CDMA Technology Overview

CDMA Technology Overview February, 2001 - Page 2-1

CDMA Technology Overview

Lesson 3 - Forward Traffic Channels


CDMA Forward Traffic Channels

Used for the transmission of user and signaling information to a specific mobile station during a call

Maximum number of traffic channels: 64 minus one Pilot channel, one Sync channel, and 1 to 7 Paging channels This leaves each CDMA frequency with at least 55 traffic channels Unused paging channels can provide up to 6 additional channels Realistic loading will typically be about 17 subscribers when using

the 13 kb vocoder (22 when using the 8 kb vocoder)

Forward Traffic Channel

Sync

Paging



Pilot

CDMA Cell Site


Pilot Walsh 0

Walsh 19

Paging Walsh 1Walsh 6

Walsh 11

Walsh 20Sync Walsh 32

Walsh 42

Walsh 37Walsh 41

Walsh 56Walsh 60

Walsh 55

Code Channels in the Forward Direction

PILOT: WALSH CODE 0The Pilot is a “structural beacon” which does not contain a character stream. It is a timing source used in system acquisition and as a measurement device during handoffs

SYNC: WALSH CODE 32This carries a data stream of system identification and parameter information used by mobiles during system acquisition

PAGING: WALSH CODES 1 up to 7There can be from one to seven paging channels as determined by capacity needs. They carry pages, system parameters information, and call setup orders

TRAFFIC: any remaining WALSH codesThe traffic channels are assigned to individual users to carry call traffic. All remaining Walsh codes are available, subject to overall capacity limited by noise


BTS (1 sector)MTX BSC

FECWalsh #1

Sync FECWalsh #32

Walsh #0

FECWalsh #12

FECWalsh #23

FECWalsh #27

FECWalsh #44

Pilot

Paging

Vocoder

Vocoder

Vocoder

Vocoder

more moremore

Trans-mitter,

Sector X

I Q

Short PN CodePN Offset 246

Coding Process in the Forward Direction

A Forward Channel is identified by:

its CDMA RF carrier Frequency

the unique Short Code PN Offset of the sector

the unique Walsh Code of the user

CDMAFrequency


Digital Stream 0 (DS0)

tt

0

1

2

3

4

56

87

91011

12

13

14

15

16

4

16

1

3

15

8

34

8

t

0

1

2

3

4

56

87

91011

12

13

14

15

16

81531316448

t

81531316448

64 kbs

Analog Voice Signal Sampling Quantizing

Signal Regeneration


Variable Rate Vocoding & Multiplexing(Traffic Channels Only)

Vocoders compress speech, reduce bit rate

CDMA uses a superior Variable Rate Vocoder full rate during speech low rates in speech pauses increased capacity more natural sound

Voice, signaling, and user secondary data may be mixed in CDMA frames

DSP QCELP VOCODER

Codebook

PitchFilter

FormantFilter

Coded Result Feed-back

20ms Sample

Rate Set 2 Frame SizesbitsFull Rate Frame

1/2 Rate Frame1/4 Rt.1/836

72144288

Frame Contents: can be a mixture ofVoice Signaling Secondary


Converting Bits into Symbols

The bits in a 20 ms traffic frame may include one or more of the following voice information (from the vocoder) signaling information secondary traffic information

When Forward Error Correction algorithms are applied to these information bits, the resulting 0s and 1s are called symbols bits and symbols are related in a complex

many-to-many fashionthe information in one bit is distributed among many symbols, and one symbol carries some of the information of many bits

all forward traffic frames contain 384 symbols all reverse traffic frames contain 576 symbols

Bits

Symbols

Forward ErrorCorrection


Spreading Symbols into Chips

Symbols are converted into special 64-chip patterns for transmission

there are 64 such patterns called “Walsh codes” in the forward link, just one of these patterns is

assigned to each user’s stream of symbols (code channel)

each ‘0’ symbol is replaced by the selected pattern (Walsh code)

each ‘1’ symbol is replaced by the logical negation of the selected pattern

in the reverse link, all the 64 patterns (but not their logical negations) are used in every code channel

each group of six symbols is interpreted as a binary value in the 0-63 range and replaced by the corresponding Walsh code

