channel. The figure shows an example of the F-FCH and F-SCH processing for RC3. The data rate for RC3, as seen at the input of the encoder, can be up to 9.6 kbps for the FCH, and up to 153.6 kbps for the SCH.

The channel bits (voice, data, or signaling) going in to the processing will first have a frame quality indicator attached so that the receiver can detect a bad frame. Next, tail bits are added to clear the encoder before the next frame enters the encoder. The encoder adds forward error correction bits to the bit stream. Depending on application, convolutional or turbo encoding is used. The symbols coming out from the encoder are then repeated and punctured to achieve the appropriate symbol rate for the block interleaver. The block interleaver will interleave the bit stream for more robust transmission.

The table shows the available processing parameters for F-FCH and F-SCH for RC3. While the processing steps are the same, the processing parameters for other radio configurations (e.g., RC4) are different.

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X

W

Forward Link Scrambling and Power Control - SR1

Signal Point Mapping0 → +11→ -1

PowerControlSymbol

Puncture

ChannelGain


Forward PowerControl

Sub-ChannelGain

Power Control Bits± 1 Values

16 Bits per 20 ms Frameor 4 bits per 5 ms Frame

Decimator

PowerControl

Bit PositionExtractor

Long CodeGenerator

(1.2288Mcps)

Long CodeMask for User m


Puncture TimingControl (800 Hz)

Decimation

When the information signal has been interleaved, it will undergo scrambling. Scrambling is performed using a user-specific long code mask together with the long code. The digital signal is then mapped as: ‘0’ to ‘+1’, ‘1’ to ‘-1’. A channel specific gain is applied and power control commands (symbols) are inserted into the bitstream by puncturing (“replacing”) existing bits.

After the power control symbol puncturing, the data stream is added to other channels and undergoes further processing steps, such as quadrature spreading. Before we discuss those steps, we will take a look at the coding of some of the other channels transmitted on the forward link.

CL8300-SG.en.UL 209



ModulationSymbol

19.2 ksps

Sync ChannelBits

32 Bits per26.666…ms FrameData Rate 1.2 kbps

F-PICH, F-SYNCH and F-PCH - SR1

PilotChannels(All 0’s)


ChannelGain X1

XQ

XQ

0

0


ChannelGain

BlockInterleaver

(128 Symbols)

SymbolRepetition(2x Factor)


K = 9

ModulationSymbol

4.8 ksps

XQ0


ChannelGain

BlockInterleaver

(384 Symbols)

SymbolRepetition


K = 9

PagingChannelBits

Decimator

Long CodeGenerator(1.2288 Mcps)

Long CodeMask forPaging

Channel p

X1

X1

19.2 kspsBits/20 ms96192


The graphic shows the structures of the Forward Pilot Channel (F-PICH), Forward Sync Channel (F-SYNC), and Forward Paging Channels (F-PCH).

The Forward Pilot Channel (F-PICH) spreads the all 0’s sequence with Walsh code 0. The channel is continuously broadcast throughout the cell in order to provide timing and phase information. The F-PICH is shared between all mobiles in the cell and is used to obtain acquisition of new multipath components and channel estimation (i.e., phase and multipathstrength).

The Forward Sync Channel (F-SYNC) is used by mobile stations operating within the coverage area of the base station to acquire initial time synchronization. Convolutional encoding and bit interleaving is performed to generate a robust signal.

A system may have multiple Forward Paging Channels (F-PCH) per carrier. A F-PCH can transmit at a data rate of 9.6 kbps or 4.8 kbps. In addition to convolutional encoding and bit interleaving, a long code mask specific to that particular F-PCH is used to scramble the information on the F-PCH. The long code mask is also used to identify a particular F-PCH.

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ModulationSymbol

19.2 ksps

F-QPCH - SR1

• Works together with the F-PCH– Reduces amount of time MS spends in monitoring F-PCH

– Contains a single bit message.

SymbolRepetition(2x or 4x)

Signal Point Mapping+1 When Indicator Enabled

0 Otherwise

Quick Paging ChannelIndicators

Indicator Rate 9.6 or 4.8 kspsData Rate 4.8 or 2.4 kbps

ChannelGain X

The Forward Quick Paging Channel (F-QPCH) is a type of paging channel that is used to reduce the amount of time the mobile spends monitoring the F-PCH resulting in extended battery life for the mobile. The F-QPCH contains a single bit message, quick paging indicator, to direct a mobile, operating in the so-called slotted mode, to monitor its assigned slot on the F-PCH that immediately follows. The F-QPCH uses a different modulation, so it will appear as a different physical channel.

As seen in the signal point mapping, the modulation for the F-QPCH is On-Off Keying (OOK) since the signal is ‘+1’ when the indicator is transmitted; otherwise, the signal is ‘0’ (no transmitted energy).

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1

F-PCH & F-QPCH Structure

2047 0 1 ... 15 16

F-PCH Slot n

1.28 seconds

Minimum length slot cycle of 16 slots

2

1 2 3 4 2 3 4

20msF-QPCH slot n - 80ms

......

1 2 3 4

paging indicators paging indicators

4 reserved indicators4 configuration change indicators

F-PCH

F-QPCH

80ms

F-PCH

The F-PCH protocol provides for scheduling the transmission of messages to an individual mobile station in certain assigned paging slots. We say that the mobile station operates in the slotted mode. If the mobile station monitors all paging slots, we say that the mobile is operating in the non-slotted mode.

The slotted mode saves battery life for the mobile station since the mobile can power down some of its circuitry when not monitoring the F-PCH. The mobile station calculates the paging channel slot by using the hashing algorithm specified in the IS-95/IS-2000 standard. The base station calculates the same paging channel slot from the International Mobile Station Identification (IMSI) and only transmits messages in that paging slot.

The slot cycle is a multiple of 1.28 seconds, and is specified by the slot cycle index. The length of the slot cycle, T, in units of 1.28 seconds is given by:

T = 2i

Where i is the slot cycle index. There are 16 * T slots in a slot cycle.

F-QPCH

A mobile station monitoring the F-QPCH will be notified about a page or updated overhead messages on the regular F-PCH using a 2-bit indicator about 100ms prior to the assigned slot on the F-PCH. The slot cycle structure of the F-QPCH is similar to the F-PCH structure. See the figure.

A F-QPCH slot is divided into four parts. A paging indicator is transmitted two times, in Parts 1 and 3, or Parts 2 and 4. What parts to transmit the indicator to is determined by the hashing algorithm defined in IS-2000. The purpose of the hashing algorithm is to spread out the mobile stations over the F-QPCH slot so that not every mobile is monitoring the same indicators.

If the mobile station cannot detect a paging indicator to be “OFF,” the mobile will read the F-PCH slot immediately following the F-QPCH slot. The mobile needs only to detect one indicator to be “OFF,” i.e., if the mobile detect the first indicator to be “OFF,” the second indicator does not have to be monitored.

CL8300-SG.en.UL 212



De-Multiplexing Function

De-multiplexingFunction

Overheadand user

channels,x, or xI & xQ

I-phase

Q-phase

DEMUX

YI

YQ

X

YI

YQXQ

XI

or

To Walsh function,complex scrambling,etc.

To maintain downward compatibility, the data on the forward channels is processed at the base station in a manner similar to that of the forward channels in IS-95. The primary difference is that after the channel data is scrambled by the long code, encoded, and interleaved, rather than transmitting the same data bits as I and Q components, the data bits stream is split, and alternate set of bits are transmitted as either I or Q components. This split is done in the de-multiplexing function.

It is only those channels that are generated on output, x, of the signal processing (e.g., F-FCH and F-QPCH) that will have their bit stream de-multiplexed. The other channels (e.g., F-PCH and F-SYNC) have their output defined as I and Q components, xI and xQ, and therefore do not need further multiplexing.

Transmit Diversity

The figure shows the multiplexing done if no transmit diversity is employed. If transmit diversity is used, both the I and Q components are further divided into separate streams, e.g., YQ1 and YQ2.

SR3

For SR3, instead of generating YI and YQ, the output of the de-multiplexing function is YI1, YI2, YI3, YQ1, YQ2, YQ3.

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Σ

xxBaseband

Filter

BasebandFilter

PNI PNQ

sin(2πfct)

cos(2πfct)

I

Q

s(t)

Whenenabled,

rotateby 90o

(output-Qin + jIin)

Iin

Qin

Σ

Σ

+

+

+

+

+

-

x

x

x

x

x

x

x

YI

YQ

WalshFunction

QOFsign

Walshrot Enable

Complex Multiplier Quadrature Mixer

When the channels have been de-muliplexed, the Walsh function for the channel is applied. If enabled, the Quasi-Orthogonal Function sign (QOFsign) provides a mask that when applied to the Walsh function creates quasi-orthogonal Walsh codes. The different QOFsign mask that can be used are specified in the standard.

After the Walsh function is applied, the signal can be rotated in the I and Q plane (review the constellation diagram for digital modulation in previous lesson). If the Walshrot bit is ‘0’, the no rotation is performed, otherwise the signal is rotated 90 degrees.

Note: The standard specifies a NULL QOF, which means that QOFsign = +1 and Walshrot = ‘0’. In other words, quasi-orthogonal Walsh codes are not used, and the signal is not rotated.

Complex Scrambling

The next step in the process is to perform complex multiplication, or complex scrambling, andquadrature spreading of the signal with the PN codes, PNI and PNQ (a.k.a. Pseudo-Noise Complex QPSK, or PNCQPSK). Complex scrambling is not performed in IS-95, but is needed for IS-2000 to balance the energy between the I- and Q-phase so that the peak-to-average (P/A) ratio in the RF signal is lowered. A lower P/A ratio in the RF signal typically means that more cost-effective amplifiers can be used to amplify the RF signal.

When performing complex scrambling, the I and Q components are cross-multiplied with the I and Q components of the PN code. The product is a complex number, having a real part and an imaginary part (indicated by ‘j’) that are 90 degrees apart, as shown below:

(I + jQ) x (PNI + jPNQ) = (I x PNI - Q x PNQ) + j (Q x PNI + I x PNQ)

This multiplication rotates the constellation (see the Digital Modulation topic in the CDMA Codes lesson) and thereby distributes the power evenly between the axis*.

RF Modulation

After quadrature spreading, the signal is filtered using a baseband filter, and then modulated in the frequency domain using a quadrature mixer. The modulated signal is amplified and sent to the antenna.* See: HPSK Spreading for 3G, Agilent Technologies, application note 1335

CL8300-SG.en.UL 214



Forward Link Channels Data Rates - SR1

Channel Type Data Rates [bps]

Sync Channel 1200

Paging Channel 9600 or 4800

Broadcast Control Channel19200 (40 ms slots), 9600

(80 ms slots), or 4800 (16 ms slots)

Quick Paging Channel 4800 or 2400

Common Power Control Channel 19200 (9600 per I and Q phase)


Forward Common ControlChannel

38400 (5, 10 or 20 ms frames)19200 (10, or 20 ms frames) or

9600 (20 ms frames)

Forward FCH and SupplementalCode Channel

9600, 4800, 2400 or 1200 RC1

14400, 7200, 3600 or 1800RC2

9600 x N**, 4800, 2700 or 1500

RC3Forward FCH and Forward SCH

14400 x N*, 7200, 3600 or 1800

RC4

RC5

9600 x N*, 4800, 2700 or 1500

* N = 1, 2, 4, 8, or 16** N = 1, 2, 4, 8, 16, or 32

* N = 1, 2, 4, 8, or 16** N = 1, 2, 4, 8, 16, or 32

The table shows the allowed data rates for the specified forward link channels operating with SR1.

The actual data rates used for the F-SCH depends not only on the radio configuration, but also on the size of the frame used. For the F-SCH, the lowest data rate for frames of size 40 ms and 80 ms is not 1500 bps, but 1350 bps and 1200 bps, respectively. The F-SCH with frames of size 40 ms and 80 ms also use the data rate 2400 bps instead of 2700 bps.



CL8300-SG.en.UL 215



1200

Forward Link Channels Data Rates - SR3

Channel Type Data Rates [bps]

Sync Channel

Broadcast Control Channel 19200 (40 ms slots), 9600 (80 ms slots), or 4800 (160 ms slots)

Quick Paging Channel 4800 or 2400

Common Power Control Channel 19200


Forward Common ControlChannel

38400 (5, 10 or 20 ms frames)19200 (10, or 20 ms frames) or

9600 (20 ms frames)

Forward DedicatedControl Channel

9600

9600, 14400

9600, 14400

RC6, RC7

RC8

RC9

Forward FCHand SCH

9600 x N*, 4800, 2700, 15009600 x N**, 4800, 2700, 150014400 x N*, 7200, 3600, 1800

14400 x N*** , 7200, 3600, 1800

RC6RC7RC8RC9

* N = 1, 2, 4, 8, 16, or 32** N = 1, 2, 4, 8, 16, 32, or 64*** N = 1, 2, 4, 8, 16, 32, or 72

* N = 1, 2, 4, 8, 16, or 32** N = 1, 2, 4, 8, 16, 32, or 64*** N = 1, 2, 4, 8, 16, 32, or 72

The table shows the allowed data rates for the specified forward link channels operating with SR3.

The actual data rates used for the F-SCH depends not only on the radio configuration, but also on the size of the frame used. For the F-SCH, the lowest data rate for frames of size 40 ms and 80 ms is not 1500 bps, but 1350 bps and 1200 bps, respectively. The F-SCH with frames of size 40 ms and 80 ms also use the data rate 2400 bps instead of 2700 bps.

Remember that the F-PCH is not used when operating with SR3.



CL8300-SG.en.UL 216



Multi-Carrier Mode to Implement SR3

• Main features of multi-carrier mode are:– Allows overlay of 3X with 1X or IS-95

• Maintains orthogonal modulation between 3X and 1X

– Coded information symbols are de-multiplexed among three 1.23 MHz carriers

– Frequency diversity is equivalent to spreading the signal over the entire bandwidth

– Natural transmit diversity without additional complexity at mobile• Transmit different sub-carriers on spatially separated antennas

– Allows for spectrum flexibility

• Rake receiver captures signal energy from all bands:– Each forward link channel may be allocated an identical Walsh

code on all carriers.

In order to implement SR3, IS-2000 is using the so-called multi-carrier mode. Multi-carrier mode means that the coded information symbols are multiplexed across the 1.23MHz carriers (“1X”) involved in the process – SR3 is using three carriers.

Example

SR3 is made up of the following carriers:

f1, f2, f3

The coded information symbols to be transmitted are:

sn, where n = 1, 2, …

The symbols are then multiplexed on the carriers as follows:

s1 s2 s3 s4 s5 s6 s7 …

f1 f2 f3 f1 f2 f3 f1 …

Why Multi-Carrier Mode?

The alternative to multi-carrier mode is direct-spread mode where the information symbols are spread across the entire carrier instead of multiplexed between a number of “1X” carriers. For SR3, it would be a carrier three times the bandwith of a “1X” carrier.

Multi-carrier mode is particularly important for operators with very limited spectrum license. The standard allows for flexible configurations. For example, it is possible to use SR3 for the forward link and SR1 on the reverse link. This configuration would consume the frequency spectrum equivalent of two fully frequency duplex “1X” carriers.

Another benefit with the multi-carrier mode on the forward link is that transmit diversity (TD)can easily be implemented at no additional complexity at the mobile receiver. This is accomplished by transmitting the different sub-carriers in a multi-carrier system over different spatially separated antennas. Auxiliary Pilot Channels are used for the extra antennas. The signals from the antennas fade with low correlation, which increases the effective frequency diversity. The multi-carrier receiver automatically captures this diversity by combining signals from the multiple frequency bands in a maximum-ratio-combining manner.

CL8300-SG.en.UL 217




• Long code• Walsh code• Short code

– PN offset

– Same as IS-95.

For the forward link in IS-2000, the CDMA codes used, long code, short code, and Walsh code, are used in a similar manner as they are used in IS-95. In fact, the short code is used exactly the same way: to provide identification of an antenna face by using a time-offset of the code (PN offset).

CL8300-SG.en.UL 218



Forward Link Long Code Masks

1100011001101 00000 PCN 000000000000 PILOT_PN

41 … 29 28 … 24 8 … 020 … 923 … 21

F-PCH

1100011001101 00100 BCN 000000000000 PILOT_PN

41 … 29 28 … 24 8 … 020 … 923 … 21

F-BCCH

1100011001101 10000 000 000000000000 000000000

41 … 29 28 … 24 8 … 020 … 923 … 21

F-CCCHF-CPCCH

1100011001101 01100 CACH_ID 000000000000 PILOT_PN

41 … 29 28 … 24 8 … 020 … 923 … 21

F-CACH

01 40 LSBs of VPM

41 40 39 0…


41 … 32 31 0…

F-DCCHF-FCHF-SCH


Shown are the long code masks used for the forward link channels in IS-2000.


The long code mask for the F-DCCH, F-FCH, and F-SCH is user-specific and based on the ESN of the mobile. For the user-specific long code mask, a permuted version of the ESN is used.

For example, if the ESN of the mobile has 32 bits:

x31 x30 x29 x28 … x1 x0

Then, the permuted ESN used for the long code mask would look like:

x0 x31 x22 x13 … x18 x9


For the user-specific long code mask, it is also possible to have a private mask based on encryption. The private mask is based on the 40 least significant bits (LSB) of the Voice Privacy Mask (VPM) as generated by a keygeneration procedure*.

* See: Common Cryptographic Algorithms, Revision C,1997. This is an EAR-controlled document subject torestricted distribution.

Long Code Generator

Long CodeMask

ScramblingSequence

PCN Paging Channel numberBCN Broadcast Control Channel numberCACH_ID Common Assignment Channel identifierPILOT_PN F-PICH PN offset

PCN Paging Channel numberBCN Broadcast Control Channel numberCACH_ID Common Assignment Channel identifierPILOT_PN F-PICH PN offset

CL8300-SG.en.UL 219



Forward Link Walsh Codes

• Walsh codes of length up to 256 bits can be used.– Up to 128 bits for SR1

• Reserved Walsh codes:– F-PICH

• W064

– F-SYNC• W32

64

– F-PCH• W1

64 through W764

– F-TDPICH• W16

128

– F-QPCH (SR1)• W80

128, W48128, W112

128

• Quasi-orthogonal codes are possible.

On the forward link in IS-2000, the length of the Walsh code used ranges from 4 bits to 128 bits for SR1, and 256 bits for SR3. (The Auxiliary Pilot Channels can have codes of a length up to 512 bits.)

The length of the Walsh code used often depends on the data rate of the channel. For example, if the data rate for a F-SCH (RC4) is N*9.6 kbps, then the length of the Walsh code used for that channel is 128/N. So, a F-SCH (RC4) with a data rate of 76.8 kbps (8*9.6 kbps) will have aWalsh code of length 16 (128/8).

Any of the Walsh codes that are not used for any overhead channels, other than the Pilot Channel, can be used by Traffic Channels.

IS-2000 also allows for the use of quasi-orthogonal Wlash codes to be used. See the CDMA Codes lesson for more details.

CL8300-SG.en.UL 220



Outline - 3/4





– Handoff

– Power control.

CL8300-SG.en.UL 221




0 or 1 ReverseDedicated Control

Channel

Reverse CDMA Channel for SR1 and SR3

CommonControl Channel

Operation

Traffic ChannelOperation(RC3 to 6)

AccessChannel

TrafficChannel

(RC1 or 2)

EnhancedAccess Channel

Operation

0 to 7 ReverseSupplemental

Code Channels

ReverseFundamental

ChannelEnhanced

Access Channel

ReversePilot Channel

Reverse CommonControl Channel



0 to 2 ReverseSupplemental

Channel

0 or 1 ReverseFundamental

Channel

Reverse PowerControl SubchannelIS-95 compatible IS-2000 specific

IS-95 Compatible Reverse Link Channels

To maintain compatibility with IS-95, IS-2000 uses the same reverse link channel functionalities that are used in IS-95. These channels are:

•Fundamental Channel (R-FCH)* - For low data rates and voice calls that operate in the same way as IS-95 Traffic Channels for backwards capability. Channel carries both massage and control data.

•Pilot Channel (R-PICH)* - A new channel for IS-2000 and similar to the F-PICH, it is used at the base station to provide phase reference for the received reverse link signal. The R-PICH allows the mobile to transmit at a lower power level to reduce the overall interference level.

•Access Channel (R-ACH)* - Used when the mobile must access the system to initiate communication or respond to a direct message sent from the base station. Similar to IS-95 Access Channel.

•Supplemental Code Channel (R-SCCH) – Up to seven channels are used in IS-95B to increase the data rate for a Reverse Traffic Channel.

Additional channels are specified in IS-2000. These channels will be discussed on the following pages.

* The channel is required in a IS-2000 system using spreading rate 1 to support typical voice operation.

CL8300-SG.en.UL 222



R-PICH and R-ACH

• Pilot Channel (R-PICH)– Carries the Reverse Power Control Sub-Channel

• Access Channel (R-ACH)– Same as IS-95

– Transmit access probes.

Access transmission length

AccessSlot N

AccessSlot N+1

AccessSlot N+2

20 ms R-ACH Frame

SystemTime

Preamble Message Capsule

•Pilot Channel (R-PICH) - Similar to the F-PICH, it is used for initial acquisition, time tracking, Rake-receiver coherent reference recovery, and power control measurements. The pilot channel allows the mobile to transmit at a lower power level to reduce the overall interference level. The R-PICH also has multiplexed forward Power Control (PC) information.

•Access Channel (R-ACH) - Used when the mobile station must access the system to initiatecommunication or respond to a direct message sent from the base station. The mobile transmits access probes on the R-ACH. An access probe consists of a preamble and a message capsule, both of with a length of some number of frames (20 ms), determined by the system operator. The R-ACH has the same coding and structure as the IS-95 access channel.

CL8300-SG.en.UL 223



• Enhanced Access Channel (R-EACH)– Transmit enhanced access probes

• Two operational modes– Basic Access (BA) mode

– Reservation Access (RA) mode• Data transmitted on R-CCCH

R-EACH

EnhancedAccess Header

PreambleTransmission

Tx Power

1.25 ms

EnhancedAccess Data

Reverse Pilot Channel Transmission

5 ms 20, 10, 5 ms

BA RA BA RA BA RA

The Reverse Enhanced Access Channel (R-EACH) is used by the mobile to initiate communication with the BS or to respond to a mobile directed message. The EACH can be used in two possible modes:

•Basic Access (BA) mode

•Reservation Access (RA) mode.

In BA mode, the enhanced access probe (so called Aloha Access Probe, AAP) consists of an enhanced access channel preamble, followed by enhanced access data. When operating in the BA mode, the mobile does not transmit the enhanced access header on the R-EACH.

In the RA mode, the enhanced access probe (so called Reservation Access Probe, RAP) consists of an enhanced access channel preamble, followed by an enhanced access header. Enhanced access data is sent on R-CCCH upon receiving permission from the base station over the F-CACH. The enhanced access channel header contains access information, e.g., the data rate and frame size of the enhanced access data.

CL8300-SG.en.UL 224



R-CCCH

• Common Control Channel (R-CCCH)– Sends longer data and messages without setting up dedicated

traffic channel

• Two operational modes:– Reservation Access (RA) mode

– Designated Access (DA) mode.

PreambleTransmission

Tx Power

1.25 ms

Reverse Common Control ChannelTransmission

Reverse Pilot Channel Transmission

20, 10, 5 ms

The Reverse Common Control Channel (R-CCCH) is used for the transmission of user and signaling information to the base station when reverse traffic channels are not in use. The R-CCCH differs from the R-ACH in that the R-CCCH offers extended capabilities beyond the R-ACH. The R-CCCH supports lower latency access procedures required for efficient operation of the Packet Data Suspended State. The R-CCCH can be used in one of two possible modes:

•Reservation Access (RA) mode

•Designated Access (DA) mode.

The DA mode is a mode of operation on the R-CCCH where the mobile station responds to a request received on the F-CCCH. In the DA mode, each R-CCCH is slotted, with the slot duration given by the parameter RCCCH_slots. The R-CCCH slot duration will be RCCCH_slots x 1.25 ms.

The RA mode is a mode of operation on the R-CCCH where the mobile station transmits the enhanced access data when the R-EACH operates in the RA mode. During RA mode, closed loop power control is used. The power control commands are transmitted on the F-CPCCH.

The preamble length is an integer number of 1.25 ms intervals. A zero length preamble (no preamble) is permitted. The number of 1.25 ms intervals to be used is indicated by the BS. The preamble length depends upon the rate at which the base station can search the PN sequence, cell radius, and the multipath characteristics of the cell. The base station search rate is dependent upon the hardware configuration of the cell.

The R-CCCH physical layer design for 9.6 kbps is identical to the R-ACH. Other rates available are 19.2 and 38.4 kbps, with the same design but different power requirements (3 dB and 6 dB respectively above the power setting for 9.6 kbps, depending upon the power limitations of the mobile). If the mobile is unable to supply the power to transmit with the specified access parameters, the mobile may autonomously reduce its transmission rate. If necessary due to power limitations, the mobile may also transmit on an R-ACH (if available).

CL8300-SG.en.UL 225



R-DCCH and R-SCCH

• Dedicated Control Channel (R-DCCH)– Similar to the F-DCCH

– For signaling and short messages for the SCH

• Supplemental Code Channel (R-SCCH)– For high data rate transmission, such as multimedia– Used in a similar manner as the SCH

– Identical to the same channel in IS-95B.

•Dedicated Control Channel (R-DCCH) - For signaling and short messages for the SCH and can be used instead of the FCH for signaling for data. If concurrent services (voice and data) are used, the DCCH will be used together with the data service, and the FCH will transmit the voice.

•Supplemental Code Channel (R-SCCH) - For high data rate transmission such as multimedia, and is used in a similar manner as the SCH.

CL8300-SG.en.UL 226



R-FCH and R-SCH

• Fundamental Channel (R-FCH)– For low data rates and voice calls

• Operates in the same way as IS-95 traffic channels• Carries both message and control data

• Supplemental Channel (R-SCH)– For high data rate transmission

– Carries data only• Messages must be transmitted with either FCH and/or DCCH

– Same coding as R-FCH

The Reverse Fundamental Channel (R-FCH) is used for low data rates and voice calls that operate in the same way as an IS-95 traffic channel for backwards capability. The channel carries both message and control data and supports 5 and 20 ms frames.

The 20 ms frame structures provide rates derived from IS-95 Rate Set 1 or Rate Set 2. The 5 ms frames provide 24 information bits per frame with a 16-bit CRC. Within each 20 ms frame interval, either one 20 ms R-FCH structure, up to four 5 ms R-FCH structure(s), or nothing, can be transmitted. In addition, when the 5 ms R-FCH structure is used, it can be “on” or “off” in each of the four 5 ms segments of a 20 ms frame interval.

The Reverse Supplemental Channel (R-SCH) is used for high data rate transmission, packet data or circuit data. The channel carries data only and messages must be transmitted with either the FCH and/or DCCH.

