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CDMA Technology Overview

CDMA Technology Overview. Lesson 4 - CDMA Reverse Channels. Access Channels. Code Channels in the Reverse Direction. BTS. REG. 1-800 242 4444. There are two types of CDMA Reverse Channels:

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CDMA Technology Overview

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  1. CDMA Technology Overview Lesson 4 - CDMA Reverse Channels

  2. Access Channels

  3. Code Channels in the Reverse Direction BTS REG 1-800 242 4444 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 asthere 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

  4. Coding Process in the Reverse Direction MTX BSC BTS (1 sector) Long Code Gen Access Channels Channel Element User Long Code Long Code Gen Vocoder Channel Element User Long Code Receiver, Sector X Long Code Gen Vocoder Channel Element Long Code Gen User Long Code User Long Code Vocoder Channel Element User Long Code User Long Code Long Code Gen Vocoder Channel Element more more more A Reverse Channel is identified by: • its CDMA RF carrierFrequency • the uniqueLong Code PN Offsetof the individual handset CDMA Frequency

  5. Access Channels 4800 bps • 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

  6. Access Channel Generation IPN (No Offset) R = 1/3 Access Channel Information (88 bits/Frame) 1.2288 Mcps 28.8 ksps 28.8 ksps 307.2 kcps Orthogonal Modulation Convolutional Encoder & Repetition Block Interleaver 1/2 PN Chip Delay 4.8 kpbs D 1.2288 Mcps Long PN CodeGenerator Access ChannelLong Code Mask Q PN (No Offset) Direct Sequence Spreading • 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)

  7. Rate 1/3 Convolutional Encoder Code Symbols (OUTPUT) g0 + Information bits (INPUT) 1 2 3 4 5 6 7 8 + Code Symbols (OUTPUT) g1 + Code Symbols (OUTPUT) g2

  8. Access Channel Block Interleaving Input Array (Normal Sequence) 32 x 18 Output Array (Reordered Sequence) 32 x 18 28.8 ksps from Conv. Encoding & Symbol Repetition (2x) 28.8 ksps to Orthogonal Modulation • 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

  9. 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 89 105 121 137 153 169 185 201 217 233 249 265 281 10 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250 266 282 10 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250 266 282 11 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251 267 283 11 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251 267 283 12 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252 268 284 12 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252 268 284 13 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253 269 285 13 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253 269 285 14 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254 270 286 14 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254 270 286 15 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255 271 287 15 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255 271 287 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288

  10. 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 85 101 117 133 149 165 181 197 213 229 245 261 277 13 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253 269 285 3 19 35 51 67 83 99 115 131 147 163 179 195 211 227 243 259 275 11 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251 267 283 7 23 39 55 71 87 103 119 135 151 167 183 199 215 231 247 263 279 15 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255 271 287 2 18 34 50 66 82 98 114 130 146 162 178 194 210 226 242 258 274 10 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250 266 282 6 22 38 54 70 86 102 118 134 150 166 182 198 214 230 246 262 278 14 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254 270 286 4 20 36 52 68 84 100 116 132 148 164 180 196 212 228 244 260 276 12 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252 268 284 8 24 40 56 72 88 104 120 136 152 168 184 200 216 232 248 264 280 16 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 85 101 117 133 149 165 181 197 213 229 245 261 277 13 29 45 61 77 93 109 125 141 157 173 189 205 221 237 253 269 285 3 19 35 51 67 83 99 115 131 147 163 179 195 211 227 243 259 275 11 27 43 59 75 91 107 123 139 155 171 187 203 219 235 251 267 283 7 23 39 55 71 87 103 119 135 151 167 183 199 215 231 247 263 279 15 31 47 63 79 95 111 127 143 159 175 191 207 223 239 255 271 287 2 18 34 50 66 82 98 114 130 146 162 178 194 210 226 242 258 274 10 26 42 58 74 90 106 122 138 154 170 186 202 218 234 250 266 282 6 22 38 54 70 86 102 118 134 150 166 182 198 214 230 246 262 278 14 30 46 62 78 94 110 126 142 158 174 190 206 222 238 254 270 286 4 20 36 52 68 84 100 116 132 148 164 180 196 212 228 244 260 276 12 28 44 60 76 92 108 124 140 156 172 188 204 220 236 252 268 284 8 24 40 56 72 88 104 120 136 152 168 184 200 216 232 248 264 280 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256 272 288

