北电CDMA技术原理Lesson.ppt

1、CDMA Technology Overview,Lesson 4 - CDMA Reverse Channels,Access Channels,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

2、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

3、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,Coding Process in the Reverse Direction,A Reverse Channel is identified by: its CDMA RF carrier Frequency the

4、 unique Long Code PN Offset of the individual handset,CDMA Frequency,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

5、 access channels (0-31) are supported per Paging Channel,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),Rate 1/3 Con

6、volutional Encoder,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

7、 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,Access Channel Block Interleaving(4800 x 2 bps - Write Matrix),1 17 33 49 65

8、 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 2

9、59 275 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 1

10、65 181 197 213 229 245 261 277 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 5

11、6 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

12、 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 1

13、08 124 140 156 172 188 204 220 236 252 268 284 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 2

14、54 270 286 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,Access Channel Block Inte

15、rleaving(4800 x 2 bps - Read Matrix),Access Channel Structure,Access Channel Probing,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 Suppor

16、ts 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,Reverse Traffic Channel Frame Structure,Reverse Traffic Channel Convolutiona

17、l 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

18、28.8 ksps output to block interleaver,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,Less

19、on 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.,Lesson Review, contd,All Access Channels associated w