an introduction to cdma air interface

An Introduction to CDMA Air Interface:

TIA/EIA/IS-95A

Advanced Technology Center

Computer & Communications Research Laboratories

Industrial Technology Research Institute

Ray-Guang Cheng

[email protected]

Contents

• Introduction

• Forward CDMA Channel

• Reverse CDMA Channel

Chung-Wei Ku

ATC/CCL/ITRI

Advanced Technology CenterAdvanced Technology CenterAdvanced Technology CenterAdvanced Technology CenterComputer & Communications Research LaboratoriesIndustrial Technology Research Institute

CDMA Around the World

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ATC/CCL/ITRI


Multiple Access

• FDMA

– Advanced Mobile Phone Service (AMPS) and Total Access

Communications System (TACS)

– AMPS systems use 30 kHz "slices" of spectrum for each channel

– Narrowband AMPS (NAMPS) requires only 10 kHz per channel

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ATC/CCL/ITRI


– Narrowband AMPS (NAMPS) requires only 10 kHz per channel

– TACS channels are 25 kHz wide

• TDMA

– IS-54 systems, designed to coexist with AMPS systems, divide 30 kHz of

spectrum into three channels

– PDC divides 25 kHz slices of spectrum into three channels

– GSM systems create 8 time-division channels in 200 kHz wide carriers

Multiple Access

• CDMA

– unique digital codes are used to differentiate subscribers

– codes are shared by both MS and BS

– all users share the same range of radio spectrum

• Benefits of CDMA:

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ATC/CCL/ITRI


• Benefits of CDMA:

– Capacity increases: 8 to 10 times (AMPS); 4 to 5 times (GSM)

– Improved call quality

– Simplified system planning

– Enhanced privacy

– Improved coverage characteristics

– Increased talk time for portables

– Bandwidth on demand

CDMA

• There are two CDMA common air interface standards:

– Cellular (824-894 MHz) - TIA/EIA/IS-95A

– PCS (1850-1990 MHz) - ANSI J-STD-008

They are very similar in their features, with exceptions of the frequency plan, mobile identities, and related message fields.

Chung-Wei Ku

ATC/CCL/ITRI


frequency plan, mobile identities, and related message fields.

• IS-95A

– 45 MHz spacing for forward & reverse channel

– Permissible frequency assignments are on 30 kHz increments

– W/R = 10 log (1.2288 MHz/9600Hz) = 21 dB for the 9600 bps rate set

• ANSI J-STD-008

– 80 MHz spacing for forward & reverse channel

– Permissible frequency assignments are on 50 kHz increments

Frequency Plan of IS-95A

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ATC/CCL/ITRI


Frequency Plan of ANSI J-STD-008

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ATC/CCL/ITRI


Forward CDMA Channel of IS-95A

• From BSS to MS

• It carries traffic, a pilot signal, and overhead information.

• Pilot is a spread but unmodulated DSSS signal.

• Pilot and overhead channels establish the system timing and

station identity.

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station identity.

• Pilot channel is also used in the mobile-assisted handoff

(MAHO) process as a signal strength reference.

• FEC code rate is 1/2 and the PN rate is 1.2288 MHz (1.2288

MHz = 128*9600 bps).

Forward Link Channel Parameters

Channel Sync Paging Traffic

Data rate 1200 4800 9600 1200 2400 4800 9600 bps

Code repetition 2 2 1 8 4 2 1

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Code repetition 2 2 1 8 4 2 1

Modulation symbol rate 4800 19,200 19,200 19,200 19,200 19,200 19,200 sps

PN chips/modulation symbol 256 64 64 64 64 64 64

PN chips/bit 1024 256 128 1024 512 256 128

Signal Structure

• The forward link consists of up to 64 logical channels (code

channels).

• Code channels is one of a set of 64 so-called Walsh functions.

• Only whole periods of the Walsh functions occur in each code

symbol, the Walsh makes the channels completely separable in

Chung-Wei Ku

ATC/CCL/ITRI


symbol, the Walsh makes the channels completely separable in

the receiver.

• Each forward code channel is spread by the Short Code, which

has I- and Q-components.

• The two coded, covered, and spread streams are vector-

modulated on the RF carrier. The spreading modulation is thus

QPSK, superimposed on a BPSK code symbol stream.

Overhead Channels

• There are three types of overhead channel in the forward link:

– pilot, is required in every station

– sync

– paging

• Pilot channel

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ATC/CCL/ITRI


• Pilot channel

– pure short code with no additional cover or information content

– always code channel zero

– a demodulation reference for the mobile receivers and for handoff level

measurements

– carries no information

– all stations use the same short code, distinguished by the phase

– period of the short code, 215= 26.667 ms at the 1.2288 MHz chip rate

Overhead Channels

• Pilot channel (Conti.)

