Download - CDMA Technology OverviewFebruary, 2001 - Page 3-1 CDMA Technology Overview Lesson 4 - CDMA Reverse Channels.

CDMA Technology Overview February, 2001 - Page 3-1

CDMA Technology CDMA Technology OverviewOverview

Lesson 4 - CDMA Reverse Channels


Access Channels


REG

1-800242

4444

BTS

Code Channels in the Reverse Direction

There are two types of CDMA Reverse Channels:

TRAFFIC CHANNELS are used by individualusers during their actual calls to transmit trafficto the BTS a reverse traffic channel is defined by a user-specific

public or private Long Code mask there are as many reverse Traffic Channels as

there are CDMA phones in the world

ACCESS CHANNELS are used by mobile stations not yet in a call to transmit registration requests, call setup requests, page responses, order responses, and other signaling information an access channel is defined by a user-independent

public long code mask Access channels are paired with Paging Channels.

There can be up to 32 access channels per paging channel


MTX BSC BTS (1 sector)

Channel Element

Access Channels

Vocoder

Vocoder

Vocoder

Vocoder

more more

Receiver,Sector X

Channel Element

Channel Element

Channel Element

Channel Element

Long Code Gen

Long Code Gen

Long Code Gen

Long Code Gen

Long Code Gen

more

UserLongCode User

LongCode User

LongCode

UserLongCode

UserLongCode

UserLongCode

Coding Process in the Reverse Direction

A Reverse Channel is identified by: its CDMA RF carrier Frequency the unique Long Code PN Offset

of the individual handset

CDMAFrequency


Access Channels

Used by the mobile station to Initiate communication with the base station Respond to Paging Channel messages

Has a fixed data rate of 4800 bps Each Access Channel is associated with only one Paging Channel Up to 32 access channels (0-31) are supported per Paging Channel

4800 bps


Access Channel Generation

Message attempts are randomized to reduce probability of collision Two message types:

A response message (in response to a base station message) A request message (sent autonomously by the mobile station)

28.8kspsConvolutional

Encoder &Repetition

R = 1/3

1.2288McpsAccess Channel

Long Code MaskLong PN Code

Generator

28.8ksps Orthogonal

Modulation

307.2kcps

1.2288Mcps

Q PN (No Offset)

I PN (No Offset)

D

1/2 PNChipDelay

BlockInterleaver

Access ChannelInformation

(88 bits/Frame)

4.8 kpbs

DirectSequenceSpreading


Rate 1/3 Convolutional Encoder

+

+

+

g0

g1

g2

Information bits(INPUT)

Code Symbols(OUTPUT)



1 2 3 4 5 6 7 8


Access Channel Block Interleaving

576 code symbols (288 x 2) are written sequentially by columns, then read by rows in a particular order (called “bit-reverse readout of the row addresses”) every 20 ms

Block interleaving separates repeated symbols in two identical sets: one set is transmitted during the first 10 ms and the second set, with the repetitions, is transmitted during the second 10 ms Improves survivability of symbol information “Spreads” the effect of spurious interference and fast fading

28.8 ksps fromConv. Encoding

& SymbolRepetition (2x)

Input Array(Normal

Sequence)32 x 18

Output Array(ReorderedSequence)

32 x 18

28.8 ksps toOrthogonalModulation


Access Channel Block Interleaving(4800 x 2 bps - Write Matrix)

1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 241 257 273 1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 241 257 273 2 18 34 50 66 82 98 114 130 146 162 178 194 210 226 242 258 274 2 18 34 50 66 82 98 114 130 146 162 178 194 210 226 242 258 274 3 19 35 51 67 83 99 115 131 147 163 179 195 211 227 243 259 275 3 19 35 51 67 83 99 115 131 147 163 179 195 211 227 243 259 275 4 20 36 52 68 84 100 116 132 148 164 180 196 212 228 244 260 276 4 20 36 52 68 84 100 116 132 148 164 180 196 212 228 244 260 276 5 21 37 53 69 85 101 117 133 149 165 181 197 213 229 245 261 277 5 21 37 53 69 85 101 117 133 149 165 181 197 213 229 245 261 277 6 22 38 54 70 86 102 118 134 150 166 182 198 214 230 246 262 278 6 22 38 54 70 86 102 118 134 150 166 182 198 214 230 246 262 278 7 23 39 55 71 87 103 119 135 151 167 183 199 215 231 247 263 279 7 23 39 55 71 87 103 119 135 151 167 183 199 215 231 247 263 279 8 24 40 56 72 88 104 120 136 152 168 184 200 216 232 248 264 280 8 24 40 56 72 88 104 120 136 152 168 184 200 216 232 248 264 280 9 25 41 57 73 89 105 121 137 153 169 185 201 217 233 249 265 281 9 25 41 57 73 89 105 121 137 153 169 185 201 217 233 249 265 28110 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250 266 28210 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250 266 28211 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251 267 28311 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251 267 28312 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252 268 28412 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252 268 28413 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253 269 28513 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253 269 28514 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254 270 28614 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254 270 28615 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255 271 28715 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255 271 28716 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 28816 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288