The R-SCH can be operated in two distinct modes. The first mode is used for data rates not exceeding 14.4 kbps and uses blind rate detection (no scheduling or rate information provided). In the second mode, the rate information is explicitly known by the base station (no blind rate detection is performed).

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Reverse Link Channel Types for the SR1 and SR3

Reverse Pilot Channel

Enhanced Access Channel

Reverse Common Control Channel

Reverse Dedicated Control Channel

Reverse Fundamental Channel

Reverse Supplemental Code Channel (RC1 and RC2 only)

Reverse Supplemental Channel (RC3 and RC4 only)

Spreading Rate 1

1

1

1

1

1

7

2

Spreading Rate 3

1

1

1

1

1

–

2

Channel Type Maximum No.

Access Channel 1 –

The table shows the number of possible channels that can be transmitted by each mobile for each channel type in a SR1 and SR3 system.

Channel AcronymReverse Pilot Channel R-PICHAccess Channel R-ACHEnhanced Access Channel R-EACHReverse Common Control Channel R-CCCHReverse Dedicated Control Channel R-DCCHReverse Fundamental Channel R-FCHReverse Supplemental Channel R-SCHReverse Supplemental Code Channel R-SCCH


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Reverse Link Radio Configurations

RC SR Characteristics1 1 1200, 2400, 4800, and 9600 bps data rates with R=1/3, 64-ary

orthogonal modulation (non-coherent) (IS-95, 8kbps vocoder)

2 1 1800, 3600, 7200, and 14400 bps data rates with R=1/2, 64-ary orthogonal modulation (non-coherent) (IS-95, 13kbps vocoder)

3 1 1200, 1350, 1500, 2400, 2700, 4800, 9600, 19200, 38400, 76800, and 153600 bps with R=1/4, 307200 bps with R=1/2, BPSK modulation with a pilot (cdma2000 1X, 8kbps vocoder)

4 1 1800, 3600, 7200, 14400, 28800, 57600, 115200, and 230400 bps with R=1/4, BPSK modulation with a pilot

5 3 1200, 1350, 1500, 2400, 2700, 4800, 9600, 19200, 38400, 76800, and 153600 bps with R=1/4, 307200 and 614400 bps with R=1/3, BPSK modulation with a pilot (cdma2000 3X, 8kbps vocoder)

6 3 1800, 3600, 7200, 14400, 28800, 57600, 115200, 230400, and 460800 bps with R=1/4, 1036800 bps with R=1/2, BPSK modulation with a pilot

Radio Configuration (RC) identifies the general characteristics of the radio interface, among which are:

•Data rate

•Forward error correction (FEC)

•Speech coding (vocoder rate)

•Modulation scheme.

Currently, six reverse link radio configurations (RC1 through RC6) are defined for IS-2000. The first four RCs are for the 1X spreading rate (SR), which equals 1.2288 Mchips/sec, and the last two are for the 3X spreading rate (SR3), which equals 3 x 1.2288 Mchips/sec, or 3.6864Mchips/sec. SR3 is not supported in the first phase of 3G-1X.

Radio configurations RC1 and RC2, which use the same modulation scheme as the IS-95 8kbps and 13kbps vocoders, respectively, apply to both IS-95 and IS-2000.

Note: For RC 3 and 5, the lowest data rate (“1/8 rate”) for the R-FCH is 1500 bps. The data rates of 1200 bps and 1350 bps are for the R-SCH with frames of size 80 ms and 40 ms, respectively. The R-SCH with frames of size 40 ms and 80 ms also use the data rate 2400 bps instead of 2700 bps.

CL8300-SG.en.UL 229




RelativeGains

ComplexMultiplier

R-SCH2

R-PICH

R-DCCH

R-FCH

R-SCH1/R-CCCH/R-EACH

Σ

Σ

BasebandFilterand

QuadratureMixer

LCG LCM

I’

Q’Q

I

Walsh

Walsh

Walsh

PNI PNQ

To RF modulation

Walsh

LCG Long Code GeneratorLCM Long Code Mask


The figure shows a simplified implementation of the reverse link transmit processing and its use of the various codes.

Depending on application and configuration, different channels are generated, and their respective Walsh code assigned. The R-PICH uses W0

32, which essentially is 32 zeroes, or +1 in voltage; therefore, the Walsh code assignment is not shown.

After the assignment of Walsh code, the channels have their relative gains adjusted, and are separated into the in-phase (I) and quadrature-phase (Q). The I- and Q-phases are transformed by the complex multiplier by multiplying the I and Q inputs by the output of the long code generator through the long code mask, the I-phase PN sequence (PNI), and the Q-phase PN sequence (PNQ).

The transformed I and Q streams are shaped and converted to the appropriate RF frequencies by the baseband filter and quadrature mixer. The output is then sent to further amplification and transmission on the reverse link.

Each component will be discussed in greater detail.

Note: R-ACH is coded and transmitted the same way as in IS-95. See the IS-95 Specifics lesson for more details.

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R-FCH and R-SCH - RC3



172 Bits/20n ms


1,512 Bits/20n ms3,048 Bits/20n ms6,120 Bits/20n ms


Bits16

668

12

1616161616

Data Rate(kbps)

9.6

1.52.7/n4.8/n9.6/n

19.2/n38.4/n76.8/n153.6/n307.2/n

R1/4

1/41/41/41/4

1/41/41/41/41/2

Factor2x

16x8x4x2x

1x1x1x1x1x

DeletionNone


NoneNoneNoneNoneNone

Symbols384

1,5361,5361,5361,536

1,5363,0726,144

12,28812,288

Rate (ksps)76.8

76.876.8/n76.8/n76.8/n

76.8/n153.6/n307.2/n614.4/n614.4/n

W

Add FrameQuality

Indicator



SymbolRepetition

BlockInterleaver

SymbolPuncture

ModulationSymbol

ChannelBits

The primary attribute of IS-2000 backward compatibility with IS-95 is in the use of the fundamental channels. The transmission of a voice call or a low data rate service in IS-2000 is handled the same way as in IS-95 over its traffic channel, and in this respect, the operation of the fundamental channel is similar to that of the traffic channel.

However, there are differences between IS-95 and IS-2000. Although both use 20-ms frames, IS-2000 may also use 5-ms frames for the transmission of control data when a SCH is being transmitted. Another difference is the implementation of forward power control requests. In IS-95, the mobile power control request is transmitted on the traffic channel; in IS-2000, the power control request is multiplexed on the R-PICH. See the processing for RC1 and RC2 in IS-2000 for details regarding IS-95.

R-FCH and R-SCH Processing

An example of the F-FCH and R-SCH processing for RC3 is shown in the figure. The same processing steps are used for R-FCH (RC3) and R-SCH (RC3). R-FCH only allows data rates up to 9.6 kbps.

The channel bits (voice, data, or signaling) going into the processing will first have a frame quality indicator attached so that the receiver can detect a bad frame. Next, tail bits are added to clear the encoder before the next frame enters the encoder. The encoder adds forward error correction bits to the bit stream. Depending on application, convolutional or turbo encoding is used. The symbols coming out from the encoder are then repeated and punctured to achieve the appropriate symbol rate for the block interleaver. The block interleaver will interleave the bit stream for more robust transmission.

The table shows the available processing parameters for R-FCH and R-SCH for RC3. While the processing steps are the same, the processing parameters for other radio configurations (e.g., RC4) are different.

Other Channels

Other reverse link channels, e.g., R-DCCH and R-EACH, are coded in a similar manner but with different processing parameters.

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R-PICH and Reverse Power Control Sub-Channel

Power Control Bit W

384 x NChips

PowerControl

Pilot

1 Power Control Group= 1536 x N PN chips

Pilot bits (0’s)

MUX

The R-PICH consists of a fixed reference value, a bit value of ‘0’, ‘or voltage of ‘+1’ with some gain as determined by the current configuration and power control algorithms. Multiplexed on the R-PICH is some Forward Power Control (FPC) information. This time multiplexed FPC information is referred to as the Power Control Sub-Channel.

The Power Control Sub-Channel provides information on the quality of the forward link at the rate of 1 bit (repeated) per 1.25 ms Power Control Group (PCG), and is used by the forward link channels to adjust their power.

Each 1.25 ms PCG on the R-PICH contains 1536 x N PN chips (N=1 for SR1, N=3 for SR3). The mobile transmits the pilot signal in the first 1152 x N PN chip and the Power Control Sub-Channel in the following 384 x N PN chip in each PCG on the R-PICH.

CL8300-SG.en.UL 232




Σ

xxBaseband

Filter

BasebandFilter

PNI

PNQ

sin(2πfct)

cos(2πfct)

I

Q

s(t)

Σ

Σ

+

+

+

+

+

-

x

x

x

x

Decimatorby factor

of 2

1-chipdelay

Effectivelong code

xx

x

W12

Relativegain

R-FCH

R-DCCH

R-SCH2

R-PICH


W816

W24, W6

8

x

x

x

x

Σ+

+

Σ+

+

Relativegain

Relativegain

Relativegain

+

HPSK Quadrature Mixer

W416

W12, W2

4/W2

8

After the channels have undergone necessary signal processing (encoding, symbol repetition, etc.), Walsh codes (or Walsh covers) are applied and individual channel gain assigned to each channel.

R-PICH, R-DCCH, and R-SCH2 (if used) are summed together to generate the in-phase component (I) of the transmitter signal. In a similar manner, R-FCH and R-SCH1 are summed together to form the quadrature-phase component (Q). Because the bit rates of the R-FCH and R-SCHs are higher and require different amounts of power to transmit than the R-PICH and R-DCCH, an imbalance occurs.

Complex Scrambling

To compensate for this imbalance, complex scrambling is used during spreading, where the I and Q components are cross-multiplied with the I and Q components of the PN code. The product is a complex number, having a real part and an imaginary part that are 90 degrees apart:

(I + jQ) x (PNI’ + jPNQ’) = (I x PNI’ – Q x PNQ’) + j (Q x PNI’ + I x PNQ’)

The multiplication is the same multiplication done on the forward link. However, the PN codes used, PNI’ and PNQ’, are further manipulated to generate a digital modulation technique called Hybrid Phase Shift Keying (HPSK).

The RF modulation performed using a quadrature mixer.

CL8300-SG.en.UL 233



HPSK

Σ

xxBaseband

Filter

BasebandFilter

PNI

PNQ

sin(2πfct)

cos(2πfct)

I

Q

s(t)

Σ

Σ

+

+

+

+

+

-

x

x

x

x

Decimatorby factor

of 2

1-chipdelay

Effectivelong code

xx

x

W12

Relativegain

R-FCH

R-DCCH

R-SCH2

R-PICH


W816

W24, W6

8

x

x

x

x

Σ+

+

Σ+

+

Relativegain

Relativegain

Relativegain

+

Complex multiplier

Walsh rotatorand decimator


W416

W12, W2

4/W2

8

In order to maximize the battery life for a mobile, the mobile’s amplifier has to be efficient. For the amplifier to be efficient, the peak-to-average (P/A) power ratio of the signal should be as small as possible.

In IS-95, where Offset Quadrature Phase Shift Keying (OQPSK) is used, the P/A is reduced by avoiding zero-crossings in the constellation (see Digital Modulation in the CDMA Codes lesson). However, in IS-2000 where multiple channels with different power levels are transmitted are transmitted on the I- and Q-phases, OQPSK is not suitable. Instead, a new digital modulationtechnique is introduced to reduce the zero-crossings and the P/A ratio. The modulation technique is called Hybrid Phase Shift Keying (HPSK), or Orthogonal Complex Quadrature Phase Shift Keying (OCQPSK).

HPSK is a variation on the regular complex scrambling (see forward link) that reduces, but not eliminates, zero-crossings for the signal.

Walsh Rotator

The key component in HPSK is the so-called Walsh rotator. The Walsh rotator for the I-phase is W0

2 (+1, +1) and W12 (+1, -1) for the Q-phase. With the multiplication of these two Walsh

codes, two consecutive and identical chips are separated 90o in the final constellation and the transition between them does not go through zero.

In order for the Walsh rotator to function properly, pairs of consecutive identical chips going into the complex scrambler is assumed. Therefore, on the reverse link the standard specifies even numbered Walsh codes (consists of pairs of identical bits) for the channels.

Decimator

The decimator used for the PNQ signal minimizes the so-called Multi-Access Interference. Decimation with a factor of two ensures that the signal holds its value for two chips, thereby randomizing the direction the signals phase rotation while keeping the 90o separation as generated by the Walsh rotator.

Reference: HPSK Spreading for 3G, Agilent Technologies, application note 1335

CL8300-SG.en.UL 234



Benefits of HPSK

Zero-crossings in the constellation increases the peak-to-average (P/A) power ratio of the signal. Signals with a high P/A ratio may saturate the amplifier, which in turn may cause out-of-band emission (interference outside the channel’s bandwidth). High P/A ratio also decreases the amplifier’s efficiency and therefore reduces battery life. The goal for modulation is to reduce the P/A ratio.

For a regular QPSK signal, the probability of zero-crossings for two signals with the same amplitude is 1/4. Since HPSK limits the zero-crossing to every other chip, the probability of zero-crossings is reduced to 1/8. By using other tricks, such as reducing the number of 0o phase shifts, the P/A ratio when using HPSK is reduced by up to 1.5 dB.

Reduction of the P/A ratio and more efficient amplifiers leads to a reduction of the out-of-band transmissions by almost 4 dB. This effect of HPSK modulation on reducing out-of-band transmissions is illustrated in the figure, and shows a 5-MHz bandwidth using a spectrum analyzer.

HPSK modulation is important at network bordering cells to reduce inter-network interference and better meet the legal requirements set in the host country.

CL8300-SG.en.UL 235



Reverse Link Data Rates - SR1

* N = 1, 2, 4, 8, 16, or 32** N = 1, 2, 4, 8, or 16

* N = 1, 2, 4, 8, 16, or 32** N = 1, 2, 4, 8, or 16

Data Rates [bps]Access Channel 4800Enhanced Access Channel Header 9600

Data 38400 (5, 10, or 20 ms frames), 19200 (10 or 20 ms frames), or

9600 (20 ms frames)Reverse Common Control Channel 38400 (5, 10, or 20 ms frames),

19200 (10 or 20 ms frames), or 9600 (20 ms frames)

Reverse Dedicated Control RC3 9600Channel RC4 14000 (20 ms frames) or 9600

(5 ms frames)Reverse FCH and RC1 9600, 4800, 2400, or 1200Supplemental Code Channel RC2 14400, 7200, 3600, or 1800Reverse FCH and RC3 9600 x N*, 4800, 2700, or 1500Reverse SCH RC4 14400 x N

**, 7200, 3600, or 1800

Channel Type

The table shows the allowed data rates for the specified reverse link channels operating with SR1.

Also, for the F-SCH, the lowest data rate for frames of size 40 ms and 80 ms is not 1500 bps, but 1350 bps and 1200 bps, respectively. The F-SCH with frames of size 40 ms and 80 ms also use the data rate 2400 bps instead of 2700 bps. The actual data rates used for the R-SCH depends not only on the radio configuration, but also on the size of the frame used. Also, for the R-SCH, the lowest data rate for frames of size 40 ms and 80 ms is not 1500 bps, but 1350 bps and 1200 bps, respectively. The R-SCH with frames of size 40 ms and 80 ms also use the data rate 2400 bps instead of 2700 bps.



CL8300-SG.en.UL 236



Reverse Link Data Rates - SR3

Data Rates [bps]Enhanced Access Channel Header 9600

Data 38400 (5, 10, or 20 ms frames), 19200 (10 or 20 ms frames), or

9600 (20 ms frames)Reverse Common Control Channel 38400 (5, 10, or 20 ms frames),

19200 (10 or 20 ms frames), or 9600 (20 ms frames)

Reverse Dedicated Control RC5 9600Channel RC6 14000 (20 ms frames) or 9600

(5 ms frames)Reverse FCH and RC5 9600 x N

*, 4800, 2700, or 1500

Reverse SCH RC6 1036800, 14400 x N**, 7200, 3600, or 1800

Channel Type

* N = 1, 2, 4, 8, 16, 32, or 64** N = 1, 2, 4, 8, 16, or 32

* N = 1, 2, 4, 8, 16, 32, or 64** N = 1, 2, 4, 8, 16, or 32

The table shows the allowed data rates for the specified reverse link channels operating with SR3.

The actual data rates used for the R-SCH depend not only on the radio configuration, but also on the size of the frame used. Also, for the R-SCH, the lowest data rate for frames of size 40 ms and 80 ms is not 1500 bps, but 1350 bps and 1200 bps, respectively. The R-SCH with frames of size 40 ms and 80 ms also use the data rate 2400 bps instead of 2700 bps.



CL8300-SG.en.UL 237




• Long Code• Walsh Code• Short Code

– Zero offset for quadrature spreading

– Same as IS-95.

For the reverse link in IS-2000, the long code and short code are used in a similar manner as in IS-95.

The Walsh codes are used in IS-2000 to give identities to the channels transmitted on the reverse link. In IS-95, the Walsh codes were used to perform 64-ary modulation on the reverse link. 64-ary modulation is not needed in IS-2000.

CL8300-SG.en.UL 238




110001111 ACN PCN BASE_ID PILOT_PN

41 … 33 32 … 28 8 … 024 … 927 … 25

R-ACH

110001110 EACH_ID FCCCH_ID BASE_ID SLOT_OFFSET

41 … 33 32 … 28 8 … 024 … 927 … 25

R-EACH

R-CCCH(RA/DA)

01 40 LSBs of VPM

41 40 39 0…


41 … 32 31 0…

R-CCCH(DA)

R-DCCHR-FCHR-SCH

110001101 RCCCH_ID FCCCH_ID BASE_ID PILOT_PN

41 … 33 32 … 28 8 … 024 … 927 … 25

RA Reservation Access ModeDA Designated Access ModeRA Reservation Access ModeDA Designated Access Mode

For certain channels, the long code is used to scramble and give an identity to the channel. Data scrambling is accomplished by performing modulo-2 addition of the interleaver output symbol with binary value of the long code PN chip that is valid at the start of the transmission period of that symbol. The output of the long code mask is combined with output of the long code generator to obtain the scrambling sequence.



The long code mask for the R-DCCH, R-CCCH (Designated Access Mode), R-FCH, and R-SCH is user-specific and based on the ESN of the mobile. For the user-specific long code mask, a permuted version of the ESN is used.



* See: Common Cryptographic Algorithms, Revision C, 1997.This is an EAR-controlled document subject to restricted distribution.

Long Code Generator

Long CodeMask

ScramblingSequence

ACN Access Channel numberPCN Paging Channel numberBASE_ID Base station identifierPILOT_PN F-PICH PN offsetEACH_ID R-EACH identifierFCCCH_ID F-CCCH identifierSLOT_OFFSET R-EACH slot offsetRCCCH_ID R-CCCH identifier

ACN Access Channel numberPCN Paging Channel numberBASE_ID Base station identifierPILOT_PN F-PICH PN offsetEACH_ID R-EACH identifierFCCCH_ID F-CCCH identifierSLOT_OFFSET R-EACH slot offsetRCCCH_ID R-CCCH identifier

CL8300-SG.en.UL 239



Reverse Link Walsh Codes

Channel Type Walsh Function

R-PICH W032

R-EACH W28

R-CCCH W28

R-DCCH W816

R-FCH W416

R-SCH 1 W12 or W2

4

R-SCH 2 W24 or W6

8

The reverse link physical channels are distinguished by a separate Walsh code within the mobile. The Walsh codes are used to insure orthogonality. Spectrum spreading is done with the long code, which is used to distinguish between mobiles as done in IS-95. Because only up to five channels are separated (R-PICH, R-DCCH, R-FCH, R-SCH1, and R-SCH2), Walsh codes of shorter chip lengths can be used. The Walsh codes for the reverse channels are given in the table.

Remember that for HPSK to properly work, the Walsh codes must be even-numbered. Even-numbered Walsh codes contain pairs of identical bits.

Note: The standard allows for a mobile to transmit (and receive) two SCH at the same time. However, the most common configuration is most likely using only one SCH.

CL8300-SG.en.UL 240







42 bit mask identifies user


PN Long Codes

242 - 1 bits



215 bits

Used for scrambling

64 chip offsets used to identify antenna face to the mobile

4 - 256 bits



PN Long Code

The long code gets its name from the fact that it takes about 41.4 days for the code to repeat itself. Information about the long code is broadcast to the mobile station by the Sync Channel to help the mobile lock onto the base station and helps provide separation from other base stations.

For the reverse link, the long code and the long code mask are used to identify the signal from a specific user.

PN Short Code

One of the codes used in conjunction with the Walsh code is the PN (pseudo-random noise) short code. The PN short code on the forward link is used to provide the base station with a unique identification that the mobile station uses to identify the serving base station.


Walsh Function



CL8300-SG.en.UL 241



Outline - 4/4





– Handoff

– Power control.

CL8300-SG.en.UL 242



• IS-95– Access scheme is based on a Slotted Aloha protocol

– Probes sent on R-ACH, acknowledgement (ACK) on the F-PCH• If no ACK is received, mobile increases power and tries again

• IS-2000– Using IS-95 method, if mobile monitors F-PCH

– Additional improvement using R-EACH and F/R-CCCH, if mobile monitors F-CCCH/F-BCCH

• Sending enhanced access probes with increasing power.

7.8 Reverse Access Specifics – IS-2000

Sequence

IS-95

In IS-95, R-ACH slots are non-overlapping and collisions are avoided using a very narrow demodulation window. The mobile sends access probes on the R-ACH, according to the access channel protocol, and receives acknowledgement (ACK) for the probe on the F-PCH. If no ACK is received, mobile increases the power and tries again.

The entire process of sending one message and receiving (or failing to receive) an ACK for that message on the R-ACH is an access attempt. One access attempt consists of one or more access sub-attempts. Each access sub-attempt consists of one or more access probe sequences. Each transmission in an access probe sequence is called an access probe.

IS-2000

IS-2000 uses the IS-95 access channel protocol whenever the mobile monitors the F-PCH. In order to overcome some of the limitations of the IS-95 access channel protocol, IS-2000 provides the ability to improve the access attempts by using the R-EACH and F/R-CCCH. The R-EACH is only used if the mobile monitors the F-CCCH/F-BCCH instead of the F-PCH.

A number of improvements are seen when using the R-EACH access procedure:

•Increased system capacity by require less transmit power (less interference). It is also possible to implement closed loop power control during the access process.

•Better flow control and admissions policies

•Increases throughput and reduce delay by higher data rates for access messages (9.6, 19.2, and 38.4 kbps) and shorter preamble

•Longer messages are moved to reserved channels (R-CCCH)

•Soft handoff can be used to improve access performance.

CL8300-SG.en.UL 243



R-EACH Access Procedures

• R-EACH uses two distinct access protocols:– Basic Access (BA) mode

• Similar to IS-95• Best for short messages (e.g., < 20 ms)• Open loop power adjustment

– Reservation Access (RA) mode• Best for longer messages• Closed loop power control on reverse link• Soft handoff facilitated

• Similar procedure as IS-95– Enhanced access probes (EAP), grouped into access sequences,

transmitted with increasing power

– Ec/I0 threshold has to be met before mobile transmits first EAP

– R-EACH frame is 5 ms for less collision.

When operating on the R-EACH, there are two different access protocols that can be used:

•Basic Access (BA) mode

•Reservation Access (RA) mode.

The frame size for the R-EACH can be 5, 10, or 20 ms. A lower frame size can used for less collisions of access probes. The data rate of the R-EACH is 9600, 19200, or 38400 bps. Each R-EACH is uniquely identified by a specific long code mask.

Basic Access Mode

The BA mode is very similar to the access protocol used on the R-ACH and is intended for relatively short messages. Before the mobile can transmit on the R-EACH, an Ec/I0 test must be passed. The mobile cannot transmit the first enhanced access probe (EAP) until the primary pilot’s Ec/I0 is greater than a threshold, specified in IS-2000 as EACH_ACCESS_THRESHOLD. Then, if more than one R-EACH is associated with the F-CCCH, the mobile pseudo-randomly selects the R-EACH on which to transmit the EAP.

An EAP is only sent on the R-EACH slot boundary. The EAP in BA mode consists of a preamble and enhanced access data. The enhanced access header is not sent. The base station monitors the R-EACH for EAPs. When the base station receives an EAP in the BA mode, it sends an acknowledgement on the F-CCCH.

Reservation Access Mode

RA mode is similar to the access protocol used on the R-ACH in that the EAPs are transmitted with increasing power and grouped in to sequences, but only after an Ec/I0 test has been met. For RA mode the EAP consists only of the preamble and the enhanced access header. The enhanced access data will be transmitted on the R-CCCH after the mobile has received an Early Acknowledgement Channel Assignment Message (EACAM) on the F-CACH.

During transmission of the enhanced access data on the R-CCCH, the mobile is power controlled by the base station. The F-CPCCH sends power control bits (PCB) to the mobile.

With the RA mode, it is also possible for the mobile to be in soft handoff with several base stations. Several base stations can receive the R-CCCH.

CL8300-SG.en.UL 244




• RA procedure - No soft handoff– If F-PICH exceeds a threshold, mobile transmits EAP on R-EACH– F-CACH sends EACAM upon successful EAP– Mobile transmits the data on the R-CCCH

• The mobile is power controlled by the F-CPCCH

• RA procedure – Soft handoff– In addition to above, mobile receives PCCAM on R-EACH– Multiple F-CPCCH power controls the mobile.

Preamble Header

Preamble Data (message)

EACAMF-CACH

R-EACH

R-CCCH

F-CPCCHPCB

In the Reservation Access (RA) mode, the mobile transmits enhanced access probes (EAP) on the R-EACH. Before transmission of the first EAP, the primary base station’s Ec/I0 must exceed a threshold (EACH_ACCESS_THRESHOLD). Then, if more than one R-EACH is associated with the F-CCCH, the mobile pseudo-randomly selects the R-EACH on which to transmit the EAP.

The transmission scheme of the EAPs follows the protocol used when transmitting access probes on the R-ACH. An EAP is only sent on the R-EACH slot boundary. In RA mode, the EAP consists of the preamble and the enhanced access header. Unlike the R-ACH, where the mobile transmits the data on the R-ACH, in RA mode the mobile requests a R-CCCH on which to transmit the enhanced access data.

The base station monitors the R-EACH for EAPs. When the base station receives an EAP in the RA mode, it sends an Early Acknowledgement Channel Assignment Message (EACAM) on the F-CACH. The EACAM contains the R-CCCH the mobile will use for transmission of the enhanced access data. The EACAM also contains the Common Power Control Sub-Channel (CPCSCH) on the F-CPCCH that will be used to power control the mobile during its transmission on the R-CCCH.

