owa200002 wcdma ran basic principle.pdf

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OWA200002 WCDMA RAN Basic

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2HUAWEI TECHNOLOGIES CO., LTD. Page 2All rights reserved

Chapter 1 Radio Transmission Environment Chapter 1 Radio Transmission Environment

Chapter 2 CDMA FundamentalChapter 2 CDMA Fundamental

Chapter 3 Performance Enhancement MethodsChapter 3 Performance Enhancement Methods

Chapter 4 WCDMA FDD ModeChapter 4 WCDMA FDD Mode



Multi-path Environment

Time

Receivedsignal

Transmitted

signal

Radio environment is very complex. The transmission signal of BSreaches the UE through all kinds of paths including reflection,scattering and diffraction. The received signals is different in power and delay time. But the multi-path signal can be used by RAKE receiver through multi-path combination.



Fading

Distance(m)

Received Power(dBm)

10 20 30

-20

-40

-60

Slow fading

Fast fading



Frequency Selection of Fading

NarrowbandSystem

NarrowbandSystem

Fading

Transmit Signal Received Signalff

P(f) P(f)

Fading

Transmit Signal Received Signalff

P(f) P(f)

BroadbandSystem

BroadbandSystem



Chapter 1 Radio Transmission EnvironmentChapter 1 Radio Transmission Environment







2.1 Multiple Access Technology and Duplex Technology2.1 Multiple Access Technology and Duplex Technology

2.2 CDMA Principle and RAKE Technology2.2 CDMA Principle and RAKE Technology



Multiple Access Technology and Duplex Technology

l Multiple access technology

[Time division multiple access (TDMA)

[Frequency division multiple access (FDMA)

[Code division multiple access (CDMA)

l Duplex technology

[Time division duplex (TDD)

[ Frequency division duplex (FDD)

In third generation mobile communication systems, TD-SCDMA adopts

time division duplex (TDD); WCDMA and cdma2000 adopt frequency division duplex (FDD). WCDMA FDD mode has been consolidated with TD-SCDMA.



Traffic channels: differentusers are assigned unique code and transmitted over the same frequency band, for example, WCDMA and CDMA2000

Traffic channels: different frequency bands are allocated to different users,for example, AMPS and TACS

Traffic channels: different time slots are allocated to different users, for example, DAMPS and GSM

Freque

ncyTime

Power

Freque

ncyTime

Power

Freque

ncyTime

Power

FDMA

TDMA

CDMA

User

User

User User

User User

Multiple Access Technology

Frequency Division Multiple Access: frequency division, sometimes called channelization, means dividing the whole available spectrum into many single radio channels (transmit/receive carrier pair). Each channel can transmit one-way voice or control information. Under the control of the system, any user can be accessed to any of these channels. Analog cellular system is a typical example of FDMA structure. Similarly, FDMA can also be used in a digital cellular system,except that pure frequency division is not adopted. For example, FDMA is adopted in GSM and CDMA.

Time Division Multiple Access means that the wireless carrier of one bandwidth is divided into multiple time division channels in terms of time (or called timeslot). Each user occupies a timeslot and receives/transmits signals within this specified timeslot. Therefore, it is called time division multiple access. This multiple access mode is adopted in both a digital cellular system and a GSM. TDMA is a complex architecture and the simplest case is that a single channel carrier is divided into many different timeslots, each of which transmits one-way burst-oriented information. The key part in TDMA is the user part, in which each user is allocated with one timeslot (allocated when a call begins). The user communicates with a base station in a synchronous mode and counts the timeslot. When his own timeslot comes, the mobile station starts a receiving and demodulation circuit to decode the burst-oriented information sent from the base station. Likewise, when a user wants to send any information, he should first cache


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Characteristics of CDMA System

l High Spectral Efficiency

[ Frequency multiplex coefficient is 1.

l soft capacity

[Quality

[Coverage

[ Interference

l Self-interference system

[A UE transmission power is interference for another UE.

In CDMA, channel data rate is smaller than delay extension. So RAKE Rx technology can be used.


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2.1 Multiple Access Technology and Duplex Technology2.1 Multiple Access Technology and Duplex Technology

2.2 CDMA Principle and RAKE Technology2.2 CDMA Principle and RAKE Technology


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correlationl Correlation is a measure of similarity of between any two arbitrary signals.

l EXAMPLE:

-1 1 -1 1 1 1 1 1

-1 1 -1 1Zero correlation

Orthogonal signals

-1 1 -1 1-1 1 -1 1 1 1 1 1

1 correlationIdentical signals

+10-1+10-1

+10-1

+10-1


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OVSF&WalshCreating the orthogonal code sequencesCreating the orthogonal code sequences

SF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

Channelisation code uses OVSF code, for keeping the orthogonality of different subscriber physical channels. OVSF can be defined as the code tree illustrated in the following diagram.