  11. Access Channel Structure 4800 bps 20 x (4 + PAM_SZ + MAX_CAP_SZ) ms 96 x (4 + PAM_SZ + MAX_CAP_SZ) bits Access Channel Slot 20 ms 96 bits 96 x Nf bits (not exceeding 3 + MAX_CAP_SZ frames) Access Channel Frame Access Channel Frame Body Access Channel Preamble T T T T 1 + PAM_SZ frames 96 x (1 + PAM_SZ) bits Access Channel Message Capsule 88 x Nf bits Nf = Number of Access Channel Frames needed for message transmission T = Encoder Tail Bits(eight zeroes) Access Channel Message Padding as required 8 x MSG_LENGTH Message Body MSG_LENGTH CRC 8 bits 2-842 bits 30 bits

  12. Access Channel Probing Access Probe 1 + NUM_STEP (16 max) Access Probe 1 PI ACCESS PROBE SEQUENCE Access Probe 1 PI Access Probe 1 PI Access Probe 1 IP (Initial Power) System Time TA RT TA RT TA RT TA Select Access Channel (RA) initialize transmit power See previous figure

  13. Reverse Traffic Channels

  14. 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

  15. Reverse Traffic Channel Generation IPN (no offset) 9600 bps 4800 bps 2400 bps 1200 bps or 14400 bps 7200 bps 3600 bps 1800 bps R = 1/3 1.2288 Mcps 28.8 ksps 28.8 ksps 307.2 kcps Orthogonal Modulation Convolutional Encoder & Repetition 1/2 PN Chip Delay Data Burst Randomizer Block Interleaver D R = 1/2 1.2288 Mcps Q PN (no offset) Long PN Code Generator User AddressMask Direct Sequence Spreading

  16. Reverse Traffic Channel Frame Structure Rate Set Transmission Rate Number of Bits per Frame Total Information CRC Tail Bits Erasure 1 9600 192 — 172 12 8 4800 96 — 80 8 8 2400 48 — 40 — 8 1200 24 — 16 — 8 2 14400 288 1 267 12 8 7200 144 1 125 10 8 3600 72 1 55 8 8 1800 36 1 21 6 8

  17. Reverse Traffic Channel Convolutional Encoding & Symbol Repetition 9.6 kbps 4.8 kbps 2.4 kbps 1.2 kbps 28.8 ksps (No repetition) 14.4 ksps (2 X repetition) 7.2 ksps (4 X repetition) 3.6 ksps (8 X repetition) PCM Voice Vocoder Processing Variable Rate Output from Vocoder R=1/3K=9 Convolutional Encoder R=1/2K=9 Symbol Repetition Convolutional Encoding 28.8 ksps to Block Interleaver Code Symbol Repetition Block Interleaving 14.4 kbps 7.2 kbps 3.6 kbps 1.8 kbps 28.8 ksps (No repetition) 14.4 ksps (2 X repetition) 7.2 ksps (4 X repetition) 3.6 ksps (8 X repetition) Orthogonal Modulation Data Burst Randomizer Direct Sequence Spreading Quadrature Spreading Baseband Filtering Baseband Traffic to RF Section • 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

  18. Reverse Traffic Channel Block Interleaving PCM Voice Input Array (Normal Sequence) 32 x 18 Output Array (Reordered Sequence) 32 x 18 Vocoder Processing 28.8 ksps From Coding & Symbol Repetition 28.8 ksps to Orthogonal Modulation Convolutional Encoding Code Symbol Repetition Block Interleaving Orthogonal Modulation Data Burst Randomizer Direct Sequence Spreading Quadrature Spreading Baseband Filtering Baseband Traffic to RF Section • 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

  19. Lesson Review • The two types of CDMA Reverse Channels are Traffic Channels and Access Channels. [True/False] True • Short PN sequences are used to achieve _____________________. Phase Modulation • How many access channels are supported by a single paging channel? 32 (0 - 31) • When generating the Access Channel, why are message attempts randomized? To reduce the probability of collision • What is the access channel preamble? A frame comprised of 96 zeroes that aids the base station in acquiring access channel transmission.

  20. Lesson Review, cont’d • 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 • 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 • 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. • What is used in the reverse path: direct sequence spreading or data scrambling? Direct sequence spreading

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