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CDMA Technology Overview February, 2001 - Page 3-1
CDMA Technology CDMA Technology OverviewOverview
Lesson 4 - CDMA Reverse Channels
CDMA Technology Overview February, 2001 - Page 3-2
Access Channels
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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
CDMA Technology Overview February, 2001 - Page 3-4
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
CDMA Technology Overview February, 2001 - Page 3-5
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
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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
CDMA Technology Overview February, 2001 - Page 3-7
Rate 1/3 Convolutional Encoder
+
+
+
g0
g1
g2
Information bits(INPUT)
Code Symbols(OUTPUT)
Code Symbols(OUTPUT)
Code Symbols(OUTPUT)
1 2 3 4 5 6 7 8
CDMA Technology Overview February, 2001 - Page 3-8
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
CDMA Technology Overview February, 2001 - Page 3-9
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 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
CDMA Technology Overview February, 2001 - Page 3-10
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 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
CDMA Technology Overview February, 2001 - Page 3-11
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
CDMA Technology Overview February, 2001 - Page 3-12
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
CDMA Technology Overview February, 2001 - Page 3-13
Reverse Traffic Channels
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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
CDMA Technology Overview February, 2001 - Page 3-15
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
CDMA Technology Overview February, 2001 - Page 3-16
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
CDMA Technology Overview February, 2001 - Page 3-17
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
CDMA Technology Overview February, 2001 - Page 3-18
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
CDMA Technology Overview February, 2001 - Page 3-19
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.
CDMA Technology Overview February, 2001 - Page 3-20
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
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