If supported, the mobile may report an additional pilot (PN offset) in the EAP if that pilot (or candidate) has sufficient Ec/I0 signal strength relative the primary pilot. The (primary) base station can then set up a soft handoff scenario on the R-CCCH by reporting the secondary pilot’s CPCSCH in a Power Control Channel Assignment Message (PCCAM) following the EACAM on the F-CACH. The mobile will then have to monitor the CPCSCH on two different F-CPCCH.

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7.9 Handoff Specifics – IS-2000

• Handoffs are handled in a similar way to IS-95• Handoffs between IS-2000 and IS-95 are possible• When active, the F-SCH may use a reduced Active Set

– Subset of the Active Set for FCH/DCCH.

IS-2000 is using the same handoff algorithms used in IS-95, including the dynamic thresholds introduced in IS-95B. It is possible to perform a handoff between IS-2000 and IS-95 by changing the radio configuration. This can be useful when managing resources in a system with an IS-2000 system overlaid with an IS-95 system.

When transmitting high speed data, the F-SCH can be active at the same time as the FCH or DCCH. To consume resources, the F-SCH may operate with a reduced Active Set. However, the Active Set for the F-SCH must be a subset of the Active Set for the FCH or DCCH.

For example, if the Active Set for the DCCH contains the pilots A, B, and C, then the Active Set for the F-SCH may be A, or A and B, or any other combination.

The Active Set for the R-SCH is the same as the Active Set for the FCH or DCCH.

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7.10 Power Control Specifics – IS-2000

• Reverse link power control (RPC) - Traffic Channels– Similar to IS-95

– Mobile adjusts R-PICH power, other channels relative R-PICH

• RPC open loop– Operation depends on active channels, coding, and data rate

• RPC closed loop - Outer loops – Can measure R-PICH instead of R-FCH

– R-FCH/R-DCCH and R-SCH have different outer loops

• RPC closed loop - Inner loop– Base station sends PCB every 1.25 ms [800 Hz]

– R-FCH/R-DCCH and R-SCH controlled with the same PCB• R-FCH/R-DCCH and R-SCH have the same Active Set.

Reverse link power control (RPC) for IS-2000 is similar to the RPC for IS-95. One difference is that an IS-2000 mobile transmits a constant R-PICH (unless gated transmission is used). This means that the base station receiver can measure the Ec/I0 of the R-PICH instead of the Eb/NT of the traffic channel (which will have varying data rates), e.g., R-FCH. By measuring a constant channel, RPC implementation in the base station may be simplified.

Technically, the mobile adjusts the transmit power of the R-PICH and thereafter sets the channel gain for other channels such as R-FCH and R-SCH. The specific channel gain depends on current configuration, channel coding, and data rates.

The closed loop power control consists of the inner loop and the outer loop. The outer loop power control is implementation specific but typically adjusts the closed loop power control threshold in the base station in order to maintain a desired frame error rate. The outer loop allows for separate Eb/NT control when the R-FCH/R-DCCH and R-SCH are transmitted simultaneously.

The inner loop power control consists of a fast feedback loop from the base station to the mobile. The inner loop adjusts the transmit power of the mobile by transmitting power control bits (PCB) every 1.25 ms, or with a frequency of 800 Hz. The R-FCH/R-DCCH and R-SCH are controlled with the same PCB. The IS-95 Specifics lesson discuss the randomization of the PCB location within every 1.25 ms.

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Forward Link Power Control

• Fast forward power control (FPC) at 800 Hz (total)– Outer and inner loop operation similar to RPC

– Independent FPC on both F-FCH/F-DCCH and F-SCH

• FPC outer loop– Adjusts an Eb/NT setpoint to desired received value

• FPC inner loop– Generates PCB based on comparison between measured Eb/NT

and Eb/NT setpoint

• F-FCH/F-DCCH and F-SCH have separate inner and outer loops– Total PCB frequency on R-PICH is 800 Hz

• For example, 400/400 Hz or 200/600 Hz.

A relatively fast forward power control (FPC) algorithm for the F-FCH/F-DCCH and F-SCH is used for IS-2000 system. The standards specify a fast closed loop power control at a total frequency of 800 Hz, i.e., power updates every 1.25 ms. The FPC algorithm follows a similar design as the RPC algorithm with an inner and an outer loop.

When the forward link is transmitting the F-SCH, gains for the F-FCH/F-DCCH and F-SCH are determined separately, and the mobile runs two separate outer loop algorithms (different Eb/N0targets) and two separate inner loops (generation of PCB).

The R-PICH, which carries the PCBs on the Power Control Sub-Channel, supports a total PCB frequency of 800 Hz. Since the F-FCH/F-DCCH and F-SCH have separate inner loops, the channels must share the capacity of the R-PICH. For example, if the F-FCH and F-SCH are transmitting simultaneously, the PCB frequency for F-FCH may be 400 Hz, and for F-SCH, 400 Hz.

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Reverse Link Gating - Impact on FPC

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

20 ms = 16 PCGs

R-PICHNormal operation

Gating rate =1

R-FCH

R-PICH gatingwith 1/8 rate

R-FCH gating

R-PICH gatingwith R-DCCH

Gating rate = 1/2

R-PICH gatingwith R-DCCH

Gating rate = 1/4

Pilot PCB

R-FCH R-FCH R-FCH

R-PICH Gating with R-FCH Gating

When the R-FCH (with a radio configuration of 3 or greater) transmits at 1/8 rate, the mobile may perform gating of the R-FCH, and at the same time, gating of the R-PICH. If R-FCH gating is performed, the duty cycle is 50%. A 20 ms R-FCH frame is divided into 16 power control groups (PCG), numbered 0 to 15. During R-FCH gating, the R-FCH is transmitted in PCGs 2, 3, 6, 7, 10, 11, 14, and 15, as shown in the figure.

R-PICH Gating with R-DCCH

The R-PICH can also be gated when the only channel transmitted is the R-PICH, or when only the R-DCCH is transmitted (i.e., no F/R-FCH, or F/R-SCH). During these conditions, the R-PICH gating rate can be continuous, 1/2 rate, or 1/4 rate. The R-DCCH frame is not gated.

When 1/2 rate gating is used, only the odd-numbered PCGs are transmitted. When 1/4 rate gating is used, only power control groups 3, 7, 11, and 15 are transmitted. See the figure for example of the gating rates. The gated-on and gated-off periods are arranged so that the gated-on period always comes immediately before the 5 ms frame boundary.

During transmission on the R-DCCH the R-PICH is transmitted in all PCGs but the PCBs are transmitted according to the gating rate.

Impact on Power Control

As can be seen in the figure, when the R-PICH is gated, the PCB transmitted on the R-PICH is also gated, and the effective FPC frequency is reduced down to 400 Hz for R-PCH gating or 1/2 rate R-PICH gating, and 200 Hz for 1/4 rate R-PICH gating.

Forward Power Control Sub-Channel Gating

When operating with 1/2 rate R-PICH gating, the Forward Power Control Sub-Channel is transmitted only in the even numbered PCGs. When operating with 1/4 rate R-PICH gating, the Forward Power Control Sub-Channel is transmitted only in PCGs 1, 5, 9, and 13.

When using gating other than R-PICH gating with reverse RC3 through RC6, the base station transmits the PCB in the PCG that begins (REV_PWR_CNTL_DELAY+ 1) * 1.25 ms following the end of a PCG in which the mobile station has transmitted.

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Power Control of Other Channels

• F-CPCCH is used to transmit time multiplexed Common Power Control Sub-Channels (CPCSCH)– One power control bit (PCB) per CPCSCH

– One CPCSCH power controls one R-CCCH

• Number of CPCSCH depends on number of Power Control Groups (PCG) per frame– Determines power control frequency

– Location (offset) of PCB (CPCSCH) within the PCG is pseudo-randomized.

Rate [bps]

Duration [ms]

PCGs per Frame

Number of CPCSCHs

800 1.25 16 24400 2.5 8 48200 5.0 4 96

When used, R-CCCH can be power controlled using the F-CPCCH. The base station transmits the Common Power Control Sub-Channels (CPCSCH) for the power control of multiple R-CCCHs. The CPCSCHs (one bit per CPCSCH) are time-multiplexed on F-CPCCH and is used to control one R-CCCH.

The F-CPCCH carries a number of CPCSCHs based on the number of Power Control Groups (PCG) per frame. The fewer the PCGs per frame, the lower the power control frequency. Within a PCG, the location or offset of a specific CPCSCH is pseudo-randomized using a power control bit randomization long code mask and the long code generator.

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Summary

• High speed data is implemented in IS-2000 using SCH– Burst control function (SARA)

• Radio configurations determines coding and modulation• Forward link

– Similar to IS-95

– Additional overhead channels• F-QPCH

– Complex scrambling

• Reverse link– Continuous transmission with R-PICH

– Coding similar to forward link

– HPSK used for more cost-effective amplifier.

In IS-2000, high speed data is implemented using Supplemental Channels. The maximum data rate depends on the spreading rate used. For spreading rate 3, the maximum data rate is 1,036.8 kbps. As the data rate increases, the generated interference also increases. A burst control function assures that the interference does not exceed some level. The burst control function is called Supplemental Air Resource Allocation (SARA) by Lucent Technologies.

Radio configurations are used to determine the coding characteristics and modulation parameters for Traffic Channels (FCH and SCH). It is important to realize that the radio configuration can vary between forward and reverse links.

Forward Link

The forward link in IS-2000 is similar to the forward link in IS-95, i.e., overhead channels and Traffic Channels are transmitted at the same time. Additional overhead channels are defined in IS-2000, e.g., the Forward Quick Paging Channel (F-QPCH). The new overhead channels are optional.

To balance the load between the I-phase and the Q-phase, complex scrambling (multiplication) is performed at the same time as the quadrature spreading. The modulation method is QPSK.

Reverse Link

The reverse link is different from the IS-95 reverse link. In IS-2000, the reverse link is transmitted continuously with a Reverse Pilot Channel (R-PICH), though gating of the reverse link is supported. The R-PICH is the predominant factor in keeping the reverse link interference low.

Reverse link coding of the Traffic Channel follows similar steps as the coding on the forward link. In addition to complex scrambling, a Walsh rotator is introduced, and together they form a modulation technique called Hybrid Phase Shift Keying (HPSK). HPSK reduces the peak-to-average ratio; therefore, the amplifier’s efficiency is also reduced.

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Knowledge Check

1. The primary function of the MAC protocol is to ensure that interference contributed by all the users is kept below the Total Allowable Interference Level.A. True

B. False

2. What type of traffic is the Fundamental Channel (FCH) primarily used for?A. Voice only

B. Data onlyC. Voice and low speed data

D. Voice and high speed data

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3. Reverse link signal detection at the base station is improved by a phase reference extracted from what reverse link channel?A. Dedicated Control Channel (R-DCCH)B. Reverse Pilot Channel (R-PICH)C. Enhanced Access Channel (R-EACH)D. Supplemental Channel (R-SCH)

4. The transmission of user data on a Supplemental Channel (SCH) must be accompanied by control data on either a Dedicated Control Channel (R-DCCH) or a Fundamental Channel (R-FCH).A. TrueB. False

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5. What is complex scrambling used for?A. To spread the user data and achieve processing gain

B. To compensate for imbalance between the In-phase (I) andQuadrature-phase (Q) components

C. To multiplex several traffic channels on the carrierD. To make the user data more complex

6. What power control groups (PCG) are transmitted during 1/8 rate gating of R-FCH?A. 2, 9B. 3, 7, 11, 15

C. 1, 3, 5, 7, 9, 11, 13, 15

D. 2, 3, 6, 7, 10, 11, 14, 15

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Lesson Objectives

• Explain how high speed data is implemented• Identify forward and reverse link channels• Differentiate forward and reverse link coding• Explain the signal processing steps for a Traffic Channel• Explain the benefits of complex scrambling• Identify the use of the CDMA codes.

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Outline - 1/4




• Operation specifics– Handoff

– Power control

– Pole point.

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• Same RF characteristics as IS-95 and IS-2000– Reuse RF infrastructure

• Evolution of IS-2000– Reverse Pilot Channel

– Turbo encoding

– Reverse Supplemental Channel

• Optimized for data applications– Asymmetrical data rates

– High peak forward link data rate• 2,457.6 Mbps• Time-shared by up to 59 users

– Moderate peak reverse link data rate• 153.6 kbps.

IS-856 defines an air-interface providing high speed, high capacity packet data service for wireless users. This service employs IP (Internet Protocol) for seamless data transfer over the Internet or any private IP network. Rather than using mobiles, users access the system with an Access Terminal (AT).

While the physical layer of IS-856, identifying channel encoding and channel structure, differsgreatly from IS-95 and IS-2000 (revision A), the 1.23 MHz wide RF signal is compatible with IS-95 and IS-2000. Therefore, the same RF equipment (amplifiers, filters, etc.) used to provide IS-95/IS-2000 service can also be used to provide IS-856 service.

IS-856 is optimized for data applications, giving room more flexibility in delay and frame error requirements. By not being constrained to transmit the data in real-time and without interruption, effective retransmission schemes are possible, maximizing performance. Also, experience with the Internet indicates asymmetrical data flow, where forward link data flow is much higher than reverse link data flow.

A single forward link Traffic Channel is used on each CDMA carrier designated for IS-856 operation. The Traffic Channel is time-shared by a maximum of 59 users. This means that at any one time, only one user is actively receiving data over the Traffic Channel. With only one user, there is no need for transmit power sharing as in IS-95. Therefore, the base station can transmit at full power to produce the highest carrier-to-interference (C/I) ratio possible.

Data rate is assigned based on the signal strength measured at the AT. The AT continuously monitors the C/I of the received signal, in addition to monitoring the C/I from other neighboring sectors. The sector with the highest C/I ratio may transmit the Traffic Channel to the AT.

Forward link data can be transmitted at nine different data rates, starting at 38.4 kbps and up to 2,457.6 kbps.

Many of the enhancements (over IS-95) found in IS-2000 exist in IS-856, such as the reverse link Pilot Channel for coherent detection at the base station receiver, and turbo coding of the information. The reverse link data is transmitted in successive 26.67 ms frames at data rates from 9.6 kbps to 153.6 kbps.

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IS-856 Protocol Architecture

PhysicalLayer

Physical LayerProtocol

MACLayer

Rev Traffic ChannelMAC Protocol

Access ChannelMAC Protocol

Fwd Traffic ChannelMAC Protocol

Control ChannelMAC Protocol

SecurityLayer

EncryptionProtocol

AuthenticationProtocol

Key ExchangeProtocol

SecurityProtocol

ConnectionLayerOverhead Messages

ProtocolRoute Update

ProtocolPacket Consolidation

Protocol

Connected StateProtocol

Idle StateProtocol

Initialization StateProtocol

Air Link ManagementProtocol

SessionLayer

Session ConfigurationProtocol

Address ManagementProtocol

Session ManagementProtocol

StreamLayer

StreamProtocol

ApplicationLayerLocation Update

ProtocolRadio LinkProtocol

Signaling LinkProtocol

Flow ControlProtocol

Signaling NetworkProtocol

Default SignalingApplication

Default PacketApplication

The figure shows the protocol layers that IS-856 defines. The IS-856 protocol stack fits into the OSI model’s layers 1-3. The layers include:

Application Layer: Transport of protocol messages (Default Signaling Application) and user data (Default Packet Application). The underlining principle of this layer is to increase the robustness of the IS-856 protocol stack.

The Radio Link Protocol (RLP) uses a NAK-based retransmission (once) scheme and delivers, together with TCP layers, an extremely low error rate. Instead of sequencing frames, the RLP sequences octets, which simplifies segmentation and re-assembly of the data.

Stream Layer: Multiplexing of distinct application streams and aids in the prioritization of information.

Session Layer: Address management, session configuration and management. A session is the logical connection between the user and the IP network.

Connection Layer: Link connection establishment and maintenance. The Connection Layer is comprised of a group of protocols that are optimized for packet data. Combined, they efficiently manage the IS-856 air-link, reserve resources, and prioritize each user’s traffic. They are designed to enhance the user’s experience, while at the same time bringing efficiencies to the carrier network.

Security Layer: Ensures security of the connection between the AT and the AN. It utilizes theDiffie-Helman key exchange to ensure the intended device is authenticated on the AN, and that the connection is not hijacked. The layer is not intended to encrypt the user’s data. For complete security of the user’s data, it is best to use an end-to-end method, i.e., IPSec.

MAC Layer: Procedures used to transmit and receive over Physical Layer. The layer is a key component to optimizing the efficiency of the air-link and allowing access to the network.

Physical Layer: Physical channel structure and specifications. The Physical Layer is discussed further in this lesson.

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Sending Information and Addressing

• A priority assignment is used for user data and messages– For example, retransmitted data may have higher priority

• Messages are delivered using one of two delivery methods:– Best effort

– Reliable

• ATs can be addressed in a number of ways:– Broadcast Access Terminal Identifier (BATI)

– Multicast Access Terminal Identifier (MATI)

– Unicast Access Terminal Identifier (UATI)– Random Access Terminal Identifier (RATI).

The Access Terminal (AT) and the Access Network (AN) communicate with each other using a number of protocols, or layers. The communication is done between the same protocols at the AT and AN using messages.

Each protocol has their own set of messages, but there is a general format for all messages. The format is as follows:

•Message ID: The Message ID uniquely identifies the message

•Channel: The channel on which the message can be transmitted: Control Channel, Access Channel, Forward Traffic Channel, or Reverse Traffic Channel

•Delivery method: A message can be transmitted as Reliable or Best Effort transmission

•For Best Effort transmission, the receiver does not have to acknowledge the message

•For Reliable transmission, the receiver must acknowledge each message and the transmitter must re-transmit each message if no acknowledgement is received

•Addressing mode: A message can be addressed using three different methods: broadcast, multicast, or unicast

•Broadcast Access Terminal Identifier (BATI) – Addressing all ATs

•Multicast Access Terminal Identifier (MATI) – Addressing a groups of ATs

•Unicast Access Terminal Identifier (UATI) – Addressing a unique AT

In addition to the three addressing modes, a Random Access Terminal Identifier (RATI) can be used by the AT before it is assigned a UATI.

•Priority: The priority of the message specified as a value of 0 - 255, where 0 is the highest priority. For example, retransmitted data may be assigned higher priority to ensure that the data is received and not lost forever.

•Payload: Data from or for the next higher protocol.

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Forward Link Transmission

C/I

C/I

C/I1.2M

153

k 76

k 61

4k 1

.2M

614

k 1.

2M

76k 153k 307k 614k 76k 614k 153k 1.2M

1.2M 614k 1.8M 1.2M 1.2M 1.2M 307k 1.2M

DRC

DRC

DRC

Schedulingalgorithm

Forward link data is transmitted in successive 26.67 ms frames, which are divided into sixteen 1.667 ms slots in which packets of data are transmitted:

• The transmission duration of a single packet may vary from 1 to 16 slots as a function of the data transmission rate

• Pilot and control information are multiplexed within each frame at fixed intervals

• The packet AT destination is specified within the packet

• Upon receiving the packet, the AT transmits an acknowledgement (ACK) indicating that the packet is received, and whether its data is uncorrupted.

Scheduling Algorithm

To maximize the overall sector throughput, an IS-856 system uses a scheduling algorithm that takes advantage of a multi-user pool requesting resources from the forward link – multi-user diversity. Based on the Data Rate Control (DRC) Channel reported by each AT, the scheduling algorithm will schedule data transfer with only those ATs operating in favorable RF conditions. This ensures that the data is transferred at the highest possible rate. The DRC Channel reports the desired data rate from a sector based on the received signal strength measured at the AT. ATsoperating in less favorable RF conditions are served later, hopefully when their RF conditions improve.

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Fast Best Serving Sector Selection

C/I C/I

153K 76k 153k 307k 614k 76k 614k 153k 1.2M

153k 76k 153k 307k 614k 76k 614k 153k 1.2M

DRC DRC

The DRC Channel from the AT determines the data rate the AT will receive on the forward link. The DRC Channel also determines specifically from what sector (base station) the AT would like to receive the data from.

There are no messages involved on the the DRC Channel; just channel coding. This means that an AT can rapidly change the requested data rate and the desired sector by simply changing the coding of the DRC Channel.

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Reverse Link High Speed Data

IS-856

BaseStation

MACData

AckDiversity Receiver

• Data Channel carries high speed data– Similar to IS-2000 reverse Supplemental Channel

– Data Channel also carrier traffic messages

• MAC Channel indicates transmitted reverse link data rate and desired forward link data rate

• Ack Channel acknowledges packets from the forward link.

Pilot

High speed data on the reverse link in an IS-856 system is achieved by utilizing the Data Channel. The Data Channel on the reverse link is similar to the Reverse Supplemental Channel in IS-2000 with data rates up to 153.6 kbps.

In addition to the Data Channel, the AT is also transmitting a Pilot Channel to aid the base station receiver in demodulating the reverse link. Also, a Medium Access Control (MAC) Channel is transmitted on the reverse link.

The MAC Channel has a sub-channel, Reverse Rate Indicator (RRI) Channel that notifies the receiver what data rate the Data Channel is transmitting. With the RRI Channel, the base station receiver does not have to perform “blind” rate estimation. The MAC Channel also carries the Data Rate Control (DRC) Channel.

The Ack Channel is used by the mobile to acknowledge forward link packets. The Ack Channel does not directly impact the reverse link data.

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Reverse Link Accumulative Interference

Maximum Allowable Total Interference Level

The total level of interference on the reverse RF channel is kept below the total allowable interference level by the MAC layer. The MAC layer will indicate to the ATs if they can increase or decrease their data rate.

Managing interference is important in order to maximize the reverse link data throughput and to maintain coverage. Also, forward link performance is dependent on the accurate reception of the reverse MAC Channel.

Managing RF Resources

In IS-95, where most users send voice data, management of the RF resource is relatively simple. The base station is able to handle a certain number of calls, after which additional calls are blocked. The number of calls is related to the Total Allowable Interference level.

In IS-856, where a multitude of data services are offered, each having a different data rate, the level of interference contributed from each user may differ considerably, making management of the Total Allowable Interference level more complex. This management is handled by the MAC layer.

An example of this accumulated interference and the management scheme is shown in the figure. The amount of interference introduced by each user is a function of its transmitted data rate.

In the figure, five users are illustrated each with their own data rate and duration, therefore generating different amounts of interference. The MAC layer will stack only those users who keep the total interference below the Minimum Allowable Total Interference level.

Please note that in the figure, interference levels and time durations are not shown to scale.

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Frames and Slots

0 1 2 3 7 8 9 15

System time

1 Slot

8 Slots

16 Slots

slot: 1.667 ms

1/2 frame: 13.33 ms

frame: 26.67 ms

IS-856 data is transmitted in successive 26.67 ms frames, which are divided into sixteen 1.667 ms slots in which packets of data are transmitted.

Forward Link

On the forward link, the transmission duration of a single packet may vary from 1 to 16 slots as a function of the data transmission rate. The packet destination is specified within the packet itself. Pilot and control information are inserted within each frame at fixed intervals. Upon receiving the packet, the AT transmits an acknowledge (ACK) signal, indicating that the packet is received and its data is uncorrupted.

Reverse Link

On the reverse link, the packet duration is always 16 slots, or 1 frame. The sender’s address is implicit in the user's long code mask used to code the signal. The transmission data rate is explicitly indicated on a specific reverse link channel, the Reverse Rate Indication (RRI) Channel.

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Outline - 2/4





– Power control

– Pole point.

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MediumAccessControl

ReverseActivity Bit

(RAB)DRCLock

ReversePower Control

(RPC)

Pilot Traffic Control

Forward LinkChannel

A single forward link channel is used on each CDMA carrier frequency designated for IS-856 operation. Unlike the forward link for IS-95 and IS-2000, the forward link channel for IS-856 is time-multiplexed with four channels, as shown in the figure. The four channels are:

• Pilot Channel – Similar to the forward link Pilot Channel in IS-95 or IS-2000, it is used at the AT to provide continuous time and phase reference. Each base station transmits the short PN code using Walsh code W0 (all zeros) over the Pilot Channel with a unique base station timing offset.

• Medium Access Control (MAC) Channel – Controls the ATs on the reverse link to manage the reverse link interference and performance

• Traffic Channel – Transmits the user data packets to specific ATs. There is only one AT receiving the Traffic Channel at any time.

• Control Channel – Carries control data, or overhead information, to the ATs.

The MAC Channel is further divided into three sub-channels:

• Reverse Activity Bit (RAB) Channel – Indicates to the ATs if they can increase or decrease their datarates.

• DRCLock Channel – Indicates to the ATs whether they can point their DRC Channels to that sector

• Reverse Power Control (RPC) Channel – Transmits power control commands to the active ATs.

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Transmit Power Sharing

Pilot Channel

Paging Channel

Sync Channel

Traffic Channel

Total Data

IS-95 Forward Channel StructureTime

IS-856 Forward Channel StructureTime

TransmitPower

TransmitPower

Maximum Power Maximum Power

Because the Traffic Channel is time-multiplexed between users, there is no need for transmit power sharing as in IS-95 and IS-2000. Therefore, the base station can transmit traffic data at full power to produce the highest carrier-to-noise ratio possible, allowing high data rate transmission.

Even if every channel is time-multiplexed on the forward link, that does not mean that the theaccess scheme is TDMA based. Code-based spreading (CDMA) is still done for each channel, just not in a (time) continuous fashion.

For IS-2000, data transmission is also time-shared with MAC and Pilot Channels. In contrast, not only must IS-95 or IS-2000 users served by the same sector share the base station transmit power, the base station transmit power must also be shared with the Pilot, Page, Sync Channels, and other channels, as shown in the figure.

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Forward Link Frame and Time Slot Structure

One Frame, 32,768 Chips, 26.6 ms

One Slot, 2048 Chips, 1.66 ms

Half Slot, 1024 Chips, 0.83 ms

Data 400 ChipsData 400 Chips MAC MAC64 Chips 64 Chips

Pilot96 Chips

The forward channel is transmitted within 26.67 ms frames, as opposed to 20-ms frames in IS-95. Each frame, which consists of 32,768 chips, is divided into sixteen 1.667 ms time slots with 2048 chips each, as shown in the figure. The time slots are, in turn, divided into two 1024-chip half-slots in which the transmission of the Traffic, Pilot, and MAC Channels are time-multiplexed.

When there is no traffic or control data transmitted, an idle time slot is transmitted. Even though data is not transmitted during idle time slots, the MAC and Pilot Channels are transmitted during their correct timing sequence within the idle time slot. The Pilot Channel is transmitted asunmodulated 96-chip bursts, occurring at pre-determined fixed intervals at the center of each half slot-clock period. The bursts are transmitted at the maximum power at which the cell is enabled to transmit.