– pilot phases always be assigned to stations in multiples of 64 chips,

giving a total of 215-6 = 512 possible assignments

– 9-bit number that identifies the pilot phase assignment is called the Pilot

Offset

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ATC/CCL/ITRI


• Sync Channel

– sync channel carries timing and system configuration information

– data rate is always 1200 bps

– interleaver period is also 80/3 = 26.667 ms, simplifies finding frame

boundaries, once the mobile has located the pilot

– code period ambiguity is then resolved by the long code state and system

time fields

Overhead Channels

• Paging channel

– used to communicate with MSs when they are not assigned to a traffic

channel

– successful accesses are normally followed by an assignment to a

dedicated traffic channel

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ATC/CCL/ITRI


– paging channel may run at either 4800 or 9600 bps

– each BS must have at least one paging channel per sector, on at least one

of the frequencies in use

Traffic Channel

• Traffic channels

– assigned dynamically, in response to MS accesses, to specific MS

– always carries data in 20 ms frames

– carry variable rate traffic frames, either 1, 1/2, 1/4, or 1/8 of 9600 bps

– rate variation is accomplished by 1, 2, 4, or 8-way repetition of code

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ATC/CCL/ITRI


– rate variation is accomplished by 1, 2, 4, or 8-way repetition of code

symbols, but the energy per bit approximately constant

– rate is independently variable in each 20 ms frame

– the 800 bps reverse link power control subchannel is carried on the traffic

channel by puncturing 2 from every 24 symbols transmitted.

• Timing

– all base stations must be synchronized within a few microseconds

Reverse CDMA Channel of IS-95

• From MS to BSS

• It carries traffic and signaling information.

• FEC code rate is 1/3, the code symbol rate = 28,800 symbols/sec,

6 code symbols/modulation symbol, and the PN rate is 1.2288

MHz

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ATC/CCL/ITRI


MHz

• modulation is 64-ary orthogonal Walsh functions, each period of

the Walsh function is repeated for four chips of the PN code

• Walsh symbol rate is 1.2288 MHz/(4 chips per Walsh chip)/(64

Walsh chips per Walsh symbol) = 4,800 modulation symbols/

second

Reverse CDMA Channel Parameters, Rate Set 1

Channel Access Traffic

Data rate 4,800 1,200 2,400 4,800 9,600 bps

Code Rate 1/3 1/3 1/3 1/3 1/3

Symbol Rate before Repetition 14,400 3,600 7,200 14,400 28,800 sps

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ATC/CCL/ITRI


Symbol Rate before Repetition 14,400 3,600 7,200 14,400 28,800 sps

Symbol Repetition 2 8 4 2 1

Symbol Rate after Repetition 28,800 28,800 28,800 28,800 28,800 sps

Transmit Duty Cycle 1 1/8 1/4 1/2 1

Code Symbols/Modulation Symbol 6 6 6 6 6

PN Chips/Modulation Symbol 256 256 256 256 256

PN chips transmitted/bit 256 128 128 128 128

Signal Structure

• Reverse CDMA Channel consists of 2 42-1 logical channels

• One of the logical channel is permanently and uniquely associated

with each MS. The channel does not change upon handoff.

• Reverse link addressing is accomplished through manipulation of

period 2 42-1 Long Code, which is part of the spreading process.

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ATC/CCL/ITRI


period 2 42-1 Long Code, which is part of the spreading process.

• The reverse CDMA Channel does not use strict orthogonality in

any sense to separate logical channels. Rather, it uses a very long

period spreading code, in distinct phases. The correlations

between stations are not zero, but they are acceptably small.

Handoff

• CDMA is specifically designed not only to reduce handoff

failures but also to provide seamless service.

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Handoff

• Steps in a handoff

– Starting in a state where only one cell is supporting the call in question.

– Informing the candidate cell of the imminent handoff

– Signaling the mobile to begin executing the handoff.

– New cell beginning to service the mobile

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– New cell beginning to service the mobile

– Mobile beginning to use the new cell

– Entering the mid-handoff state (prolonged only in CDMA)

– Mobile discontinuing use of the old cell

– Old cell stopping service to the mobile

– Ending in a state where the new cell is supporting the call in question

AMPS v.s. CDMA

• Difference between AMPS & CDMA

– CDMA handoffs do not normally require frequency tuning.

– CDMA requires change of the code channel in the forward CDMA channel.

– No tuning, either frequency or code channel is required in the reverse

CDMA channel at any time.

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CDMA channel at any time.