Symbols

Chips

Coding andSpreading


Reverting the Process

To revert the process, first the symbols are recovered as follows

In the forward direction, the mobile station correlates the received signal with the selected Walsh code pattern (integrating the power over 64 chips)

In the reverse direction, the BTS matches the received signal with each possible Walsh code and selects the pattern that produces the highest degree of correlation

When all the symbols for a 20 millisecond frame have been recovered, the Viterbi decoder is used to guess the block of bits (frame) that most probably corresponds to this block of symbols

Then the CRC of this frame is calculated to determine if the guess was successful; if not, the frame is discarded

Symbols

Chips

Despreading(integraton)

Bits

ViterbiDecoder


Forward Traffic Channels: Vocoding

Vocoding reduces the bit rate needed to represent speech Output is 20 ms frames at fixed rates:

Full Rate, 1/2 Rate , 1/4 Rate , 1/8 Rate, & Blank CRC is added to all the frames for the 13 kb vocoder, but

only to the Full and 1/2 rate frames for the 8 kb vocoder CRC is not added to the lower rate frames in the 8 kb

vocoder but that is ok because they consist mostly of background noise and have a higher processing gain

Current vocoder rates are 13 kb, 8 kb, and 8 k EVRC (Enhanced Variable Rate Coder)

To theConvolutional

Encoder

20 ms slices(1280 bits)

Variable RateVoice Coding

Add CRC Add 8 bitEncoder Tail

64 kbpsFrom MTX

ConvolutionalEncoding

Code SymbolRepetition

BlockInterleaving

Data Scrambling

Power ControlSubchannelOrthogonalSpreadingQuadratureSpreadingBasebandFiltering

VocoderProcessing

Baseband Traffic to RF Section

PCM Voice

BSC

BTS

(SymbolPuncturing)


Variable Rate Vocoder

A-to-DCONVERTER

64 kbps

VOCODER

“Codebook” Instruction(< 64 kbps)

Speech coding algorithms (digital compression) are necessary to increase cellular system capacity

Coding must also ensure reasonable fidelity, that is, a minimum level of quality as perceived by the user

Coding can be performed in a variety of ways (for example, waveform, time or frequency domain)

Vocoders transmit parameters which control “reproduction” of voice instead of the explicit, point-by-point waveform description


Wireless Data Service

The SBS selector Card Service Options include : Asynchronous Data (9600 bps) at Rate Set 1 and (14400 bps) at Rate Set 2 Group 3 Facsimile (9600 bps) at Rate Set 1 and (14400 bps) at Rate Set 2

Traffic Processing

Data ServiceOption

IWF

BTS

SBS SelectorSBS Selector

IS-95 RLPTraffic Frames

IWFTraffic

DSP


Forward Traffic Channel Generation

GainControl

BasebandFilter

BasebandFilter

I PN

Q PN

1.2288Mcps

WalshFunction

BlockInterleaving

R = 1/2, K = 9Convolutional

Encoding &Repetition

19.2Ksps

19.2 Ksps

DecimatorLong PN CodeGenerator

Scrambling

User AddressMask

(ESN-Based)

1.2288Mcps

19.2Ksps

9600 bps4800 bps2400 bps1200 bps

or14400 bps7200 bps3600 bps1800 bps

(traffic frames)

PowerControl

Bit

Decimator

800 Hz

MUX

SymbolPuncturing(13 Kb only)

28.8Ksps

bits symbols chips

CHANNEL ELEMENT


Forward Traffic Channel Frame Structure

TransmissionRate Total Reserved 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


Convolutional Encoding andSymbol Repetition

Convolutional encoding Is a means of error detection/correction Results in 2 code symbols (or more, depending on the

“R” constant) output for each bit input Symbol repetition maintains a constant 19.2 Ksps output to

be fed into the block interleaver Also allows for reduction in transmit power Reduces overall noise and increases capacity



BlockInterleaving

Data Scrambling


VocoderProcessing


PCM Voice

(SymbolPuncturing)