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Physical Layer Packets

MAC Layer Packet1002 bits

FCS16bits

6Tail bits



FCS16bits

6Tail bits

Pad22 bits

Pad22 bits

Pad22 bits

Pad22 bits

Pad22 bits

Pad22 bits





FCS16bits

6Tail bits




FCS16bits

6Tail bits

1024-bit Packet

2048-bit Packet

3072-bit Packet

4096-bit Packet

User data and Control Channel data are transmitted in physical layer packets over the air-interface. The bit size of the forward Traffic Channel packets is a function of the selected rate and varies from 1024 (1k) bits to 4096 (4k) bits. As shown, the bit size of the Traffic Channel packets received from the MAC layer is fixed at 1002 bits.

Regardless of the size of the packet to be transmitted, a Frame Check Sequence (FCS) is performed on the 1002-bit packets received from the MAC layer. The FCS is a Cyclic Redundancy Check (CRC). When a physical layer packet is to be transmitted, the 16-bit CRC value is concatenated with a 6-bit tail bit sequence at the end of the packet. The six tail bits (all zeroes) ensures that the encoder’s shift-registers are reset after the packet has passed through.

The AT receiving the packet will perform its own CRC calculation on the transmitted physical layer packet to validate the correctness of the packet. If the 16-bit CRC value computed by the AT matches the 16-bit CRC value transmitted in the physical layer packet, there is a high probability that the packet received by the AT is uncorrupted.

When a 2048-bit (2k), 3072-bit (3k), or 4096-bit packet is transmitted, 2, 3, or 4 MAC layer packets are concatenated together to form a single physical layer packet. A single FCS is calculated regardless of the number of MAC layer packets encapsulated in the physical layer packet, resulting in one 16-bit CRC value which is tacked on to end of the physical layer packet before the 6 tail bits. To fill the physical layer packet to its appropriate 2k, 3k, and 4k bit sizes, 22-bit padding (pads) are inserted after the 1002-bit MAC layer packets. The 22 bit pads are encoded as “0” bits, and ignored by the AT.

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Data Rates and Packet Sizes

Data rate [kbps]

Bits / packet

Preamble chips

Number of slots

38.4 1024 1024 1676.8 1024 512 8

153.6 1024 256 4307.2 1024 128 2307.2 2048 64 4614.4 1024 128 1614.4 2048 64 2921.6 3072 64 2

1228.8 2048 64 11228.8 4096 64 21843.2 3072 64 12457.6 4096 64 1

CharacteristicsData rate

[kbps]Bits /

packetPreamble

chipsNumber of slots

38.4 1024 1024 1676.8 1024 512 8

153.6 1024 256 4307.2 1024 128 2307.2 2048 64 4614.4 1024 128 1614.4 2048 64 2921.6 3072 64 2

1228.8 2048 64 11228.8 4096 64 21843.2 3072 64 12457.6 4096 64 1

Characteristics

There are nine different data rates available on the forward link for an IS-856 system, ranging from 38.4 kbps to 2457.6 kbps (2.4 Mbps). User data is transmitted in packets over the air interface and re-assembled at the AT by the Radio Link Protocol (RLP). The number of bits in each packet depends on the data rate transmitted, and is shown in the table.

Also shown in the table is how many 1.667 ms slots a packet is transmitted over. The number of slots needed is related to the desired data rate and the number of bits per packet:

Data rate [kbps] = (bits/packet) / (number of slots * 1.667 ms)

The preamble is used to identify to which AT the packet is intended, and to aid the AT in synchronization to the packet.

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Packet Preamble

Preamble400 chips

Preamble624 chips

MAC64 Chips

Pilot96 Chips

Half slot Half slot

Start packet data transmission

Repeated data transmission sequence if required

Slot period

16 slots,32,768 chips

Time

38.4 kbps example38.4 kbps example

In order for the AT to identify a packet addressed to that particular AT, and to assist the AT in synchronizing to the changing data rates, a sequence of preamble chips is transmitted prior to each Traffic and Control Channel packet.

The preamble sequence is covered by a 32-chip bi-orthogonal sequence based on the MACIndex. A MACIndex in turn, is derived from a Walsh function of length 64. MACIndex is discussed later. The 32 chip bi-orthogonal sequence is repeated at least once depending on the transmit data rate. For example, to provide a 1024-chip preamble length required for a 38.4 kbps data rate, the 32-chip preamble sequence is repeated 32 times.

The preamble chips are inserted within the data portion of the slot clock period prior to the start of the packet transmission. The figure shows the preamble (1024 chips) for a data rate of 38.4 kbps. If the total number of preamble chips to be inserted exceeds the 400-chip data portion of the half-slot period, as is the case for data rates of 38.4 kbps, the preamble chips are time-multiplexed with the MAC and pilot chips.

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Multi-Slot Transmission – Normal Termination

n n+1 n+2 n+4 n+5 n+6 n+7 n+8 n+9 n+10 n+11 n+12 n+13 n+14 n+15n+3Slot

Forward Traffic Dataor Control Channel

ReverseDynamicRate ControlSub-Channel

Reverse ACKChannel

DRC Request for 153.6 kbps

Rate

NAK NAK NAK ACKor

NAK

n n+1 n+2 n+4 n+5 n+6 n+7 n+8 n+9 n+10 n+11 n+12 n+13 n+14 n+15n+3Slot n-1


When data is transmitted at a data rate that is allotted for multiple-slot packet transmission (physical layer packet transmitted over more than one slot), a 1-to-4 slot data interlacing pattern is used. In this scheme, each packet allotted for multi-slot transmission is transmitted every fourth slot.

The three time-slot spacing between successive slots transmitting the packet is required to allow the base station to receive acknowledgement from the AT. The acknowledgement indicates if the AT has successfully received the packet (ACK) or not (NAK).

If the base station did not receive a positive acknowledgement (ACK) after the last slot for that particular packet, the packet was received in error and the AT would have to request an RLP retransmission.

A high packet error rate (PER) reduces the performance of the forward link.

Note: The reason the base station did not receive an ACK could be because the AT did not receive the package, but it could also be because the base station did not “hear” the ACK even though the AT sent the ACK.

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Multi-Slot Transmission – Early Termination

n n+1 n+2 n+4 n+5 n+6 n+7 n+8 n+9 n+10 n+11 n+12 n+13 n+14 n+15n+3Slot

Forward Traffic Dataor Control Channel

ReverseDynamicRate ControlSub-Channel

Reverse ACKChannel

DRC Request for 153.6 kbps

Rate

NAK NAK ACK NAK

n n+1 n+2 n+4 n+5 n+6 n+7 n+8 n+9 n+10 n+11 n+12 n+13 n+14 n+15n+3Slot n-1

Initiate firstpacket

transmission

Initiate secondpacket

transmission


Since the packet, when transmitted, has undergone FEC encoding, there is a redundancy of the information built into the transmitted data. If the AT could validate the correctness of the packet before the last transmitted slot for a particular packet, this means that the AT has received the full packet due to the redundancy of information. The AT would send an ACK before all slots for that packet have been used. This is called an early termination.

In the case of an early termination, the base station cancels transmission of the packet during the remaining slots for that packet, and in their place initiates the transmission of a new packet. Early terminations obviously allow more packets to be transmitted, and thereby increase the forward link throughput.

CL8300-SG.en.UL 275



Control Channel

13.33 msData Channel MAC Channel Pilot Channel

Traffic Channel Traffic ChannelControl Channel Control Channel

426.67 ms

The Control Channel transmits broadcast messages and AT-directed messages with a data rate of 76.8 kbps or 38.4 kbps. From a coding perspective, the Control Channel is the same as the Forward Traffic Channel.

Control Channel packets are transmitted in either a synchronous capsule, which is transmitted at the beginning of a Control Channel cycle, or in an asynchronous capsule, which is transmitted at any time except when a synchronous capsule is transmitted.

The Control Channel cycle is defined as a 256 slot (each slot is 1.667 ms) period synchronous with system time. In other words, each Control Channel cycle is 426.66…ms long. Thus, synchronous Control Channel capsules always occur at the start of the 426.66…ms Control Channel cycle.

The control channel is eight slots wide, and in the same manner as the Traffic Channel, each slot is divided into two 1024-chip half-slots in which the transmission of the control data, Pilot Channel, and MAC Channel are time-multiplexed.

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Sleep State

• AT transitions from Sleep State to Monitor State to monitor the Control Channel– Every 5.12 seconds, or every 12th Control Channel cycle

– Hash function determines what Control Channel cycle to monitor

• Can reduce power consumption for the AT.

0 1 3 4 5 6 7 8 9 10 11

5.12 seconds

2 ……

426.66…ms

Similar to the slotted mode in IS-95/IS-2000 where a mobile monitors the Page Channel at certain intervals (once every slot cycle), an IS-856 AT monitors the Control Channel in intervals. The AT operates in the Sleep State. The Sleep State is similar to the IS-95/IS-2000 slotted mode on the Page Channel with a slot cycle of 5.12 seconds.

When the AT operates in the Sleep State, it may stop monitoring the Control Channel and shut down processing resources to reduce power consumption, hence increasing battery life.

The base station and the AT transition from the Sleep State to the Monitor State (actively monitor the Control Channel) in time to send and receive, respectively, the synchronous capsule sent in the Control Channel cycle (every 5.12 seconds).

There are 12 Control Channel cycles within 5.12 seconds. The AT’s UATI is used with a hash function to determine which one one of the 12 Control Channel cycles the AT is monitoring.

CL8300-SG.en.UL 277



Forward MAC Channel

• Reverse Activity (RA) Channel– Transmits a Reverse Activity Bit (RAB) stream– RAB stream and random function at the AT determines reverse

link data rate– The RA Channel can be used to control reverse link interference

• DRCLock Channel– Informs an AT if it can point its DRC (Data Rate Control) Channel

to that specific sector

• Reverse Power Control (RPC) Channel– Transmits a RPC bit stream to instructs AT to power up or down

• RPC Channel vs. DRCLock Channel– RPC Channel is transmitted whenever the DRCLock Channel is

not • DRCLock interval specified by DRCLockPeriod

– Data rate of the RPC Channel is 600×(1-1/DRCLockPeriod) bps.

RA Channel

For the reverse link, there are five possible data rates: 9.6, 19.2, 38.4, 76.8 and 153.6 kbps. The actual data rate on the reverse link is determined by the AN and a random function at the AT.

The forward link has a Reverse Activity (RA) Channel that transmits a Reverse Activity Bit (RAB) stream. The RA Channel is used to tell the AT to adjust its reverse link rate. If all the sectors in the Active Set set the RAB to '0', the AT may double the rate up to an upper limit. If at least one sector in the Active Set sets the RAB to '1', the AT must reduce its transmit rate by half. The lowest data rate is 9.6 kbps.

The RA Channel can be used to control reverse link interference.

DRCLock Channel

The DRCLock Channel is used to inform an AT that the base station cannot decode the AT’s DRC (Data Rate Control) Channel. If an AT receives a DRCLock bit on the DRCLock Channel that is set to ‘0’ from the sector to which it is pointing its DRC, the AT will stop pointing its DRC at that sector.

RPC Channel

Each AT with an open connection is assigned a Reverse Power Control (RPC) Channel. The RPC Channel is used for the transmission of the RPC bit stream (similar to the Power Control Bits, PCB, in IS-95) destined to a particular AT. What RPC bit stream value to transmit is determined by the Reverse Power Control algorithm.

RPC Channel vs. DRCLock Channel

The RPC Channel and the DRCLock Channel are time-division multiplexed and transmitted on the same MAC Channel. The RPC Channel is transmitted whenever the DRCLock Channel is not transmitted. The DRCLock is transmitted with an interval specified by DRCLockPeriod(default 16 slots).

Because the RPC Channel and the DRCLock Channel are multiplexed on the MAC Channel, the data rate of the RPC is 600 × (1 -1/DRCLockPeriod) bps.

CL8300-SG.en.UL 278




TDMFunction

PNI PNQ

TDM Time Division MultiplexTDM Time Division Multiplex

To RF modulation

Traffic /Control

Preamble

MAC

Pilot

ComplexMultiplier

BasebandFilterand

QuadratureMixer

The figure shows an overview of the IS-856 forward physical link structure for base station transmission. The components will be discussed in more detail in this lesson.

1. First, the channels are generated using their specific signal processing.

2. The TDM function multiplexes the generated channels so that only one channel is (or preamble) is transmitting at any time.

3. The output is then multiplied by the I- and Q-phase PN sequences, as provided by the complex multiplier function, or complex scrambling.

4. Finally, the I- and Q-phases are shaped and converted to the appropriate RF frequencies by thebaseband filter and quadrature mixer.

CL8300-SG.en.UL 279



Pilot Channel and Preamble

192 PNChips

per Slotfor Pilot

0 +11 1

→ → −

Pilot Channel(All 0’s)

Walsh Cover 0

0

SequenceRepetition

0 +11 1

→ → −

Preamble(All 0’s)

32-Symbol Bi-Orthogonal Coverwith MACIndex i

0

XI

XQ

XI

XQ

Pilot Channel

The Pilot Channel consist of all ‘0’ symbols (+1 in voltage) transmitted on the I-phase with Walsh cover 0. The Pilot Channel is used by the AT for initial acquisition, phase recovery, timing recovery, and maximal-ratio combining. An additional function of the Pilot Channel is to provide the AT with a means of predicting the received C/I ratio for the purpose of AT-directed forward data rate control (DRC) functionality of the Data Channel.

Preamble

The preamble is transmitted prior to each Traffic Channel and Control Channel packet. The purpose of the preamble is to identify to which AT the packet is addressed, or to identify if it is a Control Channel packet.

The addressing is done by covering the preamble with a 32-symbol, bi-orthogonal sequence based on the particular MAXIndex assigned to the AT (or Control Channel). Depending on the data rate of the packet, the bi-orthogonal sequence may have to be repeated to achieve the specific preamble length for that data rate. For example, if the preamble must be 1024 bits, then the preamble is repeated 32 times.

CL8300-SG.en.UL 280



MAC Channel

SequenceRepetition

(Factor = 4)

I Channel forEven MACIndexQ Channel for

Odd MACIndex

256 PNChips

per Slotfor MAC

WalshChip LevelSummer

RAChannel

Gain

0 +11 1

→ → −

0 +11 1

→ → −

0 +11 1

→ → −

TDMMAC Channel

DRCLocksymbols for MACIndex I

MAC ChannelRA Bits

MAC ChannelRPC Bits

for MACIndex i

RPCChannel

Gain

DRCLockChannel

Gain:

BitRepetition

BitRepetition

64-ary Walsh Cover for MACIndex i

Walsh Cover W264

I

I

Q

XI

XQ

i

The MAC Channel consists of three sub-channels: Reverse Power Control (RPC) Channel,DRCLock Channel, and Reverse Activity (RA) Channel. Each MAC Channel symbol is BPSK-modulated on one of 64 64-ary Walsh code words (covers). BPSK modulation means that depending on the MAC Channel bit to be transmitted, the chip sequence transmitted is either the regular Walsh cover (if bit is ‘0’) or the inverse (if bit is ‘1’). The MAC symbol Walsh covers is transmitted four times per slot in bursts of 64 chips each, sequence repetition.

MAC Channels with even-numbered MACIndex values are assigned to the I-phase, while those with odd-numbered MACIndex values are assigned to the Q-phase.

Since 64-ary Walsh covers are used in the coding process, 64 MAC indices can be used. However, for the MAC Channel, only 60 indices are used: MACIndex of 4 (Walsh function W2

64) is used for the RA Channel, and MACIndex 5 through 63 used for the Traffic Channels, one for each active AT.

Every AT with an open connection is assigned to one of the available MAC Indices. The MAC Channel is used for the transmission of the RPC bit stream and DRCLock information for that specific MACIndex. The RPC Channel and the DRCLock Channel are time-division multiplexed (TDM) and transmitted on the same MAC Channel. The TDM scheme is determined by the DRCLockPeriod and DRCLockLength parameters (determines frequency and duration of the DRCLock information) specified by the network.

The RA Channel transmits a Reverse Activity Bit (RAB) stream. The network decides the length of the stream for one RAB. Depending on the length, the RAB needs to be repeated a number of times to achieve the correct number of bits in the sequence.

CL8300-SG.en.UL 281



Traffic and Control Channel

ForwardChannel or

Control ChannelPhysical Layer

Packets

EncoderR = 1/3or 1/5

QPSK/8-PSK/16-QAM

ChannelInterleaver

Scrambler 16 Channels

SequenceRepetition/

SymbolPuncturing

SymbolDEMUX1 to 16

16-aryWalshCovers

WalshChannel

Gain = 1/4

WalshChip LevelSummer

I

I I I I I

Q

Q Q Q Q Q

C

C

D

D

XI

XQ0 to 15

The forward Traffic Channel and Control Channel data are encoded in blocks called physical layer packets. There is no physical difference between a Traffic Channel packet and a Control Channel packet. The output of the turbo encoder is scrambled and then fed into a channelinterleaver.

Unlike IS-95 and IS-2000, the scrambler on the forward link for IS-856 does not use the long code. Instead, the scrambler is using a 17-tap linear feedback shift-registers, whose initial state depends on the MACIndex and data rate of the packet to be coded. The scrambler is further covered in the section discussing forward link CDMA codes.

The output of the channel interleaver is fed into a modulator. The digital signal modulator performs QPSK, 8-PSK, or 16-QAM modulation. The modulated symbol sequences are then repeated and punctured as necessary.

The resulting sequences of modulation symbols are then demultiplexed (DEMUX) to form 16 pairs (in-phase, I, and quadrature-phase, Q) of parallel streams, Ik and Qk (k = 0, 1, 2,…, 15), for I- and Q-phase, respectively. Ik and Qk are and covered with the kth Walsh channel, Wk

16 (k = 0, 1, 2,…, 15). The modulation values associated with the I- and Q-phase components of the same Walsh channel are referred to as Walsh symbols.

The gain for each Walsh channel is reduced to 1/4 in order to achieve correct total gain for the entire packet. The Walsh-coded symbols of all the Walsh channels (streams) are summed together to form a single I-phase stream and a single Q-phase stream at a chip rate of 1.2288Mcps.

The I- and Q-phase streams are then fed into the channel multiplexer, or TDM function.

Note: The tail bits needed to clear the encoder’s registers are embedded in the physical layer packet.

CL8300-SG.en.UL 282



Data rate [kbps]

Digital modulation

Preamble chips

Code rate

38.4 QPSK 1024 1/576.8 QPSK 512 1/5

153.6 QPSK 256 1/5307.2 QPSK 128 1/5307.2 QPSK 64 1/3614.4 QPSK 128 1/3614.4 QPSK 64 1/3921.6 8PSK 64 1/3

1228.8 QPSK 64 1/31228.8 16QAM 64 1/31843.2 8PSK 64 1/32457.6 16QAM 64 1/3

CharacteristicsData rate

[kbps]Digital

modulationPreamble

chipsCode rate

38.4 QPSK 1024 1/576.8 QPSK 512 1/5

153.6 QPSK 256 1/5307.2 QPSK 128 1/5307.2 QPSK 64 1/3614.4 QPSK 128 1/3614.4 QPSK 64 1/3921.6 8PSK 64 1/3

1228.8 QPSK 64 1/31228.8 16QAM 64 1/31843.2 8PSK 64 1/32457.6 16QAM 64 1/3

Characteristics

Forward Link Coding Parameters

The different data rates available in IS-856 are achieved by varying the transmitted signal modulation scheme via forward link adaptive modulation and turbo code rate, as shown in the table. The data rates used for a particular transmission are determined by the current channel conditions experienced at the AT receiver. Each data rate is associated with a particular packet bit size and modulation type.

CL8300-SG.en.UL 283



Digital Modulation – QPSK and 8-PSK

QPSK 8-PSK

Q Component

I Component

0001

0111

Q Component

I Component

001011

000

100

101111

110

010

c

-c

c-c

s

s-s

-s

c = cos( /8)πs = sin ( /8)π

Depending on the number of bits in the physical layer packet, different types of digital modulation are used:

•1024 bits per packet – QPSK (Quadrature Phase Shift Keying)

•2048 bits per packet – QPSK

•3072 bits per packet – 8-PSK (8-ary Phase Shift Keying)

•4096 bits per packet – 16-QAM (16-ary Quardature Phase Shift/Amplitude Modulation).

QPSK

With QPSK modulation, transmitted data bits are distinguished by 90-degree phase separation in the constellation diagram. This yields four distinct states, representing 00, 01, 10, and 11, thus producing a 2-bit symbol per chip cycle. This modulation scheme is illustrated by the constellation diagram shown in the figure. The four points in the diagram are obtained by resolving the in-phase (I) and quadrature-phase (Q) components.

8-PSK

8-PSK produces a 3-bit symbol per cycle. This is done in a manner similar to QPSK. In this case, the 8-PSK modulation scheme distinguishes 3-bit symbols by 45-degree phase separation to yield eight states, representing 000, 001, 010, 011, 100, 101, 110, and 111. This modulation scheme is illustrated by the constellation diagram shown in the figure. The eight points on this drawing are obtained by resolving the I- and Q-phase components.

CL8300-SG.en.UL 284



Digital Modulation – 16-QAM

16-QAM

Q Component

I Component

0000

0100

0100

1000

0010

0110

1110

1010

0011

0111

0111

1011

0001

0101

0100

1001

3A

A

-A

-3A

-3A -A A 3A

A = 1/ 10

16-QAM

The 16-QAM produces a 4-bit symbol per cycle. The 16-QAM modulation scheme uses a combination of QPSK and amplitude modulation resulting in a 4-bit symbol. This modulation scheme can be illustrated by the constellation diagram shown in the figure. The 16 points on this drawing are obtained by resolving the I- and Q-phase components.

CL8300-SG.en.UL 285




Σ

xxBaseband

Filter

BasebandFilter

PNI PNQ

sin(2πfct)

cos(2πfct)

I’

Q’

s(t)TDMfunction

I

Q

Σ

Σ

+

+

+

+

+

-

x

x

x

x

Complex Multiplier

XI

XQ

Pilot,Preamble,

MAC,Traffic, and

Control

Quadrature Mixer

The forward link consists of slots of length 2048 chips (1.667 ms). Groups of 16 slots constitutes a frame and are aligned to the zero-offset PN sequences, and align to system time on even-second ticks. The preamble, Pilot, MAC, Traffic, and Control Channels are time-multiplexed on the forward link.

The resultant sequence of chips is then sent to the quadrature spreading operation, or complex scrambling.

Complex Scrambling

The next step in the process is to perform complex multiplication, or complex scrambling, andquadrature spreading of the signal with the PN codes, PNI and PNQ (a.k.a. Pseudo-Noise Complex QPSK, or PNCQPSK). Complex scrambling is not performed in IS-95, but is needed for IS-856 (and IS-2000) to balance the energy between the I- and Q-phase so that the peak-to-average (P/A) ratio in the RF signal is lowered. A lower P/A ratio in the RF signal typically means that more cost-effective amplifiers can be used to amplify the RF signal.

When performing complex scrambling, the I and Q components are cross-multiplied with the I and Q components of the PN code. The product is a complex number, having a real part and an imaginary part (indicated by ‘j’) that are 90 degrees apart, as shown below.

(I + jQ) x (PNI + jPNQ) = (I x PNI - Q x PNQ) + j (Q x PNI + I x PNQ)

This multiplication rotates the constellation (see the Digital Modulation topic in the CDMA Codes lesson) and thereby distributes the power evenly between the axis*.

RF Modulation

After quadrature spreading, the signal is filtered, using a baseband filter, and then modulated in the frequency domain using a quadrature mixer. The modulated signal is amplified and sent to the antenna.

* See: HPSK Spreading for 3G, Agilent Technologies, application note 1335

CL8300-SG.en.UL 286




• Long code– Not used for forward link

– Scrambling done by another code

• Walsh code• Short code

– PN offset– Same as IS-95.

For the forward link in IS-856, the CDMA codes used, short code and Walsh code, are used in a similar manner as in IS-95. In fact, the short code is used exactly the same way: To provide identification of an antenna face by using a time-offset of the code (PN offset).

The long code is not used on the forward link in IS-856. Scrambling is done for the Forward Traffic Channel, but not by using the 242-1 long code.

CL8300-SG.en.UL 287



Forward Link Scrambling

• Long code is not used for the forward link• Scrambling sequence generator is a 17-tap linear

feedback shift-register– Initial shift-register state depends on MACIndex and data rate.

+

Scrambling sequence

When scrambling the Traffic Channel and Control Channel, the regular 242-1 bit long code is notused on the forward link. Instead, IS-856 specifies a 17-tap linear feedback shift-register with a generator sequence of h(D) = D17 + D14 + 1, as shown in the figure.

At the start of each physical layer packet, the shift register is initialized to the state:

[ 1 1 1 1 1 1 1 r5 r4 r3 r2 r1 r0 d3 d2 d1 d0 ]

The rn bits (n = 0..5) are equal to the 6-bit preamble MACIndex value (0 to 63) and the dn bits (n = 0..3) are determined by the data rate. See table.

The initial state generates the first scrambling bit, and then the shift registers are clocked once for every encoder output code symbol to generate each bit of the scrambling sequence. Then every encoder output code symbol is modulo-2 added (XOR) with the corresponding bit of the scrambling sequence to yield a scrambled encoded bit.

Rate [kbps]

Packet length [slots] d3 d2 d1 d0

38.4 16 0 0 0 176.8 8 0 0 1 0

153.6 4 0 0 1 1307.2 2 0 1 0 0307.2 4 0 1 0 1614.4 1 0 1 1 0614.4 2 0 1 1 1921.6 2 1 0 0 0

1228.8 1 1 0 0 11228.8 2 1 0 1 01843.2 1 1 0 1 12457.6 1 1 1 0 0

Rate [kbps]

Packet length [slots] d3 d2 d1 d0

38.4 16 0 0 0 176.8 8 0 0 1 0

153.6 4 0 0 1 1307.2 2 0 1 0 0307.2 4 0 1 0 1614.4 1 0 1 1 0614.4 2 0 1 1 1921.6 2 1 0 0 0

1228.8 1 1 0 0 11228.8 2 1 0 1 01843.2 1 1 0 1 12457.6 1 1 1 0 0

CL8300-SG.en.UL 288



MACIndex vs. Walsh Codes

• MACIndex is used to address a channel to a specific user– Total of 64 indices

– 59 can be used for active users

• MACIndex is mapped to a Walsh function (code)– MAC Channel uses W64 based on MACIndex

– Preamble uses W32 based on MACIndex.

MACIndex MAC Channel Preamble0 or 1 Not used Not used

2 Not usedControl Channel

(76.8 kbps)

3 Not usedControl Channel

(38.4 kbps)4 RA Channel Not used

5-63RPC and DRCLock

ChannelsTraffic Channel

The table shows the use of the MACIndex when using the MAC Channel and the Traffic/Control Channel. The MAC, Reverse Activity (RA), Reverse Power Control (RPC), and DRCLockChannels are discussed in the reverse link part of this lesson.

Note: Only 59 indices (5 to 63) are available for Traffic Channels. That means that the maximum number of active (transmitting and receiving) users is 59 users per sector and carrier.