Access Channel Block Interleaving(4800 x 2 bps - Read Matrix)

1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 241 257 273 9 25 41 57 73 89 105 121 137 153 169 185 201 217 233 249 265 281 5 21 37 53 69 85 101 117 133 149 165 181 197 213 229 245 261 27713 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253 269 285 3 19 35 51 67 83 99 115 131 147 163 179 195 211 227 243 259 27511 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251 267 283 7 23 39 55 71 87 103 119 135 151 167 183 199 215 231 247 263 27915 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255 271 287 2 18 34 50 66 82 98 114 130 146 162 178 194 210 226 242 258 27410 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250 266 282 6 22 38 54 70 86 102 118 134 150 166 182 198 214 230 246 262 27814 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254 270 286 4 20 36 52 68 84 100 116 132 148 164 180 196 212 228 244 260 27612 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252 268 284 8 24 40 56 72 88 104 120 136 152 168 184 200 216 232 248 264 28016 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288

1 17 33 49 65 81 97 113 129 145 161 177 193 209 225 241 257 273 9 25 41 57 73 89 105 121 137 153 169 185 201 217 233 249 265 281 5 21 37 53 69 85 101 117 133 149 165 181 197 213 229 245 261 27713 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253 269 285 3 19 35 51 67 83 99 115 131 147 163 179 195 211 227 243 259 27511 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251 267 283 7 23 39 55 71 87 103 119 135 151 167 183 199 215 231 247 263 27915 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255 271 287 2 18 34 50 66 82 98 114 130 146 162 178 194 210 226 242 258 27410 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250 266 282 6 22 38 54 70 86 102 118 134 150 166 182 198 214 230 246 262 27814 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254 270 286 4 20 36 52 68 84 100 116 132 148 164 180 196 212 228 244 260 27612 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252 268 284 8 24 40 56 72 88 104 120 136 152 168 184 200 216 232 248 264 28016 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288


Access Channel Structure

Access Channel Message Padding

CRC

20 ms

96 bits

8 x

MSG_LENGTH

8 bits 30 bits

MSG_LENGTH

2-842 bits

as

required

Access Channel Frame

Message Body

20 x (4 + PAM_SZ + MAX_CAP_SZ) ms96 x (4 + PAM_SZ + MAX_CAP_SZ) bits

4800 bps

Nf =Number of AccessChannel Frames

needed for message transmissionT = Encoder Tail Bits

(eight zeroes)

Access Channel Frame Body

1 + PAM_SZ frames96 x (1 + PAM_SZ) bits

96 x Nf bits (not exceeding 3 + MAX_CAP_SZ frames)

Access Channel Slot

TAccess Channel Preamble

Access Channel Message Capsule

T TT

88 x Nf bits


Access Channel Probing

AccessProbe 1

AccessProbe 1

AccessProbe 1

AccessProbe 1

Access Probe1 + NUM_STEP

(16 max)

SystemTime

TA RT TA RT TA RT TA

PI

PI

PI

IP(InitialPower)

See previousfigure

ACCESSPROBE

SEQUENCE

Select Access Channel (RA)initialize transmit power


Reverse Traffic Channels


CDMA Reverse Traffic Channels

Used when a call is in progress to send Voice traffic from the subscriber Response to commands/queries from the base station Requests to the base station