Variable RateOutput fromthe Vocoder

ConvolutionalEncoder

R=1/2 K=9

SymbolRepetition

19.2 kspsto Block

Interleaver

14.4 kbps 7.2 kbps 3.6 kbps 1.8 kbps

28.8 ksps14.4 ksps 7.2 ksps 3.6 ksps

9.6 kbps4.8 kbps2.4 kbps1.2 Kbps

19.2 ksps9.6 ksps4.8 ksps2.4 ksps

28.8 kspsto Symbol Puncturing

8 kb

13 kb

bits codesymbols

modulationsymbols


A Very Simple Convolutional Encoder

+

+



+

+

1011000



+

+

10110 0 0

0

1



+

+

1011 0 0

0

11

01



+

+

101 1 0

00

011

111



+

+

10 1 1

000

1101

1110



+

+

1 0 1

1000

11010

11100


Rate 1/2, k=9 Convolutional Encoding

Symbols generated as the information bits transit through the encoder, are related to all the bits currently in the register

Each information bit contributes to multiple generated symbols This pattern of inter-relationships helps detect and correct errors The length of shift register plus 1 is called the “constraint length” of the

convolutional encoder (K=9 in this case) The longer the register, the better this scheme can correct bursty errors Reduces power required to achieve same accuracy as without coding

Here, two symbols are generated for every bit input (Rate 1/2)

Code SymbolOutput

1 2 3 4 5 6 7 8

g0

g1

c0

c1

DataBit

Input

(Data Bit is discarded)

Code SymbolOutput


Symbol Repetition and Power Reduction

Symbol repetition provides a constant rate to the block interleaver Lower rates symbols are sent at reduced power levels The energy per bit across all rates is identical when integrated Overall signal power requirement (thus noise) is reduced

Data Rate(bps)

Energy perModulation Symbol

14000 / 9600

72000 / 4800

3600 / 2400

1800 / 1200

E =E /2s b

E =E /4s b

E =E /8s b

E =E /16s b

Full Energy

1/2 Energy

1/4 Energy

1/8 Energy

MATHHAMMER


Symbol PuncturingRate Set 2 (13 kbps Vocoder)

Symbol repetition maintains a constant 28.8 ksps output to puncturing section

Symbol puncturing deletes 2 of every 6 inputs based on a six-bit pattern

Unrepeated symbols for 28.8 ksps frames are also deletedConvolutional decoder in mobile station will correct these

purposeful errors Puncturing provides a constant 19.2 Ksps input to interleaver

just like in rate set 1This allows all other functions to remain exactly the same

PCM Voice



BlockInterleaving

Data Scrambling


VocoderProcessing


(SymbolPuncturing)

FromR=1/2 K=9

Convolutional Encoder

SymbolPuncturing

to the BlockInterleaver

SymbolRepetition

28.8 ksps28.8 ksps14.4 ksps 7.2 ksps 3.6 ksps

19.2 Ksps


Block Interleaving

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

below Improves survival rate of symbol data Spreads the effect of bursty interference

19.2 kspsFrom Coding& SymbolRepetition

Input Array(Normal

Sequence)24 X 16

Output Array(ReorderedSequence)

24 X 16To DataScramblingFunction

PCM Voice



BlockInterleaving

Data Scrambling


VocoderProcessing


(SymbolPuncturing)


9600 bps Block Interleaver (Input Array)

The 384 modulation symbols in a frame are input into a 24 by 16 block interleaver array (read down by columns, from left to right)