MAC Channel

The forward MAC Channel is composed of Walsh channels that are orthogonally covered and BPSK-modulated on a particular phase of the carrier, either In-phase or Quadrature phase. Each Walsh channel is identified by a MACIndex value that is between 0 and 63, and defines a unique 64-ary Walsh cover and modulation phase. The Walsh functions assigned to the MACIndexvalues are as follows:

Wi/264 for i = 0, 2,…, 62

W(i-1)/2+3264 for i = 1, 3,…, 63

where i is the MACIndex value. Even-numbered MACIndex values are assigned to the I-phase, odd-numbered MACIndex values are assigned to the Q-phase.

Preamble

The preamble consists of all ‘0’ symbols transmitted on the In-phase component only, and is time multiplexed into the Forward Traffic Channel stream. The preamble sequence is covered by a 32-chip bi-orthogonal sequence. The sequence is repeated several times, depending on the transmit mode. The bi-orthogonal sequence is specified in terms of the 32-ary Walsh functions and their bit-by-bit complements as:

Wi/232 for i = 0, 2,…, 62

[W(i-1)/232]’ for i = 1, 3,…, 63

where i is the MACIndex value and [W32]’ is i the bit-by-bit complement of the 32-chip Walsh function of order i.

CL8300-SG.en.UL 289



Outline - 3/4





– Power control

– Pole point.

CL8300-SG.en.UL 290




MediumAccessControl

ReverseRate Indicator

(RRI)

DataRate Control

(DRC)

Pilot Data ACK Pilot Data

Reverse LinkChannel

TrafficChannel

AccessChannel

The reverse channel structure consists of a Traffic Channel and an Access Channel, as shown in the figure. As in IS-2000, the IS-856 reverse link provides a Pilot Channel, permitting coherent detection by the base station on the reverse link and ultimately allows the AT to transmit at a lower power level to reduce the overall interference level.

Access Channel

The Access Channel is similar to the IS-95 Access Channel and used when the AT must access the system to initiate communication or respond to a message sent from the base station. The Access Channel is divided into two sub-channels:

•Pilot Channel - Similar to the forward link Pilot Channel, it is used at the base station to provide phase reference for the received reverse link signal

•Data Channel – Carries the messages for the Access Channel.

Traffic Channel

The Traffic Channel is used to carry the user data on the reverse link. The Traffic Channel is divided into four sub-channels:

•Pilot Channel - Same purpose as the Pilot Channel for the Access Channel

•Medium Access Control (MAC) Channel

•Acknowledgement (ACK) Channel - Informs the base station if a physical layer packet has been successfully received

•Data Channel - Channel carries both massage and control data. The data is transmitted in successive 26.67 ms frames at five different data rates ranging from 9.6 kbps to 153.6 kbps.

The MAC Channel is further divided into two sub-channels for transmission data rate control:

•Reverse Rate Indicator (RRI) Channel - Indicates what data rate the Data Channel is transmitting

•Data Rate Control Data (DRC) Channel - Informs a specific sector with what data rate the AT would like to receive the forward link Traffic Channel.

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Reverse Sub-Channels

Q-PhaseReverseDynamic

Rate ControlSub-Channel

Q-PhaseData Traffic

Packets

I-PhaseAcknowledge

(ACK)Sub-Channel

I-PhasePilot/RRI

Sub-Channel

RRI 256 chips

1 Slot, 2048 Chips

Pilot Sub-Channel1,793 chips

Frame = 16 Slots, 26.67 ms

1.67 ms

Unlike the forward channel that uses time-multiplexing to separate its sub-channels, the sub-channels that make up the reverse Traffic Channel are separated by Walsh codes, spreading at a fixed chip rate of 1.2288 Mcps. The exceptions to this are the Pilot and RRI Channels, which are time-multiplexed, as shown in the figure. The reverse link channels are also transmitted separately on the I- and Q-phases.

CL8300-SG.en.UL 292



Physical Layer Packets

Traffic Channel

Access Channel


FCS16 bits

6Tail bits

256-bit Packet

MAC Layer Packet234, 490, 1002,

2006,or 4074 bitsFCS

16 bits

6Tail bits

256, 512, 1024, 2048, or 4096-bitPhysical Layer Packet

User data is transmitted in physical layer packets over the air-interface. The size of a packet ranges from 256 bits to 4096 bits.

As the transmit data rate incrementally doubles from 9.6 kbps to 153.6 kbps, the MAC layer packet bit size used to construct the physical layer packet also incrementally increases from 234 to 4074, as shown in the figure. A single Frame Check Sequence (FCS) is calculated regardless of the of MAC layer packet bit size used to construct the physical layer packet. The FCS calculation results in a 16-bit CRC value which is tacked on to end of the physical layer packet just before the 6 tail bits.

The Access Channel is always transmitted at a fixed 9.6 kbps data rate. The physical layer packet for an access probe is 256 bits and consists of a 234-bit MAC layer packet, followed by a 16-bit frame sequence check (FSC) value and 6 tail bits, as shown in the figure.

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Access Channel

Frame 0 Frame 1 Frame 2 Frame 3

Transmit Power

Time

Pilot Channel

Pilot Channel

Data Channel

Preamble period Data period

• Access Channel (R-ACH)– Similar to IS-95

– Transmit access probes.

The Access Channel is used when the AT must access the system to initiate communication or respond to a direct message sent from the base station.

An access probe for IS-856 is similar to the access probe used in IS-95. The IS-856 access probe consists of a preamble followed by one or more Access Channel physical layer packets. The physical layer packet is transmitted on the Access Channel’s Data Channel.

An Access Channel physical layer packet is transmitted during a 16-slot frame, resulting in a data rate of 9.6 kbps (256 bits / 26.67 ms). The Pilot Channel is transmitted at a certain power level during the preamble. During the data portion of the access probe, the amplitude of the Data Channel is proportionate to the Pilot Channel transmit power, so that the sum of the Data and Pilot Channels transmit power is equal the Pilot Channel transmit output transmitted during the preamble period, as shown in the figure.

CL8300-SG.en.UL 294



Reverse MAC Channel and Ack Channel

• Reverse Rate Indicator (RRI) Channel– RRI symbol identifies reverse data rate

• Data Rate Control (DRC) Channel– DRC value indicates desired data rate

– DRC cover identifies the sector fromwhich the data rate has to come

• Ack Channel– Acknowledges received forward link

physical packets.

Data rate [kbps]

RRI symbol

RRI codeword

0 000 00000009.6 001 101010119.2 010 011001138.4 011 110011076.8 100 0001111

153.6 101 1011010

DRC value

Rate [kbps]

Packet length [slots]

DRC codeword

0 Null N/A 000000001 38.4 16 111111112 76.8 8 010101013 153.6 4 101010104 307.2 2 001100115 307.2 4 110011006 614.4 1 011001107 614.4 2 100110018 921.6 2 000011119 1228.8 1 11110000

10 1228.8 2 0101101011 1843.2 1 1010010112 2457.6 1 00111100

The Medium Access Control (MAC) Channel consists of two sub-channels, the Reverse Rate Indicator (RRI) Channel and the Data Rate Control (DRC) Channel.

RRI Channel

The RRI Channel is transmitted by the AT to identify for the base station in which data rate the Data Channel is transmitting. The RRI symbol (converted into a RRI codeword) indicates the data rate.

DRC Channel

The DRC Channel is sent by the AT to identify the sector with the highest carrier-to-interference (C/I) ratio and the highest rate in which the AT can receive quality data from the sector. A 4-bit DRC value, converted to a 8-bit codeword, indicates a desired data rate, and a Walsh cover, Wi

8, is used to identify to what sector in the Active Set the DRC Channel is pointed.

To maximize the overall sector throughput, IS-856 systems use a scheduling algorithm that takes advantage of a multi-user pool requesting resources from the forward link. Based on the DRC reported by each AT, the scheduling algorithm will schedule data transfer with only those ATsoperating in favorable RF conditions, so that the data is transferred at the highest possible rate.ATs operating in less favorable RF conditions are served later, hopefully when their RF conditions improve.

Ack Channel

The Ack Channel is generated to acknowledge the validity of only those forward link physical packets that are proceeded by a preamble addressing the AT. If an associated preamble is not detected, the Ack Channel is gated off.

CL8300-SG.en.UL 295




ComplexMultiplier

Pilot/RRI

Ack Σ

Σ

BasebandFilterand

QuadratureMixer

LCG LCM

I’

Q’Q

I

PNI PNQ

To RF modulation



DRC

Data

The figure shows a simplified implementation of the reverse link transmit processing and its use of the various codes.

When transmitting a Traffic Channel, five reverse sub-channels are generated: Pilot Channel and RRI Channel, Ack Channel, DRC Channel, and Data Channel. The Pilot, RRI, and Ack Channels are transmitted on the in-phase (I) component of the signal, and the DRC and Data Channels are transmitted on the quadrature-phase (Q) component of the signal.

The I- and Q-phases are transformed by the complex multiplier by multiplying the I and Q inputs by the output of the long code generator through the long code mask, the I-phase PN sequence (PNI), and the Q-phase PN sequence (PNQ).

The transformed I and Q streams are shaped and converted to the appropriate RF frequencies by the baseband filter and quadrature mixer. The output is then sent to further amplification and transmission on the reverse link.

Each component will be discussed in greater detail.

Note: When transmitting the Access Channel, only a Pilot Channel and a Data Channel is transmitted. The Pilot Channel is transmitted on the I-phase, and the Data Channel is transmitted on the Q-phase.

CL8300-SG.en.UL 296



Reverse Link Channel Coding – I-phase


3-bit RRI symbolconverted to codeword

1-bit ACK symbol

7 : 1TDM

Σ

Codewordrepeater/truncation

W0 = (++++++++++++++++)16

W4 = (++++ )8

XI

On the reverse Traffic Channel the Pilot Channel, Reverse Rate Indicator (RRI) Channel, and Ack Channel are transmitted on the in-phase component of the signal.

Pilot Channel and RRI Channel

The Pilot Channel, which is all "0" bits, is time division-multiplexed (TDM) with a 256-bit value representing the Reverse Rate Indicator (RRI) value. The actual RRI value is a 3-bit symbol identifying the reverse data rates. To provide for the 256-chip spreading of this value, the 3-bit RRI symbol is converted to one of five 7-bit values, which is repeated 37 times to generate a 259-bit pattern. The last three bits of this bit pattern are punctured (truncated) to keep a 256-bit pattern.

The 256-bit pattern is selected by the 7:1 TDM at the start of each slot clock period. At the end of the first 256-bit period, the 7:1 TDM selects all "0" bits (1793 bits) from the Pilot Channel until the end of the slot clock period. The Pilot/RRI multiplexed channel is then spread by Walsh function W0

16 and summed up with the Ack Channel.

Ack Channel

The Ack Channel consists of a 1024-chip burst transmitted during the first half of the third slot following the slot with data received from the base station. The Ack Channel is generated to acknowledge (ACK), or not acknowledge (NAK), the validity of only those data packets that are proceeded by a preamble directed to the AT. If an associated preamble is not detected, the AckChannel is gated off.

In order to cover the 1024-chip burst half-slot period, the one-bit ACK/NAK signal is first repeated 128 times by the x128 repeater, producing a 128-bit pulse burst. The pulse burst is then spread by Walsh function W4

8 prior to being scaled by the Ack Channel gain control. The output of the Ack Channel gain control is then summed with the Pilot/RRI Channel data to provide the in-phase component sent to quadrature spreading.

CL8300-SG.en.UL 297



Reverse Link Channel Coding – Q-phase

4-bit DRC symbolconverted to 8-bit codeword

3-bit DRCcover symbol

Data Channel

W2= (++ )

ΣDRC

codewordrepeater

Sectoridentifier

Turboencoder/

interleaver

W 8 = (++++++++ )16

W8i

Interleavedpacket

repeater

XQ

On the quadrature-phase of the signal for the Reverse Traffic Channel, the Data Rate Control (DRC) Channel and the Data Channel are transmitted.

DRC Channel

The DRC Channel consists of a DRC symbol, or value, that is covered by a DRC cover. The DRC value indicates the desired data rate on the Forward Traffic Channel. The 3-bit DRV cover indicates what sector in the Active Set the DRC value is intended for. In other words, the DRC cover indicates from which sector the AT wishes to receive Forward Traffic Channel.

The 4-bit DRC value is converted to an 8-bit DRC code word. The 8-bit DRC code word is repeated twice by the DRC code word repeater to produce a 16-bit symbol that is spread by Walsh function Wi

8, where i is a value between 0 and 7 selected by the 3-bit DRC cover symbol at the input of the sector identifier. As a result, the 16-bit symbol is spread to a 128-bit chip sequence.

In order to cover a 2048-chip time slot, the 128-chip sequence is further spread to a 2048-chip sequence by Walsh function W8

16. The amplitude of the resulting chip sequence is scaled via theDRC Channel gain control and summed up with the Data Channel.

Data Channel

A data packet on the reverse link is first encoded using the turbo coder, and the bit interleaved. The symbols from the interleaver are spread by Walsh function W2

4 and adjusted to a specific gain. The output of the Data Channel gain control is then summed with the DRC Channel to provide the quadrature-phase component sent to quadrature spreading.

Note: The tail bits needed to clear the encoder’s registers are embedded in the physical layer packet.

CL8300-SG.en.UL 298



Reverse Link Coding Parameters

Characteristics 9.6 19.2 38.4 76.8 153.6RRI symbol 001 010 011 100 101Bits/packet 256 512 1024 2048 4096Digital modulation BPSK BPSK BPSK BPSK BPSKCode rate 1/4 1/4 1/4 1/4 1/2PN chips/bit 128 64 32 16 8

Data rate [kbps]Characteristics 9.6 19.2 38.4 76.8 153.6RRI symbol 001 010 011 100 101Bits/packet 256 512 1024 2048 4096Digital modulation BPSK BPSK BPSK BPSK BPSKCode rate 1/4 1/4 1/4 1/4 1/2PN chips/bit 128 64 32 16 8

Data rate [kbps]

The different data rates available in IS-856 are achieved by varying the number of bits per physical layer packet, as shown in the table. Each data rate is also associated with a particular RRI symbol that is transmitted on the RRI Channel to let the base station receiver know the data rate of the packet. The digital modulation performed is BPSK.

CL8300-SG.en.UL 299



HPSK Quadrature Mixer


Σ

xxBaseband

Filter

BasebandFilter

PNI

PNQ

sin(2πfct)

cos(2πfct)

I

Q

s(t)

Σ

Σ

+

+

+

+

+

-

x

x

x

x

Decimatorby factor

of 2

xx

x

W12

Effective longcode, Q-phase

Effective longcode, I-phase

XI

XQ

After the channels have undergone necessary signal processing (encoding, symbol repetition, relative gain, etc.), the Pilot, RRI, and Ack Channel are summed together to generate the in-phase component (I) of the transmitted signal. In a similar manner, the DRC Channel and Data Channel are summed together to form the quadrature-phase component (Q). Because of different bit rates and relative gains of the channels transmitted, an imbalance occurs between I-phase and Q-phase.

Complex Scrambling

To compensate for this imbalance, complex scrambling is used during spreading, where the I and Q components are cross-multiplied with the I and Q components of the PN code. The product is a complex number, having a real and an imaginary part that are 90 degrees apart:

(I + jQ) x (PNI’ + jPNQ’) = (I x PNI’ – Q x PNQ’) + j (Q x PNI’ + I x PNQ’)

The multiplication is the same multiplication done on the forward link. However, the PN codes used, PNI’ and PNQ’, are further manipulated to generate a digital modulation technique called Hybrid Phase Shift Keying (HPSK).

The RF modulation performed with a quadrature mixer.

CL8300-SG.en.UL 300



HPSK

Σ

xxBaseband

Filter

BasebandFilter

PNI

PNQ

sin(2πfct)

cos(2πfct)

I

Q

s(t)

Σ

Σ

+

+

+

+

+

-

x

x

x

x

Decimatorby factor

of 2

xx

x

W12

Effective longcode, Q-phase

Effective longcode, I-phase

XI

XQ

Complex multiplier



In order to maximize the battery life for an AT, the AT’s amplifier must be efficient. For the amplifier to be efficient, the peak-to-average (P/A) power ratio of the signal should be as small as possible.

In IS-95, where Offset Quadrature Phase Shift Keying (OQPSK) is used, the P/A is reduced by avoiding zero-crossings in the constellation (see Digital Modulation in the CDMA Codes lesson). However, in IS-856 (and IS-2000) where multiple channels with different power levels are transmitted are transmitted on the I- and Q-phases, OQPSK is not suitable. Instead, a new digital modulation technique is introduced to reduce the zero-crossings and the P/A ratio. The modulation technique is called Hybrid Phase Shift Keying (HPSK), or Orthogonal ComplexQuadrature Phase Shift Keying (OCQPSK).

HPSK is a variation on the regular complex scrambling (see forward link) that reduces, but not eliminates, zero-crossings for the signal.

Walsh Rotator

The key component in HPSK is the so-called Walsh rotator. The Walsh rotator for the I-phase is W0

2 (+1, +1) and W12 (+1, -1) for the Q-phase. With the multiplication of these two Walsh

codes, two consecutive and identical chips are separated 90o in the final constellation, and the transition between them do not go through zero.

In order for the Walsh rotator to function properly, pairs of consecutive identical chips going into the complex scrambler are assumed. Therefore, on the reverse link, the standard specifies even-numbered Walsh codes (consists of pairs of identical bits) for the channels.

Decimator

The decimator used for the PNQ’ signal minimizes the so-called Multi-Access Interference. Decimation with a factor of two ensures that the signal holds its value for two chips, thereby randomizing the direction the signals phase rotation while keeping the 90o separation as generated by the Walsh rotator.

Reference: HPSK Spreading for 3G, Agilent Technologies, application note 1335

CL8300-SG.en.UL 301



Benefits of HPSK

Zero-crossings in the constellation increases the peak-to-average (P/A) power ratio of the signal. Signals with a high P/A ratio may saturate the amplifier, which in turn may cause out-of-band emission (interference outside the channel’s bandwidth). High P/A ratio also decreases the amplifier’s efficiency and therefore reduces battery life. The goal for modulation is to reduce the P/A ratio.

For a regular QPSK signal, the probability of zero-crossings for two signals with the same amplitude is 1/4. Since HPSK limits the zero-crossing to every other chip, the probability of zero-crossings is reduced to 1/8. By using other tricks, such as reducing the number of 0o phase shifts, the P/A ratio when using HPSK is reduced by up to 1.5 dB.

Reduction of the P/A ratio and more efficient amplifiers lead to a reduction of the out-of-band transmissions by almost 4 dB. This effect of HPSK modulation on reducing out-of-band transmissions is illustrated in the figure, and shows a 5-MHz bandwidth using a spectrum analyzer.

HPSK modulation is important at network bordering cells to reduce inter-network interference and better meet the legal requirements set in the host country.

CL8300-SG.en.UL 302



Access Channel Coding


I

QTurboencoder

W0 = (++++++++++++++++)16

W2 = (++ )4

Channel interleaver

Interleavepacket

repeater

Access CannelPacket Data

HPSK

Access Channelrelative gain

control

The Access Channel consists of a Data Channel and a Pilot Channel.

Data Channel

The physical layer packet on the Access Channel is encoded by a turbo encoder at 1/4-code rate, producing a 1024-bit symbol. The encoded packet is interleaved and repeated eight times, generating a symbol rate of 307.2 ksps.

Next, the symbols are spread by Walsh function W24, and adjusted to a specific gain. The output

of the Data Channel gain control provides the quadrature-phase of the signal that is sent to quadrature spreading.

Pilot Channel

Similar to the Pilot Channel for the Traffic Channel, the Pilot Channel for the Access Channel also contains unmodulated symbols having a binary ‘0’ bit value. The Pilot Channel is continuously transmitted using Walsh function W0

16.

Quadrature Spreading

Quadrature spreading is performed in the same manner as for the Reverse Traffic Channel; I.e., using HPSK and quadrature mixer in the RF domain.

CL8300-SG.en.UL 303




• Long Code• Walsh Code• Short Code

– Zero offset for quadrature spreading

– Same as IS-95.

For the reverse link in IS-856, the long code and short code are used in a similar manner as in IS-95.

The Walsh codes are used in IS-856 to give identities to the channels transmitted on the reverse link. In IS-95 the Walsh codes were used to perform 64-ary modulation on the reverse link. 64-ary modulation is not needed in IS-856.

Also, the long code generator is reset (registers loaded with specific values) at the start of every short code. Hence, the long code used on the reverse link is periodic with a period of 215 chips.

CL8300-SG.en.UL 304




1111111111 Permuted ATI

41 … 32 31 0…

LCMI

LCM Long code maskATI Access Terminal identifierLCM Long code maskATI Access Terminal identifier

1111111111 Permuted (ATI)’

41 … 32 31 0…

LCMQ

Traffic Channel

… 32 31 …

01

41 40 39 0

AccCycleNum Permuted (ColorCode | SectorID[23:0])

… 32 31 …

01

41 40 39 0

(AccCycleNum)’ Permuted (ColorCode | SectorID[23:0])’

LCMI

LCMQ

Access Channel

For certain channels, the long code is used to scramble and give and identity to the channel. An effective long code is generated by combining the output of the long code mask with the output of the long code generator.


LCMI and LCMQ

The in-phase component (I) and quadrature-phase component (Q) of the channels have their own long code masks, LCMI and LCMQ, respectively. LCMQ is generated by shifting the bits in LCMI one step to the left and calculate a checksum for bit 0 in LCMQ. See the standard specification for more details.

Access Channel

The long code mask used on the Access Channel is derived from the Access Channel cycle (AccCycleNum), the sector’s color code (ColorCode), and the 24 least significant bits of the sector’s ID (SectorID[23:0]). The ColorCode and SectorID[23:0] is used in a permuted fashion. See the standard specification for more details.

Traffic Channel

The long code mask for the Traffic Channel is user-specific and based on the ATI of the AT. For the user-specific long code mask a permuted version of the ATI is used.

For example, if the ATI of the AT has 32 bits:

x31 x30 x29 x28 … x1 x0

Then the permuted ATI used for the long code mask would look like:

x0 x31 x22 x13 … x18 x9

Long Code Generator

Long CodeMask

ScramblingSequence

CL8300-SG.en.UL 305



Reverse Link Walsh Codes

Walsh function Used for Phase

W016 Pilot Channel I

W48 Ack Channel I

W24 Data Channel Q

W816 DRC Channel Q

Wi8 DRC cover -

The reverse link channels are distinguished by a separate Walsh code, or functions, within the AT, as seen in the table. The Walsh codes are used to insure orthogonality. Spectrum spreading is done with the long code, which is used to distinguish between ATs as in IS-95.

Walsh codes are also used for the DRC cover symbols indicating desired forward link sector. The DRC cover Walsh codes are not used for channel orthogonality.

Remember that for HPSK to properly work, the Walsh codes must be even-numbered. Even numbered Walsh codes contain pairs of identical bits.

CL8300-SG.en.UL 306







42 bit mask (LCMI, LCMQ) identifies user

Walsh functions are used to generate MACIndex

PN Long Codes

242 - 1 bits



215 bits

Not used. A 17-tapcode is used forscrambling

64 chip offsets used to identify antenna face to the AT

4 - 64 bits



PN Long Code

The long code gets its name from the fact that it takes about 41.4 days for the code to repeat itself. On the forward link, the long code is not used. Instead, a 17-tap linear feedback shift-register is used to generate the scrambling code.

For the reverse link, the long code and the long code mask is used to identify the signal from a specific user. A permuted long code mask is used for the quadrature-phase.

PN Short Code

One of the codes used in conjunction with the Walsh code is the PN (pseudo-random noise) short code. The PN short code on the forward link is used to provide the base station with a unique identification that the AT uses to identify the serving base station.


Walsh Function


For the forward link, the Walsh functions are mapped to a specific MACIndex.


CL8300-SG.en.UL 307



Outline - 4/4





– Power control

– Pole point.

CL8300-SG.en.UL 308



8.8 Handoff Specifics – IS-856

• Reverse link– Handoffs are handled in a similar way to IS-95

– RLP selects the best frames

• Forward link– No soft handoff

– Only one user receives the forward link at any time– DRC Channel decides from what sector in the Active Set the

forward link should be transmitted• AT points the DRC Channel to different sectors based on received

C/I• This is called virtual soft handoff.

IS-856 uses the soft handoff algorithms with dynamic thresholds introduced in IS-95B. The Radio Link Protocol (RLP) is responsible for selecting the best frames coming from the sectors in the Active Set.

On the forward link, there is no soft handoff for IS-856. The forward link channels are time-multiplexed and only one AT receives the forward link at any instant of time. An AT points its DRC Channel, based on C/I, to the sector in the Active Set from which it wants to receive the Forward Traffic Channel. This procedure is called virtual soft handoff. A scheduling algorithm in the system determines what AT will receive the forward link.

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8.9 Power Control Specifics – IS-856

• Reverse link power control (RPC)– Similar to IS-95

• RPC closed loop– Base station measure Reverse Pilot Channel

• Aided by the RRI Channel

– Measurement compared to a calculated setpoint, Power Control Threshold (PCT)

– RPC Channel send RPC bits to the AT• Max frequency of 600 Hz, depends on DRCLock Channel• AT adjust power in 1dB or 0.5dB steps.

Reverse link power control (RPC) for IS-856 is similar to the RPC for IS-95. One difference is that an IS-856 AT transmits a constant Pilot Channel. By measuring a constant channel, RPC implementation in the base station may be simplified. The fact that the AT is also transmitting the RRI Channel improves the reverse link estimation at the receiver since the receiver does not have to analyze the Data Channel to determine the data rate.

The closed loop power control consists of the inner loop and the outer loop. The outer loop power control is implementation-specific, but typically adjusts the closed loop power control threshold (PCT) in the base station in order to maintain a desired quality on the Data Channel.

The inner loop power control consists of a fast feedback loop from the base station to the AT. The inner loop adjusts the transmit power of the AT by transmitting power control bits, or RPC bits on the RPC Channel. The RPC bits are transmitted with a frequency of up to 600 Hz, depending on the DRCLock Channel frequency. The RPC Channel is transmitted whenever the DRCLock Channel is not. The AT can adjust its power based on the RPC bits in steps of 1 dB or 0.5 dB.

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8.10 - Pole Point Specifics – IS-856

• Additional reverse link channel impact the pole point– Main concept remains the same.

loading*1NE

1*

11

*10'*101

1M

0b10Gain_Traffic

10Gain_DRCair

+

β+α++=

Legend:α Activity factor β Interference geometryd Chip energy over noise N0 Thermal noise

Legend:α Activity factor β Interference geometryd Chip energy over noise N0 Thermal noise

The Pilot, RRI, and DRC Channels on the reverse link are transmitted continuously while the AT is not in the dormant state. This is true regardless of how little data the AT has to send. Therefore, the pole point derivation for IS-856 is a hybrid between the approach taken for typical CDMA voice and data. The resulting expression is shown.