• AMPS

– Hard handoff (communication is interrupted briefly)

– not simultaneous communication with more than one BS

– BS do the signal quality measurement

CDMA Protocol

Upper Layers

(Primary Traffic)

Upper Layers

(Secondary Traffic)Layer 3 (Mobile Station Control Processes)

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Layer 2

(Primary Traffic)

Layer 2

(Secondary Traffic)

Layer 2

(Signaling)

Multiplex Sublayer (Traffic Channel)

Layer 2

(Link Layer)

Paging & Access

Channels

Layer 2

Sync

Channels

Layer 1 (Physical Layer)

Multiplex Option Information

Format Bits Primary

Traffic

Signaling

Traffic

Secondary

Traffic

Transmit

Rate

(bps)

Mixed

Mode (

MM )

Traffic

Type (

TT )

Traffic

Mode

( TM )

Bits/frame Bits/frame Bits/frame

0 - - 171 0 0

1 0 00 80 88 0

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ATC/CCL/ITRI


1 0 01 40 128 0

1 0 10 16 152 0

1 0 11 0 168 0

1 1 00 80 0 88

1 1 01 40 0 128

1 1 10 16 0 152

9600

1 1 11 0 0 168

4800 - - - 80 0 0

2400 - - - 40 0 0

1200 - - - 6 0 0

Primary and Signaling Traffic

MM

=0

MM

=1

MM

=1

MM

TT

=0

TT

=0

TT

TM

=00

TM

=01

TM

Primary Traffic = 171 bits

Primary Traffic

= 80 bits

Signaling Traffic

= 88 bits

Primary Traffic

= 40 bits

Signaling Traffic

= 128 bits

Primary Traffic Signaling Traffic

9600 bps Primary

Traffic only

Dim & Burst with rate 1/2

primary & signaling traffic




172 bits

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ATC/CCL/ITRI


MM

=1

MM

=1

TT

=0

TT

=0

TM

=10

TM

=11

Primary Traffic

= 16 bits

Signaling Traffic

= 152 bits

Signaling Traffic = 168 bits






Blank & Burst with

signaling traffic only

4800 bps primary

traffic only

2400 bps primary

traffic only

1200 bps Primary

traffic only

80 bits

40 bits

16 bits

Secondary Traffic

MM

=1TT

=1

TM

=00

Primary Traffic

= 80 bits

Signaling Traffic

= 88 bits

MM

=1TT

=1

TM

=01

Primary Traffic

= 40 bits

Signaling Traffic

= 128 bits

Dim & Burst with rate

1/2 primary &

Secondary traffic


1/4 primary &

172 bits

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ATC/CCL/ITRI


=1 =1 =01 = 40 bits = 128 bits

MM

=1TT

=1

TM

=10

Primary Traffic

= 16 bits

Signaling Traffic

= 152 bits

MM

=1TT

=1

TM

=11Signaling Traffic = 168 bits

1/4 primary &

Secondary traffic


1/8 primary &

Secondary traffic

Blank & Burst with

Secondary traffic only

Sync Channel

• Signaling on all channels use a synchronized bit-oriented

protocol.

• Sync channel is used during the system acquisition stage.

• Sync channel frame length is the length of pilot PN sequence.

• Only the Sync Channel Message is sent on the sync channel.

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ATC/CCL/ITRI


• Only the Sync Channel Message is sent on the sync channel.

• MS

– obtains information from Sync Channel Message

– adjusts its timing to normal system timing

– begins monitoring its Paging Channel

Paging Channel

• Data rate: 2400, 4800, 9600 bps

• One 9600 bps Paging Channel can support 180 pages/sec.

• Paging Channel conveys four major types of messages:

– overhead

– paging

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– paging

– order

– channel assignment

• Configuration of the system is conveyed in four overhead messages:

– System Parameter Message

– Access Parameter Message

– Neighbor List Message

– CDMA Channel List Message

Overhead Messages

• System Parameter Message:

– configuration of the Paging Channel

– registration parameters

– parameters to aid pilot acquisition

• Access Parameter Message

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ATC/CCL/ITRI


• Access Parameter Message

– configuration of the Access Channel

– control parameters used to stabilize the Access Channel

• Neighbor List Message

– time offset of the pilot

– basic neighbor configuration

• CDMA Channel List Message

– CDMA frequency assignment that contain Paging Channels

Paging Channel Messages

• Page Message:

– contains pages to one or more mobile stations.

• Order Message:

– a broad class of messages used to control a particular MS.

• Channel Assignment Message:

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• Channel Assignment Message:

– let BS to assign a MS to the traffic channel

– change Paging Channel Assignment

– direct the MS to use the analog FM system

Access Channel

• Access Channel provides communications from MS to BS when

MS is not using a Traffic Channel.

• All Access Channel use 4800 bps mode

• Access Channel Message:

– call origination

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– call origination

– response to pages

– orders

– registrations

• One or more Access Channel are paired with every Paging Channel

• Control of Access Channel transmission is accomplished through

the Access Parameter Message sent on the Paging Channel

Framing and Signaling on the Traffic Channel

• Both forward & reverse Traffic Channels use 20 ms frames.

• Frames can be sent at 9600, 4800, 2400, or 1200 bps

• Signaling

– blank-and-burst signaling:

• sent at 9600 bps

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• replace one or more frames of primary traffic data

– dim-and-burst signaling:


• sends both signaling and primary traffic data in a frame

• degradation in voice quality is essentially undetectable

Traffic Channel Messages & Service Option

• Four types of control messages on the Traffic Channel

– messages controlling the call itself

– messages controlling handoff

– messages controlling forward link power

– messages for security and authentication

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– messages for security and authentication

• IS-95 supports different user applications, called service options

• Two different service options can be simultaneous supported:

– primary traffic

– secondary traffic

• MS can specify the desired service option at call origination.