The array represents a 20 ms interval worth of information

1 25 49 73 97 121 145 169 193 217 241 265 289 313 337 3612 26 50 74 98 122 146 170 194 218 242 266 290 314 338 3623 27 51 75 99 123 147 171 195 219 243 267 291 315 339 3634 28 52 76 100 124 148 172 196 220 244 268 292 316 340 3645 29 53 77 101 125 149 173 197 221 245 269 293 317 341 3656 30 54 78 102 126 150 174 198 222 246 270 294 318 342 3667 31 55 79 103 127 151 175 199 223 247 271 295 319 343 3678 32 56 80 104 128 152 176 200 224 248 272 296 320 344 3689 33 57 81 105 129 153 177 201 225 249 273 297 321 345 36910 34 58 82 106 130 154 178 202 226 250 274 298 322 346 37011 35 59 83 107 131 155 179 203 227 251 275 299 323 347 37112 36 60 84 108 132 156 180 204 228 252 276 300 324 348 37213 37 61 85 109 133 157 181 205 229 253 277 301 325 349 37314 38 62 86 110 134 158 182 206 230 254 278 302 326 350 37415 39 63 87 111 135 159 183 207 231 255 279 303 327 351 37516 40 64 88 112 136 160 184 208 232 256 280 304 328 352 37617 41 65 89 113 137 161 185 209 233 257 281 305 329 353 37718 42 66 90 114 138 162 186 210 234 258 282 306 330 354 37819 43 67 91 115 139 163 187 211 235 259 283 307 331 355 37920 44 68 92 116 140 164 188 212 236 260 284 308 332 356 38021 45 69 93 117 141 165 189 213 237 261 285 309 333 357 38122 46 70 94 118 142 166 190 214 238 262 286 310 334 358 38223 47 71 95 119 143 167 191 215 239 263 287 311 335 359 38324 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384

16 Columns

24 r

ows


9600 bps Block Interleaver (Output Array)

1 9 5 13 3 11 7 15 2 10 6 14 4 12 8 1665 73 69 77 67 75 71 79 66 74 70 78 68 76 72 80129 137 133 141 131 139 135 143 130 138 134 142 132 140 136 144193 201 197 205 195 203 199 207 194 202 198 206 196 204 200 208257 265 261 269 259 267 263 271 258 266 262 270 260 268 264 272321 329 325 333 323 331 327 335 322 330 326 334 324 332 328 33633 41 37 45 35 43 39 47 34 42 38 46 36 44 40 4897 105 101 109 99 107 103 111 98 106 102 110 100 108 104 112161 169 165 173 163 171 167 175 162 170 166 174 164 172 168 176225 233 229 237 227 235 231 239 226 234 230 238 228 236 232 240289 297 293 301 291 299 295 303 290 298 294 302 292 300 296 304353 361 357 365 355 363 359 367 354 362 358 366 356 364 360 36817 25 21 29 19 27 23 31 18 26 22 30 20 28 24 3281 89 85 93 83 91 87 95 82 90 86 94 84 92 88 96145 153 149 157 147 155 151 159 146 154 150 158 148 156 152 160209 217 213 221 211 219 215 223 210 218 214 222 212 220 216 224273 281 277 285 275 283 279 287 274 282 278 286 276 284 280 288337 345 341 349 339 347 343 351 338 346 342 350 340 348 344 35249 57 53 61 51 59 55 63 50 58 54 62 52 60 56 64113 121 117 125 115 123 119 127 114 122 118 126 116 124 120 128177 185 181 189 179 187 183 191 178 186 182 190 180 188 184 192241 249 245 253 243 251 247 255 242 250 246 254 244 252 248 256305 313 309 317 307 315 311 319 306 314 310 318 308 316 312 320369 377 373 381 371 379 375 383 370 378 374 382 372 380 376 384

This 24 by 16 array (read down by columns, from left to right) indicates the order in which the symbols are output from the block interleaver

The effect of bursty errors during transmission is minimized (the 2k contiguous symbols containing the information to restore one data bit have been separated)