Note that the regular activity factor is now an expression based on the gain of the DRC Channel (DRC_Gain) and the gain of the Traffic Channel (Traffic_Gain). The Ack Channel is ignored since it is only transmitted when the AT received the Forward Traffic Channel, and there is only one AT receiving the Forward Traffic Channel at any time.

The full derivation of the pole point expression is found in the RF Engineering Guidelines.

CL8300-SG.en.UL 311



Summary

• IS-856 is a data-only technology– 2,457.6 kbps on the forward link

– 153.6 kbps on the reverse link

• Mobile stations are called access terminals• Forward link

– Time-multiplexed• Only one users receives the Traffic Channel at any time

– MACIndex indentifies user

– Complex scrambling

• Reverse link– Similar to IS-2000

– DRC Channel determines desired forward data rate and sector– HPSK used for more cost-effective amplifier.

IS-856 is an evolution of IS-2000, and a data-only technology. The reverse link is similar to the IS-2000 reverse link, and supports a data rate of 153.6 kbps. On the forward link, the channels are time-multiplexed. This means that only one user at any time receives the forward Traffic Channel. The maximum data rate on the forward link is 2,457.6 kbps.

In IS-856, an access terminal (AT) is the equivalent of a mobile station.

Forward Link

Four channels are time-multiplexed on the forward link, Pilot, MAC, Traffic, and Control Channels. Even if time-multiplexing is done, the channels are still spread using CDMA techniques.

The Walsh codes are mapped into MACIndices, and identifies users and channels.

To balance the load between the I-phase and the Q-phase, complex scrambling (multiplication) is performed at the same time as the quadrature spreading. The modulation method depends on the current data rate of the Traffic Channel. The modulation method can be QPSK, 8-PSK, or 16-QAM.

Reverse Link

The reverse link is similar the IS-2000 reverse link, with a reverse Pilot Channel and Traffic Channel similar to the IS-2000 Supplemental Channel. The R-PICH is the predominant factor in keeping the reverse link interference low.

In addition to the Pilot and Traffic Channels, the reverse link also has a DRC Channel and an Ack Channel. The DRC Channel determines from what sector the AT would receive the forward Traffic Channel, and its desired data rate. The Ack Channel acknowledges forward link packets.

In addition to complex scrambling, a Walsh rotator is introduced, and together they form a modulation technique called Hybrid Phase Shift Keying (HPSK). HPSK reduces the peak-to-average ratio; therefore, the amplifier’s efficiency is also reduced.

CL8300-SG.en.UL 312



Knowledge Check

1. At any one time, only one user is actively receiving data over the forward Traffic Channel.A. True

B. False

2. Which of the following CDMA modulation schemes is not used in 1xEV-DO?A. QPSK

B. BPSK

C. 8-PSKD. 16-QAM

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3. Complete the sentence: Forward link data is transmitted in successive ________ frames, which are divided into ___________ slots in which packets of data are transmitted.A. 20-ms, eight 2.5-msB. 40-ms, sixteen 2.5-ms

C. 48.88-ms, eight 6.11-ms

D. 26.67-ms, sixteen 1.67-ms

4. Both forward and reverse channels are time-multiplexed.A. True

B. False

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5. The Data Rate Control (DRC) Channel:A. is generated by the BTS to inform the AT of the forward Traffic

Channel data rate.

B. is generated by the AT to inform the BTS of the reverse Traffic Channel data rate.

C. is generated by the AT to inform the BTS of the forward Traffic Channel data rate.

D. is generated by the BTS to inform the AT of the reverse Traffic Channel data rate.

6. The frequency of the inner loop power control is always 600Hz.A. True

B. False

CL8300-SG.en.UL 315




7. How often will the Access Terminal monitor the Control Channel when operating in the slotted mode (Sleep State)?A. 1.667 milliseconds

B. 426.67 millisecondsC. 2.5 seconds

D. 5.12 seconds

CL8300-SG.en.UL 316

CL8300-SG.en.UL 1

Appendix IAdditional Coding Information

CL8300-SG.en.UL 2

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CL8300-SG.en.UL 3



Lesson 6: Primary and Signaling Traffic – Multiplex Option 2• Multiplex Option

specifies the type offrame used– Called MuxPDU

in IS-2000

• Signaling is transmittedas blank-and-burst ordim-and-burst.

MM Mixed Mode bitFM Frame Mode bits

MM Mixed Mode bitFM Frame Mode bits Multiplex Option 2

Transmit Rate

Primary Traffic

Signaling Traffic

Secondary Traffic

[bps] MM FM [bits/frame] [bits/frame] [bits/frame]0 - 266 0 01 0n 00 124 138 (n=0) / 0 (n=1) 0 (n=0) / 138 (n=1)

14400 1 0n 01 54 208 (n=0) / 0 (n=1) 0 (n=0) / 208 (n=1)

1 0n 10 20 242 (n=0) / 0 (n=1) 0 (n=0) / 242 (n=1)

1 0n 11 0 262 (n=0) / 0 (n=1) 0 (n=0) / 262 (n=1)

1 1000 20 222 200 - 124 0 01 000 54 67 0

7200 1 001 20 101 01 010 0 121 01 011 54 0 671 100 20 0 1011 101 0 0 1211 110 20 81 200 - 54 0 0

3600 1 n 0 20 32 (n=0) / 0 (n=1) 0 (n=0) / 32 (n=1)

1 n 1 0 52 (n=0) / 0 (n=1) 0 (n=0) / 52 (n=1)

1800 0 - 20 0 01 - 0 0 20

Format Bits

Transmit Rate

Primary Traffic

Signaling Traffic

Secondary Traffic

[bps] MM FM [bits/frame] [bits/frame] [bits/frame]0 - 266 0 01 0n 00 124 138 (n=0) / 0 (n=1) 0 (n=0) / 138 (n=1)

14400 1 0n 01 54 208 (n=0) / 0 (n=1) 0 (n=0) / 208 (n=1)

1 0n 10 20 242 (n=0) / 0 (n=1) 0 (n=0) / 242 (n=1)

1 0n 11 0 262 (n=0) / 0 (n=1) 0 (n=0) / 262 (n=1)

1 1000 20 222 200 - 124 0 01 000 54 67 0

7200 1 001 20 101 01 010 0 121 01 011 54 0 671 100 20 0 1011 101 0 0 1211 110 20 81 200 - 54 0 0

3600 1 n 0 20 32 (n=0) / 0 (n=1) 0 (n=0) / 32 (n=1)

1 n 1 0 52 (n=0) / 0 (n=1) 0 (n=0) / 52 (n=1)

1800 0 - 20 0 01 - 0 0 20

Format Bits

The Multiplex Option (MO) specifies how much and what type of information are transmitted in a frame. IS-95 has two MOs. MO1 supports frames for Rate Set (RS) 1, and MO2 supports frames for RS2. Shown in the table is MO2.

In IS-2000, the MO is called a MuxPDU (Multiplex Sub-layer Protocol Data Unit) of a certain type. MuxPDU Type 1 corresponds to MO1, and MuxPDU Type 2 corresponds to MO2. There are more MuxPDU types defined in IS-2000.

In a frame, bits can be used for primary traffic, secondary traffic, and signaling traffic. The allocation of bits between these traffic types are determined by a number of format bits: Mixed Mode (MM) bit and Frame Mode (FM) bits.

When the MM bit is set to ‘0’, only primary traffic is carried in the frame. The FM bits are not used when the MM bit is ‘0’. When the MM bit is set to ‘1’, signaling and/or secondary traffic can also be transmitted in the frame.

When transmitting mixed traffic types in a frame, the FM bits must be specified. The FM bits then control the allocation of bits between primary traffic, signaling, and secondary traffic. See table.

In a frame, the format bits are at the beginning of the frame, followed by the primary traffic bits (if any). The signaling and secondary bits are added last to the frame.

Blank-and-Burst vs. Dim-and-Burst

When the entire frame consists of signaling or secondary traffic, we say that the signaling/secondary traffic is transmitted as blank-and-burst; all primary traffic bits are removed.

If just some of the frame consists of signaling or secondary traffic, we say that the signaling/secondary traffic is transmitted as dim-and-burst; some primary traffic bits are removed.

CL8300-SG.en.UL 4



W

Lesson 7: F-FCH and F-SCH – RC4

Add FrameQuality

Indicator



SymbolRepetition

BlockInterleaver

SymbolPuncture

ModulationSymbol

ChannelBits



172 Bits/20n ms


1,512 Bits/20n ms3,048 Bits/20n ms6,120 Bits/20n ms


Bits16

668

12

1616161616

Data Rate(kbps)

9.6

1.52.7/n4.8/n9.6/n

19.2/n38.4/n76.8/n153.6/n307.2/n

R1/2

1/21/21/21/2

1/21/21/21/21/2

Factor1x

8x4x2x1x

1x1x1x1x1x

DeletionNone


NoneNoneNoneNoneNone

Symbols96

384384384384

7681,5363,0726,144

12,288

Rate (ksps)19.2

19.219.2 /n19.2 /n19.2 /n

38.4/n76.8/n

153.6/n307.2/n614.4/n

Analogous to the Reverse Fundamental Channel (R-FCH), the Forward Fundamental Channel (F-FCH) is similar to that of the 2G traffic channel. The figure shows an example of the F-FCH and F-SCH processing for RC4. The data rate for RC3, as seen at the input of the encoder, can be up to 9.6 kbps for the FCH, and up to 307.2 kbps for the SCH.

The channel bits (voice, data, or signaling) going in to the processing will first have a frame quality indicator attached so that the receiver can detect a bad frame. Next, tail bits are added to clear the encoder before the next frame enters the encoder. The encoder adds forward error correction bits to the bit stream. Depending on application, convolutional or turbo encoding is used. The symbols coming out from the encoder are then repeated and punctured to achieve the appropriate symbol rate for the block interleaver. The block interleaver will interleave the bit stream for more robust transmission.

The table shows the available processing parameters for F-FCH and F-SCH for RC4. While the processing steps are the same, the processing parameters for other radio configurations (e.g., RC5) are different.

CL8300-SG.en.UL 5



Lesson 7: F-CACH – R=1/4, SR1

Common AssignmentChannel Bits (32 Bits per 5 ms Frame)

BlockInterleaver

(192 Symbols)

Add 8-BitFrameQuality

Indicator

Add 8-BitEncoder

Tail


R=1/4, K=9

ChannelGain X

DecimationLong CodeGenerator

(1.2288 Mcps)

Long CodeMask forCommon

AssignmentChannel

38.4 ksps

ModulationSymbol

Data Rate 9.6 kbps

Signal Point Mapping0 → + 11 → – 1

No Message 0

Message present indicator

The F-CACH can also operate with R=1/2.

CL8300-SG.en.UL 6



Lesson 7: F-CCCH – R=1/4, SR1

X

Forward CommonControl Channel Bits

BlockInterleaver

Add 8-BitEncoder

Tail


R=1/4, K=9

ChannelGain

Long Code Generator(1.2288 Mcps)

Long Code Mask forForward Common Control Channel



184 Bits/10 ms376 Bits/10 ms184 Bits/20 ms376 Bits/20 ms760 Bits/20 ms

Data Rate (kbps)38.419.238.49.6

19.238.2

Symbols768768

1,536768

1,5363,072

Rate (ksps)153.676.8153.638.476.8153.6

Decimation

The F-CCCH can also operate with R=1/2.

CL8300-SG.en.UL 7



Lesson 7: F-BCCH – R=1/4, SR1

Broadcast Channel Bits (744 Bits per 40, 80, or

160 ms Broadcast Channel Slot)

BlockInterleaver

(3,072 Symbols)

Add 16-BitFrameQuality

Indicator

Add 8-BitEncoder

Tail


R=1/4, K=9

ChannelGain

Long CodeGenerator

(1.2288 Mcps)

Long CodeMask for

BroadcastChannel

76.8 ksps

ModulationSymbol

Data Rate


SequenceRepetition

(1.2, or 4x Factor)

19.2, 9.6, or 4.8 kbps

X

Decimation

The F-BCCH can also operate with R=1/2.

CL8300-SG.en.UL 8



Lesson 7: F-CPCCH – SR1

Symbol Repetition(1x Factor for Non-TD

2x Factor for TD)


No Symbol → 0

ChannelGainMUX

AssignedInitial

Offset 0

AssignedInitial

Offset N - 1

I ArmInput

PC Bits

Long Code Maskfor Common

Power ControlChannel

RelativeOffset

Calculation

ChannelGain


No Symbol → 0

Symbol Repetition(1x Factor for Non-TD

2x Factor for TD)MUX

AssignedInitial

Offset 0

AssignedInitial

Offset N - 1

Q ArmInput

PC Bits

Q ArmData Rate = 9.6 kbps

Q Arm Modulation Symbol9.6 ksps for Non-TD 19.2 for TD

Symbols Present Indicator

DecimatorLong CodeGenerator

(1.2288 Mcps)

I ArmData Rate = 9.6 kbps

I Arm Modulation Symbol9.6 ksps for Non-TD, 19.2 for TD

Symbols Present Indicator

XI

XQ

Update Rate800 bps400 bps200 bps

N 122448

CL8300-SG.en.UL 9



RC3

RC4

Lesson 7: F-DCCH – RC3 and RC4

Add FrameQuality

Indicator



R = 1/2, K = 9

BlockInterleaver

W

ModulationSymbol

ForwardDedicated

Control Channel Bits


172 Bits/20 ms1 to 171 Bits/20 ms

24 Bits/5 ms172 Bits/20 ms

1 to 171 Bits/20 ms

Bits1612

12 or 16

1612

12 or 16


1.05 to 9.55

9.69.6

1.05 to 9.55

Symbols192768768

96384384

Rate (ksps)38.438.438.4

19.219.219.2

R1/41/41/4

1/21/21/2

The F-DCCH will undergo similar scrambling procedure as F-FCH and F-SCH.

CL8300-SG.en.UL 10



R-EACH Header

R-EACHData &R-CCCH

Lesson 7: R-EACH and R-CCCH – SR1

C

Add FrameQuality

Indicator



K=9

BlockInterleaver

ModulationSymbol

ChannelBits


172 Bits/5 ms360 Bits/10n ms172 Bits/10n ms744 Bits/20n ms360 Bits/20n ms172 Bits/20n ms

Bits8

121612161612

Data Rate(kbps)

9.6

38.438.419.238.419.29.6

R1/4

1/41/41/41/41/41/4

Factor4x

1x1x2x1x2x4x

Symbols768

7681,5361,5363,0723,0723,072

Rate (ksps)153.6

153.6153.6153.6153.6153.6153.6

SymbolRepetition

CL8300

LUCENT TECHNOLOGIES – PROPRIETARY -1Use pursuant to Company instructions

Understanding the CDMA Air-Interfacesof IS-95, IS-2000, and IS-856

Appendix IIWeb-Based End-of-Course Assessment

Job-Aid

CL8300

-2 LUCENT TECHNOLOGIES – PROPRIETARYUse pursuant to Company instructions


Overview

Introduction

This appendix contains:

• Student Web-Based Level 2 Assessment Instructions

This section contains general instructions to follow before and after the end-of-course Level 2 Assessment. Your Instructor will cover this information before you take the as-sessment.

• Student JOB AID for Web-based L2A Test

The JOB AID takes you step-by-step through the entire process of how to access the Saba website, take the assessment, exit from the test, print your results, and, if necessary, retake the test.

• If You Do Not Pass the Assessment

If you do not pass the end-of-course assessment, read this section thoroughly and answer the questions before attempting to retake the assessment.

• Level 2 Assessment Material

This section contains an introduction to the Level 2 Assessment and information needed to complete certain questions in the assessment.

CL8300



Student Web-Based Level 2 Assessment Instructions

Introduction

This end-of-course assessment measures your learning through the use of knowledge-based questions, and/or task-related scenario questions with multiple-choice answers. Everything that appears on the test was covered in this course.

General instructions

This assessment is accessed via your student workstation, and includes multiple-choice and/or matching exercises.

• Utilize the resources available to you for the test so that you do not have to guess at the answers.

• Record all answers in the on-line test.

• For each question, choose the best alternative.

• If you change an answer, select the new choice.

• If you have any questions during the assessment, raise your hand, and your Instructor will come to your desk.

• Refer to the Student JOB AID for Web-based L2A Test for instructions to:

— access and log into Saba

— navigate to the test

— take the test

— exit from the test

— retake the test if necessary

— print your test results

CAUTION:

You have a maximum of three attempts for the assessment. The Saba score for the assess-ment is always the last attempt. You could possibly get a lower score on the second and/or third attempt, or even fail the assessment in an attempt to improve your score.

CL8300



After the test

Once you complete the assessment, you may choose to check over your answers, leave the room until the assessment period ends, or stay quietly at your desk. However, you may not interact with each other in any way.

If you wish to retake the assessment because of a failed first attempt, or to improve your score, you are advised to review the areas in which you need to improve, then retake the assessment later instead of immediately.

Refer to the Student JOB AID for Web-based L2A Test, and follow the steps under:

• Exit From the Test

• Print Your Test Results

• Retake the Test (if necessary)

If you need to leave the room before you finish the assessment, please raise your hand to notify your Instructor.

CL8300



Step

1.If the LUCENT EMPLOYEES PLEASE SIGN IN window pops up, click on Close Window.Ignore all of the security dialog boxes, or respond to them as you normally would.

2a

2b

2cIt is recommended that you make your new password the same as your Saba Username to make it easier to remember. Also, jot down your password on this Job Aid in case you want to atke the test more than one time._________________________________________________________________(password here)Once you have successfully changed your password, click Learning Catalog Home.

2d, 2e Click Completed Training from the Welcome! Your Name screen.2f Go to step 4a.

3aThe Completed Training: Your Name screen displays:

3bThe Completed Training: Your Name screen displays:

Completed Title Type Status Score Action 03/31/03 Understanding the CDMA Air-Interfaces of Class Successful IS-95, IS-2000, and IS-856

4a

4b The Course Menu screen displays: (for example)

This is where you can see at a glance how many times you have taken the test.The limit is 3 attempts.

5.This launches the test application. The next screen you will see is the title screen of the test.

6.

7.

You are returned to the Course Menu screen in Saba (Step 4 above).

Notice the status bar is updated with your test results (Completion Status-Score-Mastery Score-Time Spent-Total Attempts).

8.

9.

10.

Exit From the TestClick the RETURN button on the last screen of the test.

Click Assessment Results under General Reports on the left-hand side of the screen.

Print Your Test Results

Use the Print function from your browser tool bar to print the Course Menu screen or go to the next step to print a more detailed report.

Select Training Logistics from the Course Menu screen

Click the CL8300 L2A Test link.

Take the TestFollow the online instructions for taking the test.

Lesson Completion Status Score Mastery Score Time Spent Total AttemptsCL8300 L2A Test Not Attempted 66

Notice the status bar (Completion Status-Score-Mastery Score- Time Spent- Total Attempts):

CL8300: Understanding the CDMA Air-Interfaces of IS-95, IS-2000, and IS-856

If you are not prompted to change your password, go to step 3a.Click the My Training link.

Click on Completed Training.

Click the Launch/Join icon that appears on the right-hand side of the screen under the Action column to the right of the test title.

Should you experience technical difficluties, please contact:

If you are logging into Saba for the first time, you will be prompted immediately to select a new password.

During U. S. regular business hours (0800 -1800 EST)Telephone: 1-888-582-3688 or 1-407-767-2798

Email: [email protected]

Outside of U. S. regular business hoursTelephone: 1-630-713-5000 or

Email: [email protected]

Action

Internet Access and Saba Log InOpen your browser, type in https://www.lucent-product-training.com/SabaWeb/SabaWeb and press Enter.

From the Saba Welcome screen, log into Saba using your Student ID (from the class roster) or POST email handle (Lucent employees). The default Saba password is welcome . (You may have changed your password to something else.) Click on the Go button.

CL8300



11a11b

12a

12b&c You may need to use the horizontal scroll bar to see the Action column.

13.

14.

15.16.

17.

18.

19.20.

You must take the entire test, not just the questions you missed.Notice the status bar (Completion Status-Score-Mastery Score-time Spent-Total Attempts) changes each time you take the test.The limit is 3 attempts.

Click the CL8300 L2A Test link from the Course Menu screen (As in Step 5 above).

Retake the Test (If Needed)Select My Training (from Saba Web home page, Catalog screen).

Click the Completed Training or View Completed Training (As in Step 3 above).

Click the Launch/Join icon for this test in the Action column (As in Step 4 above).

From the Questionmark Reports screen,select Assessment Results Feedback Report.

From the list of assessments displayed, click Details for CL8300 under the Action column.

Click Print at the bottom of the Report page if you want a paper copy of this report.

Click Close at the bottom of the Report page.

Close the Questionmark Reports screen by clicking on the X in the upper right-hand corner of the window.You should be back at the Training Logistics screen. At this point, you may retake the test (by selecting My Training) or log off from Saba altogether (by selecting Log Off in the upper right-hand corner).

CL8300



If You Do Not Pass the Assessment

Introduction

If your Assessment Results Feedback Report indicates that “You have not met the passing criteria for this test”, please review the sections below.

Remember: Your Instructor cannot discuss the items on the test.

Once you have reviewed these sections and answered the questions, review your Assess-ment Results Feedback Report printout, noting the objectives where you did not meet the passing criteria, then review those sections in your Student Guide and/or documentation before you consider retaking the assessment.

Considerations

Please answer all of the questions below:

• Are you part of the Audience as indicated in the Course Description?

Y N

• Have you taken all of the Prerequisites as indicated in the Course Description?If so, how long ago? _________________________

Y N

• Do you have relevant work experience? Y N

• Did you attend 100% of the class presentation? Y N

• Did you ask questions within the scope of the course on topics of which were unclear to you?

Y N

• Did you participate in 100% of the workshops/hands-on exercises?

Y N

• Did you refer to your Student Guide, the available doc-umentation, or the system to help you with your an-swers?

Y N

CL8300



Retaking the assessment

Upon reviewing the questions in the previous section, you may be able to identify reasons indicating why you did not pass the assessment. If you decide to retake the assessment, consider the following:

• You have a maximum of three attempts for the assessment. The last attempt is the score that is recorded in Saba.

• Review your Assessment Results Feedback Report printout, noticing the objectives where you did not meet the passing criteria.

• Carefully review the section or sections in which you did not meet the passing criteria, using any resources available to you for the assessment before you retake the assess-ment. This may require that you retake the assessment after you return home.

NOTE:

You are advised NOT to retake the assessment immediately after the previous attempt.

• You must retake the entire assessment.

Conclusion

Going back to and reviewing your Student Guide and documentation will help you meet course objectives for this training. Many adult learners need some time to digest all that they have learned before taking an end-of-course assessment.

We recommend taking some additional time to review your course materials to ensure your success in meeting the criteria for this test.

G L O S S A R YG L - 1

Lucent Technologies - ProprietarySee Notice on first page

CL8300-SG.en.ULIssue 1.0, June 2003

...........................................................................................................................................................................................................................................................

Glossary

......................................................................................................................................................................................................

A AC

See Authentication Center

Access Attempt

A sequence of one or more access probe sequences on the Access Channel containing the same message. See also Access Probe and Access Probe Sequence.

Access Channel

A Reverse CDMA Channel used by mobile stations for communicating to the base station. The Access Channel is used for short signaling message exchanges such as call originations, responses to pages, and registrations. The Access Channel is a slotted random access channel. See also Access Channel Slot and Reverse Access Channel.

Access Channel Message

The information part of an access probe consisting of the message body, length field, and CRC.

Access Channel Message Capsule

Carries the Access Channel message.

Access Channel Preamble

The preamble of an access probe consisting of a sequence of all-zero frames.

Access Channel Request Message

An Access Channel message that is autonomously generated by the mobile station. See also Access Channel Response Message.

Access Channel Response Message

A message on the Access Channel generated to reply to a message received from the base station.

...........................................................................................................................................................................................................................................................




Access Channel Slot

The assigned time interval for an access probe. An Access Channel slot consists of an integer number of frames. The transmission of an access probe is performed within the boundaries of an Access Channel slot.

Access Network (AN)

[IS-856]The network equipment providing data connectivity between a packet switched data network (typically the Internet) and the access terminals. An access network is equivalent to a base station.

Access Probe

One Access Channel transmission consisting of a preamble and a message. The transmission is an integer number of frames in length and transmits one Access Channel message. See also Access Probe Sequence and Access Attempt.

Access Probe Sequence

A sequence of one or more access probes on the Access Channel. The same Access Channel message is transmitted in every access probe of an access attempt. See also Access Probe and Access Attempt.

Access Procedure

The set of rules governing an Access Attempt.

Access Protocol

See Access Procedure.

Access State

In the Access State, the mobile station (or access terminal) performs an access attempt to establish contact with the base station.

Access Terminal (AT)

[IS-856]A device providing data connectivity to a user. An access terminal may be connected to a computing device such as a laptop personal computer, or it may be a self-contained data device such as a personal digital assistant. An access terminal is equivalent to a mobile station.

Acknowledgment

A Layer 2 response by the mobile station or the base station confirming that a signaling message was received correctly.

Action Time

The time at which the action implied by a message should take effect.

...........................................................................................................................................................................................................................................................




Active Set

The set of pilots associated with the CDMA Channels containing Forward Traffic Channels assigned to a particular mobile station.

Active State

[IS-586]In the Active State, the access terminal communicates with the base station using the Traffic Channel.

Aging

A mechanism through which the mobile station maintains in its Neighbor Set the pilots that have been recently sent to it from the base station, and the pilots whose handoff drop timers have recently expired.

A-key

A secret, 64-bit pattern stored in the mobile station. It is used to generate/update the mobile station’s Shared Secret Data. The A-key is used in the mobile stationauthentication process.

Aloha Protocol

Developed by the University of Hawaii, the Aloha protocol is a simple communications scheme where the transmitter in a network sends data whenever there is data to send. When the data is received. the receiver sends an acknowledgement to the transmitter. If no acknowledgement is received by the transmitter, the data is sent again.

ATI

[IS-586]Access Terminal Identifier. See also Access Terminal.

Authentication

A procedure used by a base station to validate a mobile station’s identity.

Authentication Center (AC)

An entity that manages the authentication information related to the mobile station.

Authentication Response (AUTHR)

An 18-bit output of the authentication algorithm. It is used, for example, to validate mobile station registrations, originations, and terminations.

Autonomous Registration

A method of registration in which the mobile station registers without an explicit command from the base station.

...........................................................................................................................................................................................................................................................




......................................................................................................................................................................................................

Auxiliary Pilot Channel

[IS-2000]An unmodulated, direct-sequence spread spectrum signal transmitted continuously by a CDMA base station. An Auxiliary Pilot Channel is required for forward link spot beam and antenna beam forming applications, and provides a phase reference for coherent demodulation of those forward link CDMA Channels associated with the Auxiliary Pilot. The Auxiliary Pilot Channel can be a Common Auxiliary Pilot Channel, Dedicated Auxiliary Pilot Channel, or Auxiliary Transmit Diversity Pilot Channel.