IS-95 Standard

• Forward Link

– Pilot Channel

– Sync Channel

– Paging Channels (max. 7)

– Traffic Channels

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• Power Control Sub-Channel

• Reverse Link

– Access Channels


Forward CDMA Channel

• Forward link consists of up to 64 logical channels (code

channels)

• The code channels are distinguished by a set of 64 Walsh

functions

• Walsh function code number zero is always reserved as the pilot

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• Walsh function code number zero is always reserved as the pilot

• Short Code (with period 215, 27.667 ms at 1.2288 MHz)

– spreading the CDMA Forward Channel

– used in conjunction with the Long Code for spreading the CDMA

Reverse Channel

• Long Code (with period 242 - 1)

– spreading the CDMA Reverse Channel

– Long Code Mask serves as a reverse link address

Generation of Forward Code Channel

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Forward Channel Modulator (Spreading)

• Identical I, Q signals; but different I, Q PN sequences (short code)

• Transmitted power is reduced by 3, 6, or 9 dB for variable data

rates at 9.6 k, 4.8 k, 2.4 k, and 1.2 kbps

• QPSK modulation

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Forward Link Modulation Parameters

• 64 othoronal Walsh codes per sector to identify channels

– (S/N is not infinite due to AWGN, multipath, and the neighboring cell)

• Long code (period 2 42 -1) to scramble data

• DS at 1.2288 Mcps

• Every cell uses the same PN sequence (period 2 15 or 26.67ms)

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• Every cell uses the same PN sequence (period 2 15 or 26.67ms)

and is identified by a pre-defined offset (64 x n chips)

• Coherent QPSK demodulation

• Diversity

– time diversity: coding + interleaving

– path diversity: soft handoff and RAKE receiver

Logical Forward CDMA Channel

Forward CDMA Channel

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Pilot

Chan

Sync

Chan

W0 W32

Paging

Ch 1

W1

...Up

to W7

Paging

Ch 7

W8

...Up

to

Traffic

Ch N

Traffic

Ch 1

Traffic DataMobile Power

Control Sub-Channel

...

W31

Traffic

Ch 24Up

to

...

W63

Traffic

Ch 55

W33

Traffic

Ch 25

Pilot Channel

• Unmodulated signal

• Unique per sector/cell

• Signal level is 4~6 dB higher than traffic channel

• Perfect phase/time/signal strength reference for MS

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• Used in initial system acquisition and handoff for MS

Pilot

Channel

(All 0’s)

Walsh

Function

W0

PN Chips

1.2288 Mcps

Sync Channel

• 1200 bps

• To convey pilot PN sequence offset, time of day, and long code

state to allow immediate sync of MS to the network

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ATC/CCL/ITRI


Sync

Channel

Bits 1.2 kbps

Convolutional

Encoder

R=1/2, K=9

Code

Symbol

2.4 ksps

Symbol

Repetition

Block

Interleaver

Modulation

Symbol

4.8 ksps

Modulation

Symbol

4.8 ksps

Walsh

Function

W32

PN Chips

1.2288 Mcps

Sync Channel Frame Structure

• Sync channel message has length of 93 x N bits

• Sent in N superframes:

Message

Length

(in bytes)

8 bits

Data

N MSG = 2 ~ 1146 bits

CRC

30 bits

Padding

= …000...

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– 1 superframe (96 bits, 80 ms) = 3 sync channel frames

– 1 frame (32 bits, 26.67 ms) = 1-bit SOM + 31-bit data

– SOM = 1 : start of message

• Message contains:

– system identification (SID) and network identification (NID)

– PN sequence offset and long code state

– system time, leap seconds, offset from UTC, etc.

– paging channel data rate

Paging Channels

• 4.8 k or 9.6 k bps

• Same time alignment as the traffic channels

• To page MS and to process other ordersWalsh

Function

W p

1 ≤ p ≤ 7

Chung-Wei Ku

ATC/CCL/ITRI


Paging

Channel

Bits 4.8 kbps

or

9.6 kbps

Convolutional

Encoder

R=1/2, K=9

Code

Symbol

9.6 ksps

or

19.2 ksps

Symbol

Repetition

Block

Interleaver

Modulation

Symbol

19.2 ksps

Modulation

Symbol

19.2 ksps

PN Chips

1.2288 Mcps

Long Code

Mask for

Paging

Channel p

Long Code

Generator1.2288 Mcps

Decimator

19.2 ksps

19.2 ksps

Paging Channel Frame Structure

• Synchronized paging channel message has length of 47 x N or 95 x N bits

• Sent in N paging channel slots:

Message

Length

(in bytes)

8 bits

Data

N MSG = 2 ~ 1146 bits

CRC

30 bits

Padding

= …000...