Channelisation code is defined as Cch,SF, k,, where, SF is the spreading factor of the code, and k is the sequence of code, 0kSF-1.Each level definition length of code tree is SF channelisation code, and the left most value of each channelisation code character is corresponding to the chip which is transmitted earliest.


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Autocorrelation

l Autocorrelation is related to the muti-path interference characteristic.

Delay time sequence correlation0 -1 -1 -1 1 1 -1 1 11 -1 -1 1 1 -1 1 -1 -1/72 -1 1 1 -1 1 -1 -1 -1/7 3 1 1 -1 1 -1 -1 -1 -1/7 4 1 -1 1 -1 -1 -1 1 -1/7 5 -1 1 -1 -1 -1 1 1 -1/76 1 -1 -1 -1 1 1 -1 -1/7

Delay time (chip)

Correlation

1

Example: Example: --1 1 --1 1 --11 1 1 1 1 --1 11 1


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Configuration of Gold Sequence Generator

Gold sequence is used as scrambling code in WCDMAGold sequence is used as scrambling code in WCDMA

clong,1,n

clong,2,n

MSB LSB


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Spreading

Despreading

Chip

Symbol

Data

Spreading code

Spreading signal=Datacode

Data=Spreadingcode

1

-1

1-1

1-1

1-1

1-1

Spreading code

Spreading and Despreading (DS-CDMA)

Suppose bit sequence modulated with BPSK is adopted for the subscriber data, with a rate of R, then 1 value is adopted for the bit of subscriber data.

The spreading here means to multiply each subscriber data bit with the spreading code chip including N bits..Assume N=8,then data rate after spreading will be 8R, with same random attribute as the spreading code.Wename its spreading factor as 8. And the broad band signal obtained after spreading will be sent to the receiving end via the radio channel.

As the product of signal rate and factor 8 equals to the bandwidth spreading of subscriber data signal,CDMA system is also called the spreading system.

During dispreading, the spread subscriber data will be multiplied, bit duration by bit duration, with the same 8 code chips that are used during the spreading of these bits.If only excellent synchronization can be realized between the spread subscriber signal and the despreading code, can the subscriber bit sequence be retrieved.The despreading operation restores the signal bandwidth to the original value R.


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Desired signal

Other users signal

Desired spreadingsignal

Spreading code

Data afterdespreading

Other spreadingsignal

Other signal afterintegration

1

-1

1

-1

1

-18

-8

1-18-8

Data afterintegration

Other signal after despreading

Spreading and Despreading (DS-CDMA)

During the process of receiving the expected correct signal that belongs to the subscriber, complete synchronous despreading codes are adopted for the despreading operation. After obtaining the despreading data, the correlation receiver integrates the resulting products, then get the integration data.

Signals of other subscribers using different spreading codes are actually the interference signals to the first subscriber. In this case, multiply the signals and the despreading code of the first subscriber to get the despreading signal, and then perform integration. Finally, an interference signal with a signal value fluctuating along with 0 will be got.It can be viewed that the signal amplitude of the subscriber increases by 8 times than that of the other interference systems in average. That is to say, the correlation detection increases the expected subscriber signal by the multiple of spreading factor value within the interference of CDMA system.This effect is called processing gain, and it is the basic characteristic of the spreading system.Elementarily, this kind of correlation receivers are adopted for the BTS and UE in the WCDMA system.Because the existence of multipath propagation and multi receiving antennas, multiple correlation receivers are necessary for retrieving the signal energy from all the paths or antennas.And the collection of these correlation receivers forms the CDMA RAKE receiver.


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Sourcecoding

Channel coding Spreading Modulation

Sourcedecoding

Channel decoding Despreading Demodulation

Radio channelRadio channelRadio channel

Processing Procedure of CDMA System


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Spectrum Analysis of Spreading & Despreading

Spreading code

Spreading code

Signal Combination

Narrowband signalf

P(f)

Broadband signal

P(f)

f

Noise

P(f)

f

Noise+Broadband signal

P(f)

f

Recovered signal P(f)

f


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Principle of RAKE Receiver

Receive set

Correlator 1

Correlator 2

Correlator 3

Searcher correlator Calculate the time delay and signal strength

CombinerThe

combined signal

tt

s(t) s(t)