Auxiliary Transmit Diversity Pilot Channel

A Transmit Diversity Pilot Channel associated with an Auxiliary Pilot Channel. The Auxiliary Pilot Channel and the Auxiliary Transmit Diversity Pilot Channel provide phase references for coherent demodulation of those forward link CDMA Channels associated with the Auxiliary Pilot and that employ transmit diversity.

AWGN

Additive White Gaussian Noise

B Bad Frame

A frame classified with insufficient frame quality, or, for Radio Configuration 1, a 9600 bps primary traffic only frame with bit errors. See also Good Frame.

Band Class

A set of frequency channels and a numbering scheme for these channels.

Base Station

A fixed station used for communicating with mobile stations. Depending upon the context, the term base station may refer to a cell, a sector within a cell, an MSC, or other part of the wireless system. A base station contains the functionality of BTSs and BSC. See also MSC, Access Network, and Mobile Station.

Base Station Authentication Response (AUTHBS)

An 18-bit pattern generated by the authentication algorithm. AUTHBS is used to confirm the validity of base station orders to update the Shared Secret Data.

Base Station Controller (BSC)

Controls one or more BTSs. See also Base Station.

Base Station Random Variable (RANDBS)

A 32-bit random number generated by the mobile station for authenticating base station orders to update the Shared Secret Data.

...........................................................................................................................................................................................................................................................




Base Transceiver Station (BTS)

Contains the transmit and receive functionality need to communicate with a mobile station over the air. The transmit function makes an electrical signal suitable for transmission through the air (RF modulation). The receive function picks up signals out of the air and converts them into an electrical signal (RF demodulation). See also Base Station.

Basic Access Mode

[IS-2000]A mode used on the Enhanced Access Channel where a mobile station transmits an Enhanced Access Channel preamble and Enhanced Access data in a method similar to that used on the Access Channel.

BATI

[IS-586]Broadcast Access Terminal Identifier. See Also Access Terminal.

Bit

Represents a “0” or a “1” for communicated user information. In CDMA, bits are spread over chips. See also chip.

Blank-and-Burst

The pre-emption of an entire Traffic Channel frame’s primary traffic by signaling traffic or secondary traffic. Blank-and-burst is performed on a frame-by-frame basis. See also Dim-and-Burst.

Boltzman’s Constant

Boltzman’s constant (1.38 x 10-33 Joules/Kelvin).

bps

Bits per second.

BPSK

Binary Phase Shift Keying.

Broadcast Control Channel

[IS-2000]A code channel in a Forward CDMA Channel used for transmission of control information and pages from a base station to a mobile station.

BSC

See Base Station Controller.

BTS

See Base Transceiver Station.

...........................................................................................................................................................................................................................................................




......................................................................................................................................................................................................

C Candidate Set

The set of pilots that have been received with sufficient strength by the mobile station to be successfully demodulated, but have not been placed in the Active Set by the base station. See also Active Set, Neighbor Set, and Remaining Set.

CDMA

See Code Division Multiple Access.

CDMA Carrier

A CDMA carrier is a pair of frequency bands, each has a bandwidth of 1.25 MHz or 3.69 MHz, supporting forward and reverse links. A CDMA carrier centers at a set of predefined carrier frequencies. A CDMA carrier can be reused in every sector. There are two special CDMA carriers; Primary Carrier and Secondary Carrier.

CDMA Channel

The set of channels transmitted between the base station and the mobile stations within a given CDMA frequency assignment. See also Forward CDMA Channel and Reverse CDMA Channel.

CDMA Channel Number

An 11-bit number corresponding to the center of the CDMA frequency assignment.

CDMA Frequency Assignment

A 1.23 MHz or 3.69 MHz segment of spectrum, depending on technology and configuration. The center of a CDMA frequency assignment is given by a CDMA channel number.

CDMA Preferred Set

The set of CDMA channel numbers in a CDMA system corresponding to frequency assignments that a mobile station will normally search to acquire a CDMA Pilot Channel. For CDMA cellular systems, the primary and secondary channels comprise the CDMA Preferred Set.

CE

See Channel Element.

Channel Element

The component in the base station performing most of the digital signal processing for CDMA.

Chip

Represents a "0" or a "1" for a CDMA carrier. In CDMA, chips carries spread bits. See also bit.

...........................................................................................................................................................................................................................................................




Chip Rate

Equivalent to the spreading rate of the channel. It is either 1.2288 Mcps or 3.6864 Mcps depending on technology and configuration.

Code Channel

A sub-channel of a Forward CDMA Channel or Reverse CDMA Channel. Each sub-channel uses an orthogonal Walsh function or quasi-orthogonal function.

Code Division Multiple Access

A technique for spread-spectrum multiple-access digital communications that creates channels through the use of unique code sequences.

Code Symbol

The output of an error-correcting encoder. Information bits are input to the encoder, and code symbols are output from the encoder. See Convolutional Code, and Turbo Code.

Coherent

In wireless communication, coherent refers to a known signal phase-reference at the receiver. The signal phase-reference is often provided by a Pilot Channel.

Common Assignment Channel

[IS-2000]A forward common channel used by the base station to acknowledge a mobile station accessing the Enhanced Access Channel, and in the case of Reservation Access Mode, to transmit the address of a Reverse Common Control Channel and associated Common Power Control Sub-Channel.

Common Power Control Channel

[IS-2000]A forward common channel which transmits power control bits (i.e., Common Power Control Sub-Channels) to multiple mobile stations. The Common Power Control Channel is used by mobile stations operating in the Reservation Access Mode or the Designated Access Mode.

Common Power Control Group

[IS-2000]A 1.25, 2.5, or 5 ms interval on the Common Power Control Channel which carries power control information for multiple mobile stations.

Common Power Control Sub-Channel

IS-2000]A sub-channel on the Common Power Control Channel used by the base station to control the power of a mobile station when operating in the Reservation Access Mode or the Designated Access Mode on the Reverse Common Control Channel.

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Complex Multiplication

See Complex Scrambling.

Complex Scrambling

The in-phase (I-phase) and quadrature-phase (Q-phase) are cross-multiplied with PN codes in order to balance the energy between the I-phase and Q-phase. Complex scrambling is also called PNCQPSK.

Connection Layer

[IS-856]The Connection Layer provides air-link connection establishment and maintenance services.

Continuous Transmission

A mode of operation in which Discontinuous Transmission is not permitted.

Convolutional Code

A type of error-correcting code. A code symbol can be considered as the convolution of the input data sequence with the impulse response of a generator function. See also Forward Error Correction.

CRC

See Cyclic Redundancy Code.

Cyclilc Redundancy Code

A class of linear error detecting codes which generate parity check bits by finding the remainder of a polynomial division. See also Frame Quality Indicator and Frame Check Sequence.

D Data Burst Randomizer

[IS-95, IS-2000]The function that determines which power control groups within a frame are transmitted on the Reverse Traffic Channel (or Reverse Fundamental Channel with Radio Configurations 1 and 2) when the data rate is lower than the maximum rate for the channel. The data burst randomizer determines for each mobile station, the pseudorandom position of the transmitted power control groups in the frame while guaranteeing that every modulation symbol is transmitted exactly once.

dB

dB A unit used to express a ratio using logarithms, called decibel.

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Deinterleaving

The process of un-permuting the symbols that were permuted by the interleaver. Deinterleaving is performed on received symbols prior to decoding. See also Interleaving.

Designated Access Mode

[IS-2000]A mode of operation on the Reverse Common Control Channel where the mobile station responds to requests received on the Forward Common Control Channel.

Digital Modulation

Depending on the bit-value or bit pattern, digital modulation generates certain energies in the quadrature-phase (Q-phase) and in-phase (I-phase) component of the signal. See also BPSK, QPSK, 8-PSK, 16-QAM, HPSK, OQPSK, OCQPSK, and PNCQPSK.

Dim-and-Burst

A frame in which primary traffic is multiplexed with either secondary traffic or signaling traffic. See also Blank-and-Burst.

Dipole Antenna

Usually a straight, center-fed, one-half wavelength antenna. See also Isotropic Antenna.

Direct Spread

A CDMA mode in the International Telecommunications Union IMT-2000 family of standards.

dBc The ratio (in dB) of the sideband power of a signal, measured in a given bandwidth at a given frequency offset from the center frequency of the same signal, to the total in-band power of the signal. For CDMA, the total in-band power of the signal is measured in a 1.23 MHz or 3.69 MHz bandwidth around the center frequency of the CDMA signal.

dBd A measure of the gain of an actual antenna compared to an dipole antenna.

dBi A measure of the gain of an actual antenna compared to an isotropic radiator.

dBm A measure of power expressed in terms of its ratio (in dB) to one milliwatt.

dBm/Hz A measure of power spectral density. dBm/Hz is the power in one Hertz of bandwidth, where power is expressed in units of dBm.

dBp A measure of power expressed in terms of its ratio (in dB) to the Pilot Channel.

dBW A measure of power expressed in terms of its ratio (in dB) to one Watt.

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G L O S S A R YG L - 1 0



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Discontinuous Transmission (DTX)

A mode of operation in which a base station or a mobile station switches its transmitter or a particular code channel on and off autonomously. See also Continuous Transmission.

Distance-Based Registration

An autonomous registration method in which the mobile station registers whenever it enters a cell whose distance from the cell in which the mobile station last registered exceeds a given threshold.

Doppler Effect

The change in the received frequency (or wavelength) of a wave, caused by time rate of change in the effective path length between the source and the receiver.

Doppler Shift

The degree of change in frequency (or wavelength) of a wave due to the doppler effect.

Dormant Mode

In the dormant mode the mobile has a logical connection with the network, but no air-link resources are allocated.

Downlink

See Forward Link.

DRCLock Channel

[IS-856]The portion of the Forward MAC Channel that indicates to the access terminal whether or not the access network can receive the DRC Channel sent by the access terminal.

DS

See Direct Spread.

DTMF

See Dual-Tone Multi-Frequency.

Dual-Tone Multi-Frequency (DTMF)

Signaling by the simultaneous transmission of two tones, one from a group of low frequencies and another from a group of high frequencies. Each group of frequencies consists of four frequencies.

E Eb

The energy of an information bit.

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Eb/N0

See Eb/NT.

Eb/NT

The ratio in dB of the combined received energy per bit to the effective noise power spectral density. Also called Eb/N0.

Ec

The energy of a chip.

Ec/I0The ratio in dB between the pilot energy accumulated over one PN chip period (Ec) to the total power spectral density (I0) in the received bandwidth.

Effective Isotropically Radiated Power (EIRP)

The product of the power supplied to the antenna, and the antenna gain in a direction relative to an isotropic antenna.

Effective Radiated Power (ERP)

The product of the power supplied to the antenna, and its gain relative to a half-wave dipole in a given direction.

EIB

See Erasure Indicator Bit.

8-PSK

8-ary Phase Shift Keying. 8-PSK can transmit 3 bits per chip cycle.

EIRP

See Effective Isotropically Radiated Power.

Electronic Serial Number (ESN)

A 32-bit number assigned by the mobile station manufacturer, uniquely identifying the mobile station equipment.

Encoder

The signal processing step performing forward error correction encoding.

Encoder Tail Bits

A fixed sequence of bits added to the end of a block of data to reset the encoder to a known state.

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Enhanced Access Channel

[IS-2000]A reverse channel used by the mobile for communicating to the base station. The Enhanced Access Channel operates in the Basic Access Mode or in the Reservation Access Mode. It is used for transmission of short messages, such as signaling, MAC messages, response to pages, and call originations. It can also be used to transmit moderate-sized data packets.

Enhanced Access Channel Preamble

[IS-2000]A non-data bearing portion of the Enhanced Access probe sent by the mobile station to assist the base station in initial acquisition and channel estimation.

Enhanced Access Data

[IS-2000]The data transmitted while in the Basic Access Mode on the Enhanced Access Channel, or while in the Reservation Access Mode on a Reverse Common Control Channel.

Enhanced Access Header

[IS-2000]A frame containing access origination information transmitted immediately after the Enhanced Access Channel preamble while in the Reservation Access Mode.

Enhanced Access Probe

[IS-2000]One Enhanced Access Channel transmission consisting of an Enhanced Access Channel preamble, optionally an Enhanced Access header, and optionally Enhanced Access data. See also Enhanced Access Probe Sequence.

Enhanced Access Probe Sequence

[IS-2000]A sequence of one or more Enhanced Access probes on the Enhanced Access Channel. See also Enhanced Access Probe.

Erasure Indicator Bit (EIB)

[IS-95, IS-2000]A bit used in the Radio Configuration 2 Reverse Traffic Channel frame structure to indicate an erased Forward Fundamental Channel frame and in the Radio Configurations 3, 4, 5, and 6 Reverse Power Control Sub-Channel to indicate frame erasure(s) and/or non-transmission on the Forward Fundamental Channel or Forward Dedicated Control Channel.

ERP

See Effective Radiated Power.

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ESN

See Electronic Serial Number.

F F

The noise figure of a receiver, often in units of dB.

F- (forward link channels)

[IS-2000]

FCS

See Frame Check Sequence.

FEC

See Forward Error Correction.

FER

Frame Error Rate.

Fixed Data Rate

The operation of a Traffic Channel where the data rate does not change from frame to frame. See also Variable Data Rates.

F-PICH Forward Pilot Channel

F-TDPICH Transmit Diversity Pilot Channel

F-CAPICH Common Auxiliary Pilot Channel

F-DAPICH Dedicated Auxiliary Pilot Channel

F-ATDPICH Auxiliary Transmit Diversity Pilot Channel

F-SYNC Sync Channel

F-BCCH Broadcast Control Channel

F-PCH Paging Channel

F-QPCH Quick Paging Channel

F-CPCCH Common Power Control Channel

F-CACH Common Assignment Channel

F-CCCH Forward Common Control Channel

F-DCCH Forward Dedicated Control Channel

F-FCH Forward Fundamental Channel

F-SCH Forward Supplemental Channel

F-SCCH Forward Supplemental Code Channel

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Flexible Data Rate

The operation of a Traffic Channel with Radio Configuration 3 or above, where the frame format, including the number of information bits, the number of reserved bits, and the number of frame quality indicator bits, is configurable.

Forward CDMA Channel

A CDMA Channel from a base station to mobile stations. The Forward CDMA Channel contains one or more code channels that are transmitted on a CDMA frequency assignment using a particular Pilot PN offset.

Forward Channel

[IS-856]Defined as the portion of the CDMA Channel consisting of those Physical Layer channels transmitted from the access network to the access terminal.

Forward Common Control Channel

[IS-2000]A control channel used for the transmission of digital control information from a base station to one or more mobile stations. See also Forward Dedicated Control Channel.

Forward Control Channel

[IS-856]The channel that carries data to be received by all access terminals monitoring the Forward Channel.

Forward Dedicated Control Channel

[IS-2000]A portion of a Radio Configuration 3 through 9 Forward Traffic Channel used for the transmission of higher-level data, control information, and power control information from a base station to a mobile station. See also Forward Common Control Channel.

Forward Error Correction

A process whereby data is encoded with convolutional or turbo codes to assist in error correction of the link. See also Encoder.

Forward Fundamental Channel

[IS-95]See Forward Traffic Channel.[IS-2000]A portion of a Forward Traffic Channel which carries a combination of higher-level data and power control information.See also Reverse Fundamental Channel.

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Forward Link

The communication path from base station to the mobile station. See also Reverse Link.

Forward MAC Channel

[IS-856]The portion of the Forward Channel dedicated to Medium Access Control activities. The Forward MAC Channel consists of the RPC, DRCLock, and RA Channels.

Forward MAC Reverse Activity (RA) Channel

[IS-856]The portion of the Forward MAC Channel that indicates activity level on the Reverse Channel.

Forward MAC Reverse Power Control (RPC) Channel

[IS-856]The portion of the Forward MAC Channel that controls the power of the Reverse Channel for one particular access terminal.

Forward Pilot Channel

[IS-95, IS-2000]An unmodulated, direct-sequence spread spectrum signal transmitted continuously by each CDMA base station. The Pilot Channel allows a mobile station to acquire the timing of the Forward CDMA Channel, provides a phase reference for coherent demodulation, and provides means for signal strength comparisons between base stations for determining when to handoff.[IS-856]The portion of the Forward Channel that carries the pilot.See also Reverse Pilot Channel.

Forward Power Control Sub-Channel

[IS-95, IS-2000]A sub-channel on the Forward Fundamental Channel or Forward Dedicated Control Channel used by the base station to control the power of a mobile station when operating on the Reverse Traffic Channel. See also Forward MAC Reverse Power Control Channel.

Forward Supplemental Channel

[IS-2000]A portion of a Radio Configuration 3 through 9 Forward Traffic Channel which operates in conjunction with a Forward Fundamental Channel or a Forward Dedicated Control Channel in that Forward Traffic Channel to provide higher data rate services, and on which higher-level data is transmitted.

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Forward Supplemental Code Channel

[IS-95B, IS-2000]A portion of a Radio Configuration 1 and 2 (IS-95) Forward Traffic Channel which operates in conjunction with a Forward Fundamental Channel in that Forward Traffic Channel to provide higher data rate services, and on which higher-level data is transmitted.

Forward Traffic Channel

[IS-95, IS-2000]One or more code channels used to transport user and signaling traffic from the base station to the mobile station. See Forward Fundamental Channel, Forward Dedicated Control Channel, Forward Supplemental Channel, and Forward Supplemental Code Channel.[IS-856]The portion of the Forward Channel that carries information for a specific access terminal. The Forward Traffic Channel can be used as either a dedicated resource or a non-dedicated resource. Prior to successful access terminal authentication, the Forward Traffic Channel serves as a non-dedicated resource. Only after successful access terminal authentication can the Forward Traffic Channel be used as a dedicated resource for the specific access terminal.

Fractional Preamble

[IS-2000]A preamble in a sequence sent on the Reverse Pilot Channel prior to transmitting on the Enhanced Access Channel or the Reverse Common Control Channel.

Frame

[IS-95, IS-2000]A basic timing interval in the system. Most channels can handle a frame of 20 ms. For the Sync Channel, a frame is 26.666... ms long. For the Common Assignment Channel, a frame is 5 ms long. Other frame sizes are 10, 40, and 80 ms long. See the IS-95 and IS-2000 standards specifications.[IS-856]The duration of time specified by 16 slots or 26.66... ms.

Frame Category

A classification of a received Traffic Channel frame based upon transmission data rate, the frame contents (primary traffic, secondary traffic, or signaling traffic), and whether there are detected errors in the frame.

Frame Check Sequence (FCS)

[IS-856]A CRC check applied to a Physical Layer packet.

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Frame Offset

A time skewing of Traffic Channel frames from system time in integer multiples of 1.25 ms.

Frame Quality Indicator

The CRC check applied to frames.

G Gated Transmission

A mode of operation in which the mobile station transmitter or certain channels are gated on and off during specific power control groups.

Global Positioning System (GPS)

A US government satellite system that provides location and time information to users. See Navstar GPS Space Segment / Navigation User Interfaces ICD-GPS-200 for specifications. See also System Time.

Good Frame

A frame not classified as a bad frame.

Good Message

A received message is declared a good message if it is received with a correct CRC.

GPS

See Global Positioning System.

H Half Frame

[IS-95, IS-2000]A 10 ms interval on the Paging Channel. Two half frames comprise a frame. The first half frame begins at the same time as the frame.

Handoff

The act of transferring communication with a mobile station from one base station to another. See also Soft Handoff, Softer Handoff, Semi-Soft Handoff, and Hard Handoff.

Hard Handoff

A handoff characterized by a temporary disconnection of the Traffic Channel. Hard handoffs occur when the mobile station is transferred between disjoint Active Sets, the CDMA frequency assignment changes, the frame offset changes, or the mobile station is directed from a CDMA Traffic Channel to an analog voice channel. See also Soft Handoff and Semi-Soft Handoff.

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Hash Function

A function used by the mobile station to select one out of N available resources. The hash function distributes the available resources uniformly among a random sample of mobile stations.

HLR

See Home Location Register.

Home Location Register

The location register to which a MIN is assigned for record purposes such as subscriber information.

Home System

The cellular system in which the mobile station subscribes for service.

HPSK

Hybrid Phase Shift Keying. HPSK is a variation of complex scrambling (PNCQPSK) where a Walsh rotator reduces zero-crossings in the constellation diagram for the signal.

I Idle Handoff

The act of transferring reception of the Paging Channel or Control Channel from one base station to another, when the mobile station is in the Idle State.

Idle State

In the Idle State, the mobile station (or access terminal) receives control information from the base station and is ready to communicate with the system.

Implicit Registration

A registration achieved by a successful transmission of an origination or page response on the Access Channel.

IMSI

International Mobile Subscriber Identity.

Initialization State

In the Initialization State, the mobile station (or access terminal) tunes to a CDMA carrier and initializes itself for communication with the system.

Interleaving

The process of permuting a sequence of symbols. See also Deinterleaving.

I0The total power spectral density of interference received by a mobile station.

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IP

The initial open loop power radiated by a mobile station on the first probe during the access procedure.IP also means Internet Protocol.

Isotropic Antenna

A hypothetical antenna that radiates or receives equally in all directions. Isotropic antennas do not exist physically but represent convenient reference antennas for expressing directional properties of physical antennas. See also Dipole Antenna.

K kbps

Kilo-bits per second (103 bits per record).

kHz

Kilohertz (103 Hertz).

ksps

Kilo-symbols per second (103 symbols per second).

L Layering

A method of organization for communication protocols. A layer is defined in terms of its communication protocol to a peer layer in another entity, and the services it offers to the next higher layer in its own entity.

Layer 1

See Physical Layer.

Layer 2

Layer 2 provides for the correct transmission and reception of signaling messages, including partial duplicate detection. See also Layering and Layer 3.

Layer 3

Layer 3 provides the control of the cellular telephone system. Signaling messages originate and terminate at layer 3. See also Layering and Layer 2.

Local Control

An optional mobile station feature used to perform manufacturer-specific functions.

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Long Code

A PN sequence with period 242 - 1 that is used for scrambling on the Forward CDMA Channel and spreading on the Reverse CDMA Channel. The long code uniquely identifies a mobile station on both the Reverse Traffic Channel and the Forward Traffic Channel. The long code provides limited privacy. The long code also separates multiple overhead channels of the same type (e.g., Access Channel) on the same CDMA Channel. See also Public Long Code and Private Long Code.

Long Code Mask

A 42-bit binary number that creates the unique identity of the long code. See also Public Long Code, Private Long Code, Public Long Code Mask, and Private Long Code Mask.

Long PN Code

See Long Code.

LSB

Least Significant Bit.

M MAC Layer

The Medium Access Control (MAC) layer defines the procedures used to receive and to transmit over the Physical Layer.

MATI

[IS-856]Multicast Access Terminal Identifier. See also Access Terminal.

Maximal Length Sequence (m-Sequence)

A binary sequence of period 2n-1, where n a positive integer, with no internal periodicities. A maximal length sequence can be generated by a tapped n-bit shift register with linear feedback. See also PN Code.

MC

See Multi-Carrier.

Mcps

Megachips per second (106 chips per second). See also Chip.

Mean Input Power

The total received calorimetric power measured in a specified bandwidth at the antenna connector, including all internal and external signal and noise sources.

Mean Output Power

The total transmitted calorimetric power measured in a specified bandwidth at the antenna connector when the transmitter is active.

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Message Capsule

A sequence of bits comprising a single message and padding. The padding always follows the message and may be of zero length.

Message CRC

The CRC associated with a message. See also Cyclic Redundancy Code.

Message Field

A basic named element in a message. A message field may consist of zero or more bits.

Message Record

An entry in a message consisting of one or more fields that repeats in the message.

MHz

Megahertz (106 Hertz).

MIN

See Mobile Station Identification Number.

Mobile Station

A station that communicates with the base station. See also Access Terminal.

Mobile Station Identification Number (MIN)

[IS-95, IS-2000]The 34-bit number that is a digital representation of the 10-digit directory telephone number assigned to a mobile station. See also IMSI.

Mobile Station Originated Call

A call originating from a mobile station.

Mobile Station Terminated Call

A call received by a mobile station (not to be confused with a disconnect or call release).

Mobile Switching Center (MSC)

A configuration of equipment that provides cellular radiotelephone service. Also called the Mobile Telephone Switching Office (MTSO).

Modulation Symbol

The input to the signal point mapping block, and the output of the interleaver or the symbol repetition block, if present.

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Modulo-2 Addition

Modulo-2 addition is a binary addition with no carry. Modulo-2 addition can be realized using XOR gates. See table.

ms

Millisecond (10-3 second).

MSB

Most significant bit.

MSC

See Mobile Switching Center.

MTSO

See Mobile Switching Center.

Multi-Carrier

[IS-2000]A CDMA mode in the International Telecommunications Union IMT-2000 family of standards. The mode uses N (N =1) adjacent 1.2288 Mcps direct-sequence spread RF carriers on the Forward CDMA Channel and a single direct-sequence spread RF carrier on the Reverse CDMA Channel.

Multipath

The propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths.

Multiplex Option

The ability of the multiplex sublayer and lower layers to be tailored to provide special capabilities. A multiplex option defines such characteristics as the frame format and the rate decision rules. See also Multiplex Sublayer.

Multiplex Sublayer

One of the conceptual layers of the system that multiplexes and demultiplexes primary traffic, secondary traffic, and signaling traffic. See also Multiplex Option.

A B A XOR B

0 0 0

0 1 1

1 0 1

1 1 0

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N Neighbor Set

The set of pilots associated with the CDMA Channels that are probable candidates for handoff. Normally, the Neighbor Set consists of the pilot channels associated with CDMA Channels that cover geographical areas near the mobile station. See also Active Set, Candidate Set, and Remaining Set.

Network

A network is a subset of a cellular system, such as an area-wide cellular network, a private group of base stations, or a group of base stations set up to handle a special requirement. A network can be as small or as large as needed, as long as it is fully contained within a system. See also System.

Network Identification (NID)

A number that uniquely identifies a network within a cellular system. See also System Identification.

NID

See Network Identification.

N0

The absolute minimum noise power spectral density received due to noise temperature, thermal noise, and noise figure.

Non-Autonomous Registration

A registration method in which the base station initiates registration. See also Autonomous Registration.

Non-Slotted Mode

[IS-95, IS-2000]An operation mode of the mobile station in which the mobile station continuously monitors the Paging Channel when in the Idle State.

ns

Nanosecond (10-9 second).

NT

The effective noise power spectral density.

NULL

Not having any value.

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Null Traffic Channel Data

One or more frames of a specified data sequence sent at the lowest agreed-upon rate of the negotiated Radio Configuration. Null Traffic Channel data may be sent when there is no primary, secondary, or signaling traffic available. Null Traffic Channel data serves to maintain the connectivity between the mobile station and the base station. See also Traffic Channel.