Chung-Wei Ku

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• Sent in N paging channel slots:

– 1 slot (80 ms) = 8 paging channel half-frames

– 1 half-frame (10 ms, 48 or 96 bits) = 1-bit SCI + 47 (or 95)-bit data

– SCI = 1 : start of a paging channel message

• Message contains:

– system parameters

– access parameter (for access channel)

– channel assignment

– TMSI (temporary MS identification) assignment

Forward Traffic Channels

• 9.6, 4.8, 2.4, or 1.2 k bps; 20 ms frames

• Rate can be changed every frame

Forward Traffic

Channel

Information

Bits for User m8.6 kbps

Convolutional

Encoder

R=1/2, K=9

Symbol

Repetition

Add Frame

Quality Indicator

for 9600 &

4800 bps Rates

Add 8-bit

Encoder

Tail9.2 kbps 9.6 kbps 19.2 kbps

Chung-Wei Ku

ATC/CCL/ITRI


Bits for User m

(172, 80, 40 or

16 bits/frame)

4.0 kbps

2.0 kbps

0.8 kbps

R=1/2, K=9

Block

Interleaver

Modulation

Symbol

19.2 ksps

Modulation

Symbol

19.2 ksps

4800 bps RatesTail

4.4 kbps

2.0 kbps

0.8 kbps

4.8 kbps

2.4 kbps

1.2 kbps

9.6 kbps

4.8 kbps

2.4 kbps

Long Code

Mask for

Paging

Channel p

Long Code

Generator

1.2288 Mcps

Decimator

19.2 ksps Walsh

Function

W m

PN Chips

1.2288 Mcps

Decimator

MUX

Power

Control

Bits800 bps

800 Hz

Forward Traffic Channel Frame Structure

8

T

12

F

172

information bits

192 bits (20 ms)9600 bps

Frame

8880

96 bits (20 ms)4800 bps

Frame

Chung-Wei Ku

ATC/CCL/ITRI


8

T

8

F

80

information bits

Frame

8

T

8

F

40

information bits

48 bits (20 ms)2400 bps

Frame

8

T

8

F

16

information bits

24 bits (20 ms)1200 bps

Frame

F: Frame Quality Indicator (CRC)

T: Encoder Tail Bits

Forward Traffic Channel Frame Structure

• For signaling

Message

Length

(in bytes)

8 bits

Data

N MSG = 16 ~ 1160 bits

CRC

16 bits

Padding

= …000...

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ATC/CCL/ITRI


Logical Reverse CDMA Channel

Reverse CDMA Channel

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ATC/CCL/ITRI


Access

Ch 1

Access

Ch n... Traffic

Ch 1

Traffic

Ch m

Address by Long Code PNs

n ≤ 32 m ≤ 62

…

Access Channels

• To access the system, respond the page, make call origination

and process other messages between the MS and the BS

• 4.8 kbps slotted random access channel

• MS is identified by orthogonal of long codeAccess

Chung-Wei Ku

ATC/CCL/ITRI


Access

Channel

Information

Bits

(88 bits/frame)4.4

kbps

Convolutional

Encoder

R=1/3, K=9

Code

Symbol

14.4

ksps

Symbol

Repetition

Block

Interleaver

Modulator

Symbol

(Walsh chip)

PN Chips 1.2288 Mcps

Add 8-bit

Encoder

Tail 4.8

kbps

Code

Symbol

28.8

ksps

Code

Symbol

28.8

ksps

64-ary

Orthogonal

Modulator Long Code

Generator

Long Code Mask

4.8 ksps

Long code mask contents

110001111Access Channel

Number

Paging Channel

Number

Base Station

Identification

Pilot Offset for the

Forward Channel

Access Channel Long Code Mask

41 33 32 28 27 25 24 9 8 0

41 32 31 0

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ATC/CCL/ITRI


1100011000 Permuted ESN

Reverse Traffic Channel Public Long Code Mask

41 32 31 0

ESN=(E31, E30, E29, E28, E27, E26, E25, … , E2, E1, E0)

Permuted ESN=(E0, E31, E22, E13, E4, E26, E17, E8, E30, E21, E12, E3, E25, E16,

E7, E29, E20, E11, E2, E24, E15, E6, E28, E19, E10, E1, E23, E14,

E5, E27, E18, E9)

Access Channel

• Is used by the MS to initiate communication with the BS & to respond to

Paging Channel message

Fixed data rate (4800 bps) & 20 ms frame duration

•Access Channel Message may carry

•Origination of a call • Paging responses

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Access

Channel

•Origination of a call • Paging responses

•Orders response • Data bursts

•Acknowledgements to Paging Channel message

•Registration

Information Bits = 88 bitsEncoder Tail

8 bits

96 bits (20 ms)

•Basic frame structure

Access Channel Frame Structure

• Access channel message has length of 88 x N bits

Message

Length

(in bytes)

8 bits

Data

N MSG = 2 ~ 842 bits

CRC

16 bits

Padding

= …000...