Assume that a burst of noise damages all these bits


9600 bps De-Interleaving

1 25 49 73 97 121 145 169 193 217 241 265 289 313 337 3612 26 50 74 98 122 146 170 194 218 242 266 290 314 338 3623 27 51 75 99 123 147 171 195 219 243 267 291 315 339 3634 28 52 76 100 124 148 172 196 220 244 268 292 316 340 3645 29 53 77 101 125 149 173 197 221 245 269 293 317 341 3656 30 54 78 102 126 150 174 198 222 246 270 294 318 342 3667 31 55 79 103 127 151 175 199 223 247 271 295 319 343 3678 32 56 80 104 128 152 176 200 224 248 272 296 320 344 3689 33 57 81 105 129 153 177 201 225 249 273 297 321 345 36910 34 58 82 106 130 154 178 202 226 250 274 298 322 346 37011 35 59 83 107 131 155 179 203 227 251 275 299 323 347 37112 36 60 84 108 132 156 180 204 228 252 276 300 324 348 37213 37 61 85 109 133 157 181 205 229 253 277 301 325 349 37314 38 62 86 110 134 158 182 206 230 254 278 302 326 350 37415 39 63 87 111 135 159 183 207 231 255 279 303 327 351 37516 40 64 88 112 136 160 184 208 232 256 280 304 328 352 37617 41 65 89 113 137 161 185 209 233 257 281 305 329 353 37718 42 66 90 114 138 162 186 210 234 258 282 306 330 354 37819 43 67 91 115 139 163 187 211 235 259 283 307 331 355 37920 44 68 92 116 140 164 188 212 236 260 284 308 332 356 38021 45 69 93 117 141 165 189 213 237 261 285 309 333 357 38122 46 70 94 118 142 166 190 214 238 262 286 310 334 358 38223 47 71 95 119 143 167 191 215 239 263 287 311 335 359 38324 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384

16 Columns

24 r

ows

Notice how the effect of the burst of noise is spread over the transmitted block


Forward Channel Demodulation

IS -95A/J-STD-008 requires a m inim um of four processingelem ents that can be independently directed Three elem ents m ust be capable of dem odulating m ultipath

com ponents One m ust be a “searcher” that scans and estim ates signal

strength at each pilot PN sequence offset

Correlator 1

Correlator 2

Correlator 3

Search Correlator

De-Interleaver Decoder Vocoder SpeechOutput

Co

mb

ine

r

M obile Receiver


Putting it All Together: CDMA Code Channels

The three spreading codes are used in different ways to create the forward and reverse links A forward channel exists by having a specific Walsh Code assigned to the user, and a specific

PN offset for the sector A reverse channel exists because the mobile uses a specific offset of the Long PN sequence

BTS

WALSH CODE: Individual UserSHORT PN OFFSET: Sector

LONG CODE OFFSET: individual handset

FORWARD CHANNELS

REVERSE CHANNELS

LONG CODE:Data

Scrambling

WALSH CODES:used as symbols

for robustness

SHORT PN:used at 0 offset

for tracking


Pilot Channel


Pilot Channel

Used by the mobile station for initial system acquisition Transmitted constantly by the base station The same PN sequences are shared by all base stations

Each base station is differentiated by a phase offset Provides tracking of

Timing reference Phase reference

Separation by phase provides for extremely high reusewithin one CDMA channel frequency

Acquisition by mobile stations is enhanced by Short duration of Pilot PN sequence Uncoded nature of pilot signal

Facilitates mobile station-directed handoffs Used to identify handoff candidates Key factor in performing soft handoffs


Pilot Channel Generation

The Walsh function zero spreading sequence is applied to the Pilot The use of short PN sequence offsets allows for up to 512 distinct Pilots

per CDMA channel The PN offset index value (0-511 inclusive) for a given pilot PN

sequence is multiplied by 64 to determine the actual offset Example: 15 (offset index) x 64 = 960 PN chips Result: The start of the pilot PN sequence will be delayed

960 chips x 813.8 nanoseconds per chip = 781.25 µs The quadrature spreading and baseband filtering (not shown), which are

performed as with all the other forward and reverse code channels, will be discussed later

GainControl

BasebandFilter

BasebandFilter

I PN

Q PN

1.2288Mcps

WalshFunction 0

PilotChannel(All 0’s)


Walsh Code Channel Generation

W1 = 0 0 0

0 1

W2 = 0 0 0 00 1 0 10 0 1 10 1 1 0

W4 =

W2 n = Wn Wn

Wn Wn

W1 = 1 1 1

1 0

W2 = 1 1 1 11 0 1 01 1 0 01 0 0 1

W4 =


CDMA “Short” and “Long” PN Codes

CDMA uses three PN code sequences: two “short” and one “long” The two short PN codes (called “I” and “Q”) are used for quadrature

spreading to differentiate between CDMA partitions (sectors/cells) in the forward direction

The two short codes are generated by 15-bit PN code generators. The generated strings are 215 -1 bits long plus one zero inserted following the longest string of generated zeroes (32,768); and their cycle period is 26.666... milliseconds (or 75 times every 2 seconds).