Numeric Information

Numeric information consists of parameters that appear as numeric fields in messages exchanged by the base station and the mobile station, and information used to describe the operation of the mobile station.

O OCQPSK

Orthogonal Complex Quadrature Phase Shift Keying.

Octet

A group of eight bits.

OLC

See Overload Class (CDMA).

Optional Field

A field defined within a message structure that is optionally transmitted to the message recipient.

OQPSK

Offset Quadrature Phase Shift Keying.

Order

A type of message that contains control codes for either the mobile station or the base station.

Ordered Registration

A registration method in which the base station orders the mobile station to send registration related parameters.

Origination

See Mobile Station Originated Call.

Orthogonal

Two signals are orthogonal if the correlation, the sum of products or integral, equals to zero.

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Orthogonal Modulator

[IS-95, IS-2000]A 64-ary orthogonal modulator transmits one of 64 possible, orthogonal, modulation symbols, Walsh codes, for each six code symbols.

Orthogonal Transmit Diversity (OTD)

A forward link transmission method which distributes forward link channel symbols among multiple antennas, and spreads the symbols with a unique Walsh or quasi-orthogonal function associated with each antenna.

OTD

See Orthogonal Transmit Diversity.

Overhead Message

A message sent by the base station to communicate base-station-specific and system-wide information to mobile stations.

Overload Class

The means used to control system access by mobile stations, typically in emergency or other overloaded conditions. Mobile stations are assigned one (or more) of sixteen overload classes. Access to the CDMA system can then be controlled on a per class basis by persistence values transmitted by the base station.

P Packet

The unit of information exchanged between the base station and the mobile station.

Padding

A sequence of bits used to fill from the end of a message to the end of a message capsule, typically to the end of the frame or half frame.

Paging

The act of seeking a mobile station when the mobile station needs to be contacted. See also Paging Channel.

Paging Channel (CDMA)

[IS-95, IS-2000]A code channel in a Forward CDMA Channel used for transmission of control information and pages from a base station to a mobile station. See also Paging, Broadcast Control Channel, Forward Common Control Channel, Forward Dedicated Control Channel, and Forward Control Channel.

Paging Channel Slot

An 80 ms interval on the Paging Channel. Mobile stations operating in the slotted mode are assigned specific slots in which they monitor messages from the base station.

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Parameter-Change Registration

A registration method in which the mobile station registers when certain of its stored parameters change.

Parity Check Bits

Bits added to a sequence of information bits to provide error detection, correction, or both. See also Cyclic Redundancy Code.

Persistence

A probability measure used by the mobile station to determine if it should transmit in a given Access Channel Slot or on an Enhanced Access Channel.

Physical Layer

The Physical Layer provides the channel structure, frequency, power output, modulation, and encoding specifications for the forward and reverse links. See also Layering.

Pilot Channel

An unmodulated, direct-sequence spread spectrum signal transmitted continuously by each CDMA base station. A Pilot Channel provides a phase reference for coherent demodulation and may provide a means for signal strength comparisons between base stations for determining when to handoff. See also Forward Pilot Channel and Reverse Pilot Channel.

Pilot Increment (PILOT_INC)

A value indicating useable PN offsets, in multiples of 64 PN chips. For example, if the pilot increment is 4, then every fourth PN offset can be used.

Pilot PN Sequence

A pair of modified maximal length PN sequences with period 215 used to spread the Forward CDMA Channel and the Reverse CDMA Channel. Different base stations are identified by different pilot PN sequence offsets.

Pilot PN Sequence Offset Index

Also called pilot PN offset. The PN offset in units of 64 PN chips of a Pilot Channel, relative to the zero offset pilot PN sequence.

Pilot Strength

The ratio of received Pilot Channel energy to overall received energy. See also Ec/I0.

PN

Pseudo-noise.

PN Chip

One bit in the PN sequence.

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PN Code

Pseudo-random noise, or pseudo-noise (PN), code is a maximal length sequence, usually with period 2n-1 where n is a positive number.

PNCQPSK

Pseudo-Noise Complex Quadrature Phase Shift Keying. PNCQPSK is more commonly referred to as complex scrambling.

PN Sequence

Pseudo-noise sequence. A periodic binary sequence.

Power Control Bit

A bit sent on the Forward Power Control Sub-Channel, Reverse Power Control Sub-Channel, or Common Power Control Sub-Channel to signal the mobile station or base station to increase or decrease its transmit power.

Power Control Group

A 1.25 ms interval on the Forward Traffic Channel, the Reverse Traffic Channel, and the Reverse Pilot Channel. See also Power Control Bit.

Power-Down Registration

An autonomous registration method in which the mobile station registers on power down.

Power-Up Registration

An autonomous registration method in which the mobile station registers on power up.

ppm

Parts per million.

Preamble

See Access Channel Preamble, Enhanced Access Channel preamble, Reverse Common Control Channel preamble, and Traffic Channel Preamble.

Primary Carrier

The primary CDMA carrier is the default carrier in a CDMA system where a user terminal should tune to when power-up. All CDMA systems should implement the primary carrier. See also Secondary Carrier.

Primary CDMA Channel

A CDMA Channel at a pre-assigned frequency assignment used by the mobile station for initial acquisition. See also Secondary CDMA Channel.

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Primary Cell Site

During a soft handoff, the cell site entity that has direct control of call processing. Primary cell site is virtual in nature, since both the primary cell site and the secondary cell site can actually be at the same physical cell. The primary cell site can initiate forward control messages. There is exactly one primary cell site during a soft handoff. See also Secondary Cell Site.

Primary Paging Channel (CDMA)

[IS-95, IS-2000]The default code channel (code channel 1) assigned for paging on a CDMA Channel. See also Paging Channel.

Primary Reverse Power Control Sub-Channel

[IS-2000]A Reverse Power Control Sub-Channel used to power control the Forward Dedicated Control Channel or Forward Fundamental Channel.

Primary Traffic

The main traffic stream carried between the mobile station and the base station, supporting the active primary service option, on the Traffic Channel. See also Secondary Traffic, Signaling Traffic, and Service Option.

Private Long Code

The long code characterized by the private long code mask. See also Long Code.


The long code mask used to form the private long code. See also Public Long Code Mask and Long Code.

Processing Gain

See Spreading Gain.

PSTN

Public switched telephone network.

Public Long Code

The long code characterized by the public long code mask. See also Long Code.

Public Long Code Mask

The long code mask used to form the public long code. The mask contains a permutation of the bits of the mobile station’s ESN, the TMSI, or the particular mask specified by the base station. The mask also includes the channel number when used for a Supplemental Code Channel. See also Private Long Code Mask and Long Code.

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Punctured Code

An error-correcting code generated from another error-correcting code by deleting (i.e., puncturing) code symbols from the coder output. See also Forward Error Correction.

Q QIB

See Quality Indicator Bit.

QPSK

Quadrature Phase Shift Keying. QPSK can transmit 2 bits per chip cycle.

Quadrature Mixer

The RF modulation of two carrier components, which are 90 degrees apart in phase.

Quality Indicator Bit

[IS-2000]A bit used in the Radio Configurations 3, 4, 5, and 6 Reverse Power Control Sub-Channel to indicate signal quality on the Forward Dedicated Control Channel. When the Forward Fundamental Channel is present, this bit is set the same as the Erasure Indicator Bits.

Quasi-Orthogonal Function

A function created by applying a quasi-orthogonal masking function to an orthogonal Walsh function. See also Walsh Function.

Quick Paging Channel

[IS-2000]An uncoded, spread, and On-Off-Keying (OOK) modulated spread spectrum signal sent by a base station to inform mobile stations, operating in the slotted mode during the Idle State, whether to receive the Forward Common Control Channel or the Paging Channel starting in the next Forward Common Control Channel or Paging Channel frame.

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R R- (reverse link channels)

[IS-2000]

Radio Access Network (RAN)

The system comprised of user devices (mobile stations and access terminals), base stations, and MSC equipment.

Radio Configuration

[IS-2000]A set of Forward Traffic Channel and Reverse Traffic Channel transmission formats that are characterized by Physical Layer parameters such as data rates, modulation characteristics, and spreading rate.

Rake Receiver

A technique where multiple baseband correlators (“fingers”) individually process several received multipath components. The output from the fingers are then combined to a single signal.

RAN

See Radio Access Network.

Rate Set

[IS-95]Specifies the data rates used for a Traffic Channel. See also Radio Configuration.

RATI

[IS-856]Random Access Terminal Identifier. See also Access Terminal.

Rayleigh Fading

The phase-interference fading caused by mutlipath, and which may be approximated by the Rayleigh distribution.

R-PICH Reverse Pilot Channel

R-ACH Access Channel

R-EACH Enhanced Access Channel

R-CCCH Reverse Common Control Channel

R-DCCH Reverse Dedicated Control Channel

R-FCH Reverse Fundamental Channel

R-SCH Reverse Supplemental Channel

R-SCCH Reverse Supplemental Code Channel

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RC

See Radio Configuration.

Registration

The process by which a mobile station identifies its location and parameters to a base station. See also Autonomous Registration.

Registration Zone

A collection of one or more base stations treated as a unit when determining whether a mobile station should perform zone-based registration.

Release

A process that the mobile station and base station use to inform each other of call disconnect.

Remaining Set

The set of all allowable pilot offsets as determined by PILOT_INC, excluding the pilot offsets of the pilots in the Active Set, Candidate Set, and Neighbor Set. See also Active Set, Candidate Set, and Neighbor Set.

Request

A layer 3 message generated by either the mobile station or the base station to retrieve information, ask for service, or command an action. See also Response.


A mode used on the Enhanced Access Channel and Reverse Common Control Channel where a mobile station transmits an Enhanced Access Channel preamble and an Enhanced Access header in the Enhanced Access probe. The Enhanced Access data is transmitted on a Reverse Common Control Channel using closed loop power control.

Response

A layer 3 message generated as a result of another message, typically a request. See also Request.

Reverse Access Channel

[IS-856]The portion of the Reverse Channel that is used by access terminals to communicate with the access network when they do not have a Traffic Channel assigned. There is a separate Reverse Access Channel for each sector of the access network. See also Access Channel.

Reverse Access Data Channel

[IS-856]The portion of the Reverse Access Channel that carries data. See also Access Channel Message.

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Reverse Access Pilot Channel

[IS-856]The portion of the Reverse Access Channel that carries the pilot.

Reverse CDMA Channel

The CDMA Channel from the mobile station to the base station. From the base station's perspective, the Reverse CDMA Channel is the sum of all mobile station transmissions on a CDMA frequency assignment.

Reverse Channel

[IS-856]The portion of the CDMA Channel consisting of those Physical Layer channels transmitted from the access terminal to the access network.

Reverse Common Control Channel

[IS-2000]A portion of a Reverse CDMA Channel used for the transmission of digital control information from one or more mobile stations to a base station. The Reverse Common Control Channel can operate in a Reservation Access mode or Designated Access mode. The channel is power controlled in both modes, and may support soft handoff in the Reservation Access Mode.

Reverse Common Control Channel Preamble

[IS-2000]A non-data bearing portion of the Reverse Common Control Channel sent by the mobile station to assist the base station in initial acquisition and channel estimation.

Reverese Dedicated Control Channel

[IS-2000]A portion of a Radio Configuration 3 through 6 Reverse Traffic Channel used for the transmission of higher-level data and control information from a mobile station to a base station.

Reverse Fundamental Channel

[IS-95]See Reverse Traffic Channel.[IS-2000]A portion of a Reverse Traffic Channel which carries higher-level data and control information from a mobile station to a base station.See also Forward Fundamental Channel.

Reverse Link

The communication path from the mobile station to the base station. See also Forward Link.

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Reverse Pilot Channel

[IS-2000, IS-856]An unmodulated, direct-sequence spread spectrum signal transmitted continuously by a CDMA mobile station. A Reverse Pilot Channel provides a phase reference for coherent demodulation and may provide a means for signal strength measurement. See also Forward Pilot Channel and Reverse Traffic Pilot Channel.

Reverse Power Control Sub-Channel

[IS-95, IS-2000]A sub-channel on the Reverse Pilot Channel used by the mobile station to control the power of a base station when operating on the Forward Traffic Channel with Radio Configuration 3 through 9.

Reverse Supplemental Channel

[IS-2000]A portion of a Radio Configuration 3 through 6 Reverse Traffic Channel which operates in conjunction with the Reverse Fundamental Channel or the Reverse Dedicated Control Channel in that Reverse Traffic Channel to provide higher data rate services, and on which higher-level data is transmitted.

Reverse Supplemental Code Channel

[IS95B, IS-2000]A portion of a Radio Configuration 1 and 2 Reverse Traffic Channel which operates in conjunction with the Reverse Fundamental Channel in that Reverse Traffic Channel, and (optionally) with other Reverse Supplemental Code Channels to provide higher data rate services, and on which higher-level data is transmitted.

Reverse Supplemental Code Channel Preamble

[IS-95B, IS-2000]A sequence of all-zero frames that is sent by the mobile station on the Reverse Supplemental Code Channel as an aid to Traffic Channel acquisition.

Reverse Traffic Ack Channel

[IS-856]The portion of the Reverse Traffic Channel that indicates the success or failure of the Forward Traffic Channel reception.

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Reverse Traffic Channel

[IS-95, IS-2000]A Reverse CDMA Channel used to transport user and signaling traffic from a single mobile station to one or more base stations.[IS-856]The portion of the Reverse Channel that carries information from a specific access terminal to the access network. The Reverse Traffic Channel can be used as either a dedicated resource or a non-dedicated resource. Prior to successful access terminal authentication, the Reverse Traffic Channel serves as a non-dedicated resource. Only after successful access terminal authentication can the Reverse Traffic Channel be used as a dedicated resource for the specific access terminal.

Reverse Traffic Channel Preamble

[IS-95]A sequence of all-zero frames that is sent by the mobile station on the Reverse Traffic Channel. The preamble is sent during initialization of the Traffic Channel.[IS-2000]A non-data bearing portion of the Reverse Pilot Channel sent by the mobile station to aid the base station in initial acquisition and channel estimation for the Reverse Dedicated Control Channel and Reverse Fundamental Channel.

Reverse Traffic Data Channel

[IS-856]The portion of the Reverse Traffic Channel that carries user data.

Reverse Traffic MAC Channel

[IS-856]The portion of the Reverse Traffic Channel dedicated to Medium Access Control (MAC) activities. The Reverse Traffic MAC Channel consists of the RRI and DRC Channels. See also MAC Layer.

Reverse Traffic MAC Data Rate Control (DRC) Channel

[IS-856]The portion of the Reverse Traffic Channel that indicates the rate at which the access terminal can receive the Forward Traffic Channel, and the sector from which the access terminal wishes to receive the Forward Traffic Channel.

Reverse Traffic MAC Reverse Rate Indicator (RRI) Channel

[IS-856]The portion of the Reverse Traffic Channel that indicates the rate of the Reverse Traffic Data Channel.

Reverse Traffic Pilot Channel

[IS-856]The portion of the Reverse Traffic Channel that carries the pilot. See also Reverse Pilot Channel.

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RF Carrier

A direct-sequence spread RF channel. For the Forward CDMA Channel, the number of RF carriers is equal to the Spreading Rate; for the Reverse CDMA Channel, there is one RF carrier.

RLP

Radio Link Protocol provides retransmission and duplicate detection for an octet-aligned data stream.

RN

Random Number. See also Access Procedure.

Roamer

A mobile station operating in a cellular system (or network) other than the one from which service was subscribed.

RP

The random time associated with the persistence of the mobile station during the access procedure.

RS

The random time associated with the sequence repetition of the mobile station during the access procedure.

RT

The random time associated with the delay before transmitting again of the mobile station during the access procedure.

Rx

Receive.

S Scrambling

When two signals, b(t) and c(t), have the same rate, the product y(t)=b(t)c(t) contains all the information of b(t) and has the same rate. The spectrum of the signal is unchanged, and the incoming bit stream is said to be encrypted or scrambled. In other words, b(t) is made unintelligible at a receiver not equipped with an appropriately set descrambling device. See also Spreading.

Search Window

The range of PN chips that a receiver searches for a signal. A mobile station receiver searches for the Forward Link Pilot. A base station receiver searches for the Reverse Pilot Channel or the Reverse Traffic Channel.

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Secondary Carrier

Similar to the primary carrier. If a CDMA system has two or more carriers, then it should also implement the secondary carrier. If a user terminal can not find the primary carrier, it should tune to the secondary carrier.

Secondary CDMA Channel

A pre-assigned channel in a CDMA cellular system for Spreading Rate 1 (IS-95 operation) used by the mobile station for initial acquisition. See also Primary CDMA Channel.

Secondary Cell Site

During a soft handoff, the cell site that does not have direct control of call processing. See also Primary Cell Site.

Secondary Reverse Power Control Sub-Channel

A Reverse Power Control Sub-Channel used to control a Forward Supplemental Channel.

Secondary Traffic

An additional traffic stream that can be carried between the mobile station and the base station on the Traffic Channel. See also Primary Traffic and Signaling Traffic.

Sector

dThe part of the radio access network that provides one CDMA Channel.

Security Layer

[IS-856]The Security Layer provides authentication and encryption services. See also Layering.

Semi-Soft Handoff

A handoff which does not require a new assignment of the frame selecting entity at the MSC. See also Soft Handoff and Hard Handoff.

Service Option

A service capability of the system. Service options may be applications such as voice, data, or facsimile.

Serving Frequency

The CDMA frequency on which a mobile station is currently communicating with one or more base stations.

Session Layer

[IS-856]The Session Layer provides protocol negotiation, protocol configuration, and state maintenance services. See also Layering.

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Shared Secret Data (SSD)

A 128-bit pattern stored in the mobile station (in semi-permanent memory) and known by the base station. SSD is a concatenation of two 64-bit subsets: SSD_A, which is used to support the authentication procedures, and SSD_B, which serves as one of the inputs to the process generating the encryption mask and private long code. See also Authentication.

Short PN Code

The short PN code is also called sector-specific PN code or pilot PN code. It is a modified PN code with period 215. A sector is identified by a pair of short PN codes. See also Pilot PN Sequence and Pilot PN Sequence Offset Index.

SID

See System Identification.

Signaling Traffic

Control messages that are carried between the mobile station and the base station on the Traffic Channel. See also Primary Traffic and Secondary Traffic.

16-QAM

16-ary Quadrature Phase Shift/Amplitude Modulation. 16-QAM can transmit 4 bits per chip cycle.

64-ary Modulation

See Orthogonal Modulator.

Slot

[IS-856]A duration of time specified by 1.66... ms.

Slot Cycle

[IS-95, IS-2000]A periodic interval at which a mobile station operating in the slotted mode monitors the Paging Channel.

Slotted Mode

[IS-95, IS-2000]An operation mode of the mobile station in which the mobile station monitors only selected slots on the Paging Channel. See also Slot Cycle.

SLP

[IS-856]Signaling Link Protocol (SLP) provides best-effort and reliable-delivery mechanisms for signaling messages. See also SNP.

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Smin

The minimum signal level required to meet some criteria of Eb/N0. Also referred to as receiver sensitivity.

SNP

[IS-856]Signaling Network Protocol (SNP) provides message transmission services for signaling messages. The protocols that control each layer use SNP to deliver their messages to their peer protocols. See also SLP.

Soft Handoff

A handoff occurring while the mobile station is on a Traffic Channel. This handoff is characterized by commencing communications with a new base station on the same CDMA frequency assignment before terminating communications with the old base station. See also Hard Handoff and Softer Handoff.

Softer Handoff

This refers to the handoff process that is handled by a channel element which supports multiple sectors. The user terminal, during the (inter-sector) soft handoff, will communicate through two sectors (radios) with only one channel element. Softer handoff is a subset of soft handoff.

SOM

Start-of-Message Bit.

Space Time Spreading

A forward link transmission method which transmits all forward link channel symbols on multiple antennas, and spreads the symbols with complementary Walsh or quasi-orthogonal functions.

Spreading

When two signals, b(t) and c(t), are multiplied together, the resulting signal, b(t)c(t), will have the same bit (or chip) period as the faster signal (wider bandwidth); e.g., c(t). See also Scrambling.

Spreading Gain

Spreading gain or processing gain is achieved when noise components, or noise-like components, remain spread when the original signal is de-spread. The original signal appears to have gained energy relative the noise. It can also be seen as if the noise has been suppressed.

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Spreading Rate (SR)

[IS-2000]The PN chip rate of the Forward CDMA Channel or the Reverse CDMA Channel, defined as a multiple of 1.2288 Mcps.Spreading Rate 1 (SR1) is often referred to as "1X." A SR1 Forward CDMA Channel uses a single direct-sequence spread carrier with a chip rate of 1.2288 Mcps. A SR1 Reverse CDMA Channel uses a single direct-sequence spread carrier with a chip rate of 1.2288 Mcps.Spreading Rate 3 (SR3) is often referred to as "3X." A SR3 Forward CDMA Channel uses three direct-sequence spread carriers (see multi-carrier) each with a chip rate of 1.2288 Mcps. A SR3 Reverse CDMA Channel uses a single direct-sequence spread carrier with a chip rate of 3.6864 Mcps.

sps

Symbols per second.

SR

See Spreading Rate.

Station Class Mark (SCM)

An identification of certain characteristics of a mobile station.

Stream Layer

[IS-856]The Stream Layer provides multiplexing of distinct streams. Stream 0 is dedicated to signaling and defaults to the default signaling stream (SNP / SLP), and Stream 1 defaults to the default packet service (RLP). Stream 2 and Stream 3 are not used by default. See also Layering.

STS

See Space Time Spreading.

Subnet Mask (of length n)

A 128-bit value whose binary representation consists of n consecutive '1's followed by 128-n consecutive '0's.

Suspended Mode

[IS-856]The suspended mode is similar to dormant mode, but a connection can be established without using the Access State. See also Dormant Mode.

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Sweden

A country of northern Europe on the eastern Scandinavian Peninsula. The region was settled by Germanic tribes probably in Neolithic times, and by the 10th century A.D. the Swedes had extended their influence as far as the Black Sea. During the 14th century Sweden and Norway, and for a while Denmark, formed a union, but in the 16th century the Swedes revolted and established a separate state. By the 17th century Sweden was a major European power, controlling most of the Baltic coast. It lost much of its territory in the Great Northern War (1700-1721) but acquired Norway (1814) in the Napoleonic Wars, ruling it until 1905. Stockholm is the capital and the largest city.Area: 173,620 sq. miles (449,674 sq. km)Population: 8,940,788 (year 2002).

Symbol

See Code Symbol and Modulation Symbol.

Symbol Puncturing

The process of deleting modulation symbols. See also Symbol Repetition.

Symbol Repetition

The process of repeating modulation symbols. See also Symbol Puncturing.

Sync Channel

[IS-95, IS-2000]A code channel in the Forward CDMA Channel which transports the synchronization message to the mobile station.

Sync Channel Superframe

[IS-95, IS-2000]An 80 ms interval consisting of three Sync Channel frames (each 26.66... ms in length). See also Sync Channel.

System

A system is a cellular telephone service that covers a geographic area such as a city, metropolitan region, county, or group of counties. See also Network.

System Identification (SID)

A number uniquely identifying a cellular system. See also System.

System Time

The time reference used by the system. System time is synchronous to UTC (Universal Coordinated Time) time (except for leap seconds) and uses the same time origin as GPS time. All base stations use the same system time (within a small error tolerance). Mobile stations use the same system time, offset by the propagation delay from the base station to the mobile station. See also Universal Coordinated Time.

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T TA

The specified time associated with waiting for an acknowledgement by the mobile station during the access procedure. See also Access Procedure.

Tb

The time period between bits, or bit interval.

Tc

The time period between chips, or chip interval.

TD

Transmit Diversity schemes, including OTD and STS.

Termination

See Mobile Station Terminated Call.

Timer-Based Registration

A registration method in which the mobile station registers whenever a counter reaches a predetermined value.

Time Reference

A reference, established by the mobile station, that is synchronous with the earliest arriving multipath component used for demodulation.

TMSI

Temporary Mobile Subscriber Identity. See also IMSI.

Traffic Channel

A communication path between a mobile station and a base station used for user and signaling traffic. The term Traffic Channel often implies a Forward Traffic Channel and Reverse Traffic Channel pair. See also Forward Traffic Channel and Reverse Traffic Channel.

Traffic Channel Preamble

A sequence of all-zero frames that is sent at the by the mobile station on the Reverse Traffic Channel. The Traffic Channel preamble is sent during initialization of the Traffic Channel.

Traffic Channel State

[IS-95, IS-2000]In the Traffic Channel State, the mobile station communicates with the base station using the Forward and Reverse Traffic Channels.

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Transmit Diversity Pilot Channel

[IS-2000]An unmodulated, direct-sequence spread spectrum signal transmitted continuously by a CDMA base station to support forward link transmit diversity. The Forward Pilot Channel and the Transmit Diversity Pilot Channel provide phase references for coherent demodulation of Forward CDMA Channels which employ transmit diversity.

Turbo Code

A type of error-correcting code. A code symbol is based on the outputs of the two recursive convolutional codes (constituent codes) of the turbo code. See also Forward Error Correction.

Tx

Transmit.

U Universal Coordinated Time (UTC)

An internationally agreed-upon time scale maintained by the Bureau International de l’Heure (BIH) used as the time reference by nearly all commonly available time and frequency distribution systems i.e., WWV, WWVH, LORAN-C, Transit, Omega and GPS.

UATI

[IS-856]Unicast Access Terminal Identifier. See also Access Terminal.

Uplink

See Reverse Link.

UTC

Universal Temps Coordine. See Universal Coordinated Time.

V Variable Data Rates

The operation of a Traffic Channel where the transmitter can change the data rate among a set of possible choices on a frame-by-frame basis.

Variable-rate Supplemental Channel

[IS-2000]The operation of the Forward Supplemental Channel and the Reverse Supplemental Channel where the transmitter can change the data rate among a set of possible choices on a frame-by-frame basis.

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Virtual Soft Handoff

[IS-856]When the access terminal is receiving the Forward Traffic Channel, virtual soft handoff is the process of transferring the Traffic Channel to another base station within the Active Set.

Vocoder

Abbreviation for voice-coder. A device that usually consists of a speech analyzer, which converts analog speech waveforms into narrowband digital signals, and a speech synthesizer, which converts the digital signals into artificial speech sounds.

Voice Privacy

The process by which user voice transmitted over a Traffic Channel is afforded a modest degree of protection against eavesdropping over the air.

W Walsh Chip

The shortest identifiable component of a Walsh or quasi-orthogonal function. There are 2N Walsh chips in one Walsh function where N is the order of the Walsh function.

Walsh Function

One of 2N time orthogonal binary functions (note that the functions are orthogonal after mapping '0' to +1 and '1' to -1). See also Walsh Chip.

Z Zone-Based Registration

An autonomous registration method in which the mobile station registers whenever it enters a zone that is not in the mobile station’s zone list. See also Registration Zone.

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