Chung-Wei Ku

ATC/CCL/ITRI


• Access channel slot is as

– Access channel frame = 88-bits + 8-bit tail bits (all 0s)

– The value of PAM_SZ and MAX_CAP_SZ are received on the paging

channel

Access Channel Preamble = 000…000

96 x (1+PAM_SZ) bits

Access Channel Frame

96 bits

... Access Channel Frame

96 bits

96 x (4+PAM_SZ+MAX_CAP_SZ) bits

Access Channel Slot Structure

Is (3+MAX_CAP_SZ)+(1+PAM_SZ) Access Channel frames in length

•An Access Channel slot begins & ends on an Access Channel frame

boundary.

•Access Channel slots begin at Access Channel frames in which

t mod (4+MAX_CAP_SZ+PAM_SZ)=0 & t: system time in frames

Chung-Wei Ku

ATC/CCL/ITRI


Access Channel

Slot Structure

t mod (4+MAX_CAP_SZ+PAM_SZ)=0 & t: system time in frames

Preamble Max Capsule Size

Access Transmission

Max Length

Access Slot

Boundary20 ms

Access channel frame

Access channel slot of five

20 ms Access Channel frames

Access Slot n Access Slot n+1 Access Slot n+2

Access Channel Structure

Access Channel Slot

ACFrame

ACFrame

ACFrame

ACFrame

ACFrame

Nf frames=96 × Nf bits1+ PAM_SZ frame=96 × (1+ PAM_SZ)bits

20 ms = 96 bits

0.02 × (4+PAM_SZ+MAX_CAP_SZ) sec = 96 × (4+PAM_SZ+MAX_CAP_SZ) bits

Chung-Wei Ku

ATC/CCL/ITRI


Access Channel PreambleAC

BodyAC

BodyAC

BodyT T T

Access Channel Message Capsule

Access Channel Message Padding

MSGLength

Message Body CRC

8 bits 2~842 bits 30 bits

8× MSG_Length bits As Required

88 × Nf bits

Nf frames=96 × Nf bits1+ PAM_SZ frame=96 × (1+ PAM_SZ)bits

AC frame = Access Channel frame

Nf :: Number of Access Channel frames

needed for message transmission

T :: Encoder Tail bits

Access Channel field (MSG_Length & CRC)

Access Channel field

(MSG_Length & CRC)



Message Body CRC



MSGLength

Chung-Wei Ku

ATC/CCL/ITRI


Length

•The MS set the field of to the length of the message in octets, including

the MSG_Length, the message body & the CRC.

•The field shall be 8 bits in length, & the MS shall limit the maximum

Access Channel length to 110 octets or 880 bits

• The CRC includes the MSG_Length & the message body.

The generator polynomial for the CRC is::g(x)=X30+X29+X21+X20+X15+X13+X12+X11+X8+X7+X6+X2+1

Access Channel field (Message Body)


(Message Body)



Message Body CRC



MSGLength

Chung-Wei Ku

ATC/CCL/ITRI


Length

Message TypeCommon Layer 2 &

Identification field

Common Authentication

field

Reserved or others

as needed

•Registration Message = “00000001”•Order Message = “00000010”•Data Burst Message = “00000011”•Origination Message = “00000110”•Page Response Message = “00000101”•Authentication Challenge Response Message = “00000110”



(Message Body)



Message Body CRC



MSGLength

Chung-Wei Ku

ATC/CCL/ITRI


Length




field

Reserved or others

as needed

•ACK_SEQ:: Acknowledgement Sequence Number • MSG_SEQ:: Message Sequence Number•ACK_REQ:: Acknowledgement Required Indicator • VALID_ACK:: Valid Acknowledgement Indicator•ACK_TYPE:: Acknowledgement Address Type • MSID_TYPE:: MS Identifier field type•MSID_LEN:: MS Identifier field length • MSID:: MS Identifier

8 fields



(Message Body)



Message Body CRC



MSGLength

Chung-Wei Ku

ATC/CCL/ITRI


Length




field

Reserved or others

as needed

AUTH_MODE: Authentication mode

AUTHR: Authentication data

RANDC: Random Challenge value

COUNT: Call history parameter

4 fields

Access Channel field: Registration Message


Registration

Message



Message Body CRC



MSGLength

REG_TYPE

(4 bits)

SLOT_CYCLE

INDEX(3 bits)

MOB_P_REV

(8 bits)

SCM

(8 bits)

MOB_TERM

(1 bits)

Reserved

(6 bits)

Chung-Wei Ku

ATC/CCL/ITRI


Length




field

Reserved or others

as needed

00000001

Registration MessageRegistration Message

ACK_SEQ

(3 bits)

MSG_SEQ

(3 bits)

ACK_REQ

(1 bits)

VALID_ACK

(1 bits)

ACK_TYPE

(3 bits)

MSID_TYPE

(3 bits)

MSID_LEN

(4 bits)

MSID

(8×MSID_LEN)