RAKE receiver help to overcome on the multi-path fading and enhance the receive performance of the system


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Structure of RAKE Receiver

Q

I

Combiner

I

MatchedFilter

PhaseRotator

Channelestimator

DelayEqualizer

I

Q

Path 1

Path 2

Path 3

Input signal

Correlator

Codegenerators Q

For the digitized signals input to the baseband, despreading and integration of subscriber data symbols is completed via the correlator and local code generator, specifics are as follows:Channel estimator uses the pilot signal to estimate the channel status; Phase spinner deletes the phase affection caused by the channel from the received signal according to the estimated channel status. The function of delay estimation is to obtain the signal energy distribution at different delay positions via the matching filter, and identify the multipathswith large energy, and allocate their time values to different receive paths of the RAKE receiver.The delay equalizer is to compensate the difference of symbol arriving time for each path.At last, the RAKE combiner adds the symbols after channel compensation to provide multipath diversity to withstand fading.From the aspect of realization, the processing of RAKE receiver can be based on either chip level or symbol level.The correlator, local code generator and matching filter belong to the chip level processing, and this is generally realized via ASIC device; Channel estimation, phase spinning and combination belong to symbol level processing, and this is realized via DSP.Though the realization methods and functions of the RAKE receiver between UE and BTS are different, the principles are complete the same.


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Advantages of CDMA

l RAKE receiver is adopted[The time diversity effect generated by channel

coherence time is efficiently used.l frequency diversity [Wideband frequency spectrum

l Higher interference tolerance and security performance[Low signal transmission power

l Great flexibility in carrying multiple services with largely different bit rate and QoS requirement.[Different spreading factors for different services with

different data ratesl High spectral efficiency[All users can share the same frequency spectrum

simultaneously.l Supporting soft handover and softer handover.


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24


HSDPA Key Techniques - OverviewHSDPA Key Techniques - Overview

AMC Fast SchedulingHARQHybrid ARQ

16QAMSF16, 2ms and CDM/TDM 3 New Physical Channels


25


l AMC (Adaptive Modulation & Coding) based on Channel Quality Feedback

[ Adjust data rate to compensate channel conditions

Good channel condition Higher rate

Bad channel condition Lower rate

[ Adjust the coding rate to compensate channel conditions

Good channel condition 3/4

Bad channel condition 1/3

[ Adjust the modulation scheme to compensate channel conditions

Good channel condition 16QAM

Bad channel condition QPSK

l Channel Quality Feedback (CQI)

[ UE measures the channel quality (SNR) reports (every 2ms or more cycle) to Node-B

[ Node-B choose modulation and block size, data rate primarily based on CQI

HSDPA Key Techniques - AMCHSDPA Key Techniques - AMCHigh data rate

Low data rate


26


HSDPA Key Techniques - HARQHSDPA Key Techniques - HARQConventional ARQReceived Transmitted blocks are decodedChecked for CRC errors on decoded blocksIf errors

discard the error bolcksRequest the trasmitter for retransmission

Hybrid ARQReceived Transmitted blocks are decodedChecked for CRC errors on decoded blocksIf errors

Store the erroneous block without discardingRequest the trasmitter for retransmissionCombine the received re-trasmission with previously received trasnmisison

HARQ with Soft Combining

NodeB

UE Packet1? N

Packet 1 Packet 1

Packet 1

Packet1?+

A

Packet2

Transmitter

Receiver


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HSDPA Key Techniques - Fast scheduling

l Scheduler may be based on

[ CDM, TDM

[ Channel condition

[ Amount of data waiting in the queue (delay)

[ Fairness (satisfied users)

[ Cell throughput, etc

Scheduling determines which user

shall be transmitted.


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HSDPA Key Techniques CDM and TDM

Channelization codes allocatedfor HS-DSCH transmission

8 codes (example)SF=16

SF=8

SF=4

SF=2

SF=1

User #1 User #2 User #3 User #4

TTI

Shared channelization

codes

10 ms20 ms40 ms80 ms

Earlier releases

2 msRel 5 (HS-DSCH)

sub-frames (2560 chips)


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HSDPA Key Techniques 16QAM

l HSDPA Modulation

[QPKS

[16QAM


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Introduction to Diversity Technique

l Diversity technique is used to obtain uncorrelated signals for combining

l Reduce the effects of fading

[ fast fading caused by multi-path

[ Slow fading caused by shadowing

l Improve the reliability of communication

l Increase the coverage and capacity

l Macroscopic diversity

[ Soft handover and softer handover

[ Reduce large-scale fading

l Microscopic diversity

Diversity technology means that after receiving two or more input signals with mutually uncorrelated fading at the same time, the system demodulates these signals and adds them up. Thus, the system can receive more useful signals and overcome fading.