Supports variable data rate operation for 8 Kbps vocoder

Rate Set 1 - 9600, 4800, 2400 and 1200 bps Multiplex Option 1

13 Kbps vocoder Rate Set 2 - 14400, 7200, 3600, 1800 bps Multiplex Option 2


Reverse Traffic Channel Generation

9600 bps4800 bps2400 bps1200 bps

or

14400 bps7200 bps3600 bps1800 bps

28.8ksps

R = 1/3

1.2288McpsUser Address

MaskLong

PN CodeGenerator

28.8ksps Orthogonal

Modulation

Data BurstRandomizer

307.2kcps

1.2288Mcps

Q PN(no offset)

I PN(no offset)

D

1/2 PNChipDelay

DirectSequenceSpreading

R = 1/2

ConvolutionalEncoder &Repetition

BlockInterleaver


Reverse Traffic Channel Frame Structure

TransmissionRate Total Erasure Information CRC Tail Bits

9600 192 — 172 12 8

4800 96 — 80 8 8

2400 48 — 40 — 8

1200 24 — 16 — 8

14400 288 1 267 12 8

7200 144 1 125 10 8

3600 72 1 55 8 8

1800 36 1 21 6 8

1

2

Number of Bits per FrameRateSet


Reverse Traffic Channel Convolutional Encoding & Symbol Repetition

Convolutional encoding: Results in 3 code symbols out for each bit in, at Rate Set

1, and in 2 code symbols out for each bit in, at Rate Set 2 Also allows for reduction in transmit power Reduces overall noise & increases capacity

Symbol repetition maintains a constant 28.8 ksps output to block interleaver

PCM Voice

ConvolutionalEncoding

Code SymbolRepetition

BlockInterleavingOrthogonalModulationData Burst

RandomizerDirect Sequence

SpreadingQuadratureSpreadingBasebandFiltering

VocoderProcessing

Baseband Traffic to RF Section

VariableRate

Outputfrom

Vocoder

R=1/3 K=9 Convolutional

EncoderR=1/2 K=9

28.8 kspsto Block

Interleaver

28.8 ksps (No repetition)14.4 ksps (2 X repetition)

7.2 ksps (4 X repetition)3.6 ksps (8 X repetition)

28.8 ksps (No repetition)14.4 ksps (2 X repetition)

7.2 ksps (4 X repetition)3.6 ksps (8 X repetition)

SymbolRepetition

9.6 kbps4.8 kbps2.4 kbps1.2 kbps

14.4 kbps 7.2 kbps 3.6 kbps 1.8 kbps


Reverse Traffic Channel Block Interleaving

20 ms symbol blocks are sequentially reordered Combats the effects of fast fading Separates repeated symbols at 4800 bps and

below Improves survivability of symbol data “Spreads” the effect of spurious interference

PCM Voice

ConvolutionalEncoding

Code SymbolRepetition

BlockInterleaving

VocoderProcessing

Baseband Traffic to RF Section

OrthogonalModulationData Burst

RandomizerDirect Sequence

SpreadingQuadratureSpreadingBasebandFiltering

28.8 kspsFrom Coding& SymbolRepetition

Output Array(ReorderedSequence)

32 x 18

28.8 ksps toOrthogonalModulation

Input Array(Normal

Sequence)32 x 18


Lesson Review

1. The two types of CDMA Reverse Channels are Traffic Channels and Access Channels. [True/False]

True

2. Short PN sequences are used to achieve _____________________.

Phase Modulation

3. How many access channels are supported by a single paging channel?

32 (0 - 31)

4. When generating the Access Channel, why are message attempts randomized?

To reduce the probability of collision

5. What is the access channel preamble?

A frame comprised of 96 zeroes that aids the base station in acquiring access channel transmission.


Lesson Review, cont’d

6. All Access Channels associated with a particular Paging Channel

a. have the same slot size

b. do not have the same slot size

c. all slots begin at the same time

d. all slots do not begin at the same time

e. a and c

f. a and d

g. none of the above

a and c

7. Why is the Reverse Traffic Channel preamble transmitted by the mobile to the base station?

To help the base station acquire the Reverse Traffic Channel

8. The pilot PN sequences are offset relative to system time, not mobile station time. Why?

The mobile draws its time reference from the earliest usable pilot component it receives.

9. What is used in the reverse path: direct sequence spreading or data scrambling?

Direct sequence spreading