AUTH_MODE

(2 bits)

AUTHR

(0 or 18 bits)

RANDC

(0 or 8 bits)

COUNT

(0 or 6 bits)

Access Channel field: Order Message


Order Message



Message Body CRC



MSGLength

Reversed

(2 bits)

Order

(6 bits)

ADDR_

RECORD_LEN

(3 bits)

Order-specific

field if used

(8 × Add_record_len bits)

Reserved

(5 bits)

Chung-Wei Ku

ATC/CCL/ITRI


Message Body CRCLength




field

Reserved or others

as needed

00000010

Order MessageOrder Message

ACK_SEQ

(3 bits)

MSG_SEQ

(3 bits)

ACK_REQ

(1 bits)

VALID_ACK

(1 bits)

ACK_TYPE

(3 bits)

MSID_TYPE

(3 bits)

MSID_LEN

(4 bits)

MSID

(8×MSID_LEN)

(3 bits) (8 × Add_record_len bits)

Does NOT have This Field

Access Channel field: Data Burst Message


Data Burst Message



Message Body CRC



MSGLength

MSG_

NUMBERBurst_TYPE NUM_MSGS SNUM_FIELD CHARi

Chung-Wei Ku

ATC/CCL/ITRI


Length




field

Reserved or others

as needed

00000011

Data Burst MessageData Burst Message

ACK_SEQ

(3 bits)

MSG_SEQ

(3 bits)

ACK_REQ

(1 bits)

VALID_ACK

(1 bits)

ACK_TYPE

(3 bits)

MSID_TYPE

(3 bits)

MSID_LEN

(4 bits)

MSID

(8×MSID_LEN)

AUTH_MODE

(2 bits)

AUTHR

(0 or 18 bits)

RANDC

(0 or 8 bits)

COUNT

(0 or 6 bits)

NUMBER

(8 bits)

Burst_TYPE

(6 bits)

NUM_MSGS

(8 bits)

SNUM_FIELD

(8 bits)

CHARi

(8 bits)

Access Channel field: Origination Message


Origination Message



Message Body CRC



MSGLength

1

(1 b

its)

2

(3 b

its)

3

(8 b

its)

4

(8 b

its)

5

(3 b

its)

6

(1 b

its)

7

(0 o

r 1

6 b

its)

8

(1 b

its)

9

(1 b

its)

10

(0 o

3 b

its)

11

(0 o

r 4

bit

s)1

2

(1 b

its)

13

(8 b

its)

14

(4 o

r 8

bit

s)1

5

(1 b

its)

16

(0~

7 b

its)

Chung-Wei Ku

ATC/CCL/ITRI


Length




field

Reserved or others

as needed

00000100

Origination MessageOrigination Message

ACK_SEQ

(3 bits)

MSG_SEQ

(3 bits)

ACK_REQ

(1 bits)

VALID_ACK

(1 bits)

ACK_TYPE

(3 bits)

MSID_TYPE

(3 bits)

MSID_LEN

(4 bits)

MSID

(8×MSID_LEN)

AUTH_MODE

(2 bits)

AUTHR

(0 or 18 bits)

RANDC

(0 or 8 bits)

COUNT

(0 or 6 bits)

(0 o

r 1

6 b

its)

(0 o

3 b

its)

(0 o

r 4

bit

s)

(4 o

r 8

bit

s)

(0~

7 b

its)

1:: MOB_TERM 2::SLOT_CYCLE_INDEX 3::MOB_P_REV 4::SCM 5::REQUEST_MODE 6::SPECIAL_SERVICE 7::SERVICE_OPATION 8::PM

9:DIGIT_MODE 10::NUMBER_TYPE 11::NUMBER_PLAN 12::MORE_FIELDS 13::NUM_FIELDS 14::CHARi 15::NAR_AN_CAP 16::RESERVED

NUM_FIELDS occurrences of this field

Access Channel field: Page Response Message


Page Response

Message



Message Body CRC



MSGLength M

OB

_

TE

RM

(1 b

its)

SL

OT

_C

YC

LE

IND

EX

(3 b

its)

MO

B_

P_

RE

V

(8 b

its)

SC

M

(8 b

its)

RE

QU

ES

T_

MO

DE

(3 b

its)

SE

RV

ICE

_

OP

TIO

N

(16

b

its)

PM

(1 b

its)

NA

R_

AN

_C

AP

(1 b

its)

RE

SE

RV

ED

(5 b

its)

Chung-Wei Ku

ATC/CCL/ITRI


Message Body CRCLength




field

Reserved or others

as needed

00000101

Page Response MessagePage Response Message

ACK_SEQ

(3 bits)

MSG_SEQ

(3 bits)

ACK_REQ

(1 bits)

VALID_ACK

(1 bits)

ACK_TYPE

(3 bits)

MSID_TYPE

(3 bits)

MSID_LEN

(4 bits)

MSID

(8×MSID_LEN)

AUTH_MODE

(2 bits)

AUTHR

(0 or 18 bits)