A mobile communication channel is a multi-path fading channel and any transmitted signal reaches a receive end by means of multiple transmission paths, such as direct transmission, reflection, scatter, etc. Furthermore, with the moving of a mobile station, the signal amplitude, delay and phase on various transmission paths vary with time and place. Therefore, the levels of received signals are fluctuating and unstable and these multi-path signals, if overlaid, will lead to fading. The mid-value field strength of Rayleigh fading has relatively gentle change and is called Slow fading. And it conforms to lognormal distribution.

Diversity technology is an effective way to overcome overlaid fading. Because it can be selected in terms of frequency, time and space, diversity technology includes frequency diversity, time diversity and space diversity.


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Microscopic Diversity

l Time diversity

[Channel coding, Block interleaving, error-correction

l Frequency diversity

[The user signal is distributed on the whole bandwidth frequency spectrum

l Space diversity

[Receive diversity

[Transmit diversity

l Polarization diversity

[Vertical polarization

[Horizontal polarization





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Basic Combining Methods

l Maximal-Ratio Combiner

[The multi-path signals are weighted proportional to their signal SNR and then summed.

l Equal-Gain Combiner

[Equal-gain combining is similar to maximal-ratio combining, but there is no attempt to weight the signal before addition.

l Selection Combiner

[Choose the signal with the highest instantaneous quality, so the output quality is equal to that of the best incoming signal.





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Smart Antennal Reduce interference

l Increase coverage and capacity

Wanted signal

interference





34


Smart Antenna

Omni antenna Directional antenna Smart antenna





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Characteristics of WCDMA FDD

l Channel bandwidth: 5MHz

l Chip rate: 3.84Mcps

l Frame length: 10ms

l Voice coding: AMR (Adaptive Multi-Rate)

l Uplink and downlink modulation: QPSK/QPSK

l Coherence demodulation aided with pilot

l Fast closed loop power control: 1500Hz

l Handover: soft/hard handover

l Support synchronous and asynchronous NodeBoperation

1,The DS-CDMA system with a bandwidth of approximately 1MHz, i.e. IS-95, is generally named as narrowband CDMA system.But WCDMA owns a chip rate of 3.84Mcps, bringing approximately 5MHz carrier bandwidth.This feature enables the system to support higher bit rate, and at the same time brings other benefits, for example, increasing of multi-path diversity.

2,In IS-95, only coherence detection is used in the downlink, but in WCDMA, coherence detection based on pilot symbol or common pilotis adopted for both the uplink and the downlink, increasing the coverage scope and the capacity of the uplink.

3,IS-95 only uses closed loop power control in the uplink, while WCDMA uses this in both of the uplink and the downlink.With the closed loop power control used in the downlink, link performance and downlink capacity is improved.

4,IS-95 system mainly aims at macro cell. Because BTS synchronizationis necessary, BTS is generally placed on the roof, etc. for the sake of receiving GPS signal.In this case, a global time reference can be used. But this application is difficult to carry out in the places where it is hard to receive the GPS signals. WCDMA system supports asynchronous BTS operation, and it may not use the global reference, thus it is different with the IS-95 system requiring BTS synchronization operating


37


Characteristics of WCDMA FDD

l Satisfy the minimum performance requirement of IMT2000

l Compatible with GSM-MAP core network

l Comparatively steady version R99 has been released

l Support open loop and closed loop transmit diversity mode

l Support Common Packet Channel(CPCH) and Downlink Share Channel, adapt to Internet data access mode

l Support macro diversity, selection diversity of NodeBlocation

l Support different fast power control algorithms and open loop, out loop power control

l Fully support UE locating services


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WCDMA Voice Evolution

l Adopt AMR voice coding, and support voice quality of 4.75Kbps ~ 12.2Kbps

l Adopt soft handover and transmit diversity to improve system capacity

l Provide high fidelity voice mode

l Fast power control


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Data Service Evolution of WCDMA

l Support maximum 2Mbps data servicel Support packet switchl Adopt ATM platform currentlyl Provide QoSl Common Packet Channel(CPCH) and Downlink

Share Channel(DSCH) can support Internet packet services better

l Provide mobile IP service(dynamic allocation of IP addresses)

l TFCI domain provides dynamic data ratel Provide high-quality support for uplink-downlink

symmetric data service, such as voice, video phone, conference TV


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