RANDC

(0 or 8 bits)

COUNT

(0 or 6 bits)

MO

B_

TE

RM

(1 b

its)

SL

OT

_C

YC

LE

IND

EX

(3 b

its)

MO

B_

P_

RE

V

(8 b

its)

SC

M

(8 b

its)

RE

QU

ES

T_

MO

DE

(3 b

its)

SE

RV

ICE

_

OP

TIO

N

(16

b

its)

(1 b

its)

NA

R_

AN

_C

AP

(1 b

its)

RE

SE

RV

ED

(5 b

its)

Access Channel field:

Authentication Challenge Response Message


Authentication Challenge

Response Message



Message Body CRC



MSGLength

RESERVED

(4 bits)

Chung-Wei Ku

ATC/CCL/ITRI


Length




field

Reserved or others

as needed

00000110

Authentication Challenge Response MessageAuthentication Challenge Response Message

ACK_SEQ

(3 bits)

MSG_SEQ

(3 bits)

ACK_REQ

(1 bits)

VALID_ACK

(1 bits)

ACK_TYPE

(3 bits)

MSID_TYPE

(3 bits)

MSID_LEN

(4 bits)

MSID

(8×MSID_LEN)

RESERVED

(2 bits)

AUTHR

(0 or 18 bits)

(4 bits)

Reverse Traffic Channels

• Variable data rates and format are as forward traffic channel. But transmission duty

cycle is reduced accordingly. (Bits are not repeated on this channel.)

• Message format is identical to the forward traffic channel.

Reverse Traffic

Channel

Information Bits

Convolutional

EncoderSymbol

Repetition

Add Frame

Quality Indicator

for 9600 &

Add 8-bit

Encoder

Code

Symbol

Chung-Wei Ku

ATC/CCL/ITRI


Information Bits

(172, 80, 40 or

16 bits/frame)

8.6 kbps

4.0 kbps

2.0 kbps

0.8 kbps

Encoder

R=1/3, K=9Repetition

Block

Interleaver

Code

Symbol

28.8 ksps

Code

Symbol

28.8 ksps

for 9600 &

4800 bps Rates

Encoder

Tail9.2 kbps

4.4 kbps

2.0 kbps

0.8 kbps

9.6 kbps

4.8 kbps

2.4 kbps

1.2 kbps

28.8 ksps

14.4 ksps

7.2 ksps

3.6 ksps

Long Code

MaskLong Code

Generator

PN Chips

1.2288 Mcps64-ary

Orthogonal

Modulator

Modulation

Symbol

(Walsh chip)

4.8 ksps

(307.2 kcps)

Data Burst

Randomizer

Frame Data Rate

Reverse CDMA Channel Signal Generation

Chung-Wei Ku

ATC/CCL/ITRI


Reverse Channel Modulator (Spreading)

• Identical I, Q signals; but different I, Q PN sequences (long code

+ short code)

• OQPSK modulation

Chung-Wei Ku

ATC/CCL/ITRI


Reverse Link Modulation Parameters

• 20 ms interleaver for time diversity

• Orthogonal 64-ary Walsh modulation symbols

• Long code of period 2 42 -1 (for channel identification)

concatenated with PN codes of length 2 15.

• Noncoherent OQPSK

Chung-Wei Ku

ATC/CCL/ITRI


• Noncoherent OQPSK

• Diversity

– time diversity: coding + interleaving

– path diversity: RAKE receiver

– spatial diversity: 2 Rx antennas (4 Rx antennas available during handoff)

Reverse Channel Demodulation

• System with 4 fingers and 8 searchers

Antenna BAntenna A

Chung-Wei Ku

ATC/CCL/ITRI


Nocoherent Maximal Ratio Combining

Soft Decisions to Viterbi Decoder

Signaling Flow of Registration Process

• MS notifies BS of its presence (location, status, identification,

etc.) in the system

• IS-95 supports the following registration types:

– power-up registration

– power-down registration

Chung-Wei Ku

ATC/CCL/ITRI


– power-down registration

– timer-based registration

– distance-based registration

– zone-based registration

– parameter-change registration

– ordered registration

– implicit registration

Signaling Flow of Registration Process

MS BS MSCNew

VLR

Old

VLRHLR

Register Determination

Global Challenge

Register

Validate RAND

Chung-Wei Ku

ATC/CCL/ITRI


Validate RAND

ISDN REGISTERREGISTER

IS-41 REGNOT

Database Update

IS-41 REGCANC

ConfirmREGNOT ResponseREGISTER

ResponseISDN

REGISTER

Register Confirm

Initialization and Call Processing of MS

• Acquires the pilot channel

• Receives the sync channel with sync channel message

• Adjust to system timing

• Receives the paging channel message

Chung-Wei Ku

ATC/CCL/ITRI


• Sends origination message (also registration) on the access

channel

• Receives channel assignment message on the paging channel

• Initializes the traffic channel

• Enters conversion substate

an introduction to cdma air interface

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