The long PN code is used for spreading and data scrambling/randomization, and to differentiate among mobile stations in the reverse direction.

The long code is generated by a 42-bit PN code generator. The generated string is 242 -1 with no zero inserted (about 4.4 trillion) bits long; and its cycle period is approximately 41 days, 10 hours, 12 minutes and 19.4 seconds.

The three CDMA PN codes are synchronized to the beginning of system time (January 6, 1980 at 00:00:00 hours)


Pilot Channel Acquisition

The mobile station starts generating the I and Q PN short sequences by itself and correlating them with the received composite signal at every possible offset In less that 15 seconds (typically 2 to 4 seconds) all possibilities (32,768)

are checked The mobile station remembers the offsets for which it gets the best

correlation (where the Ec/I0 is the best) The mobile station locks on the best pilot (at the offset that results in

the best Ec/I0), and identifies the pattern defining the start of the short sequences (a ‘1’ that follows fifteen consecutive ‘0’s)

Now the mobile station is ready to start de-correlating with Walsh code 32 to extract the Sync Channel (next section)

00...01 00...01 00...01 00...01 00...01 00...0100...01

PILOT CHANNEL(Walsh Code 0)


Sync Channel


Sync Channel Used to provide essential system

parameters Used during system acquisition stage The bit rate is 1200 bps The Sync channel has a frame

duration of 26 2/3 ms this frame duration matches the

period of repetition of the PN Short Sequences

this simplifies the acquisition of the Sync Channel once the Pilot Channel has been acquired

The Mobile Station re-synchronizes at the end of every call

The Pilot channel carries no data, therefore it has no frames.The Sync channel uses 26 2/3 ms frames.All other forward and reverse code channels use 20 ms frames.

(Acquired Pilot)

Sync Channel


Frames and Messages

Logical unit of transmission Fixed length

no need for length info Each frame includes one or more

overhead bits in addition to the “payload” of information bits

these overhead bits define the structure of the frame

Logical unit of information Variable length

must include length info A message is broken into small

pieces that can fit in the payload portion of successive frames

one frame overhead bit could be used to identify the initial segment of a message

FRAME MESSAGE

+ + + +

+ +1 0 0 0

FRAME

Sync

Traffic

MESSAGE

FRAME


Sync Channel Generation

There are 32 bits (1200 bps x 0.02666... second) in one Sync Channel frame The Rate 1/2 convolutional encoder doubles the bit rate, and the resulting 0s and 1s

are now called “code symbols” there are 64 code symbols in a Sync Channel frame

The repetition process doubles the rate again, and each repetition of a code symbol is now called a “modulation symbol” there are 128 modulation symbols in a Sync Channel frame

Four copies of Walsh code #32 are used to spread each modulation symbol, resulting in a x256 rate increase; the resulting 0s and 1s are now called “chips” there are 32,768 chips in a Sync Channel frame (1024 chips per original bit)

GainControl

BasebandFilter

BasebandFilter

I PN

Q PN

1.2288Mcps

WalshFunction 32

1200 bps

BlockInterleaving

R = 1/2, K = 9Convolutional

Encoding &Repetition

4800 bps

4800 bps

bitsmodulation

symbols chips


Sync Channel Block Interleaver(Input Matrix)

1 9 17 25 33 41 49 57

1 9 17 25 33 41 49 57

2 10 18 26 34 42 50 58

2 10 18 26 34 42 50 58

3 11 19 27 35 43 51 59

3 11 19 27 35 43 51 59

4 12 20 28 36 44 52 60

4 12 20 28 36 44 52 60

5 13 21 29 37 45 53 61

5 13 21 29 37 45 53 61

6 14 22 30 38 46 54 62

6 14 22 30 38 46 54 62

7 15 23 31 39 47 55 63

7 15 23 31 39 47 55 63

8 16 24 32 40 48 56 64

8 16 24 32 40 48 56 64


Sync Channel Block Interleaver(Output Matrix)

1 3 2 4 1 3 2 4

33 35 34 36 33 35 34 36

17 19 18 20 17 19 18 20

49 51 50 52 49 51 50 52

9 11 10 12 9 11 10 12

41 43 42 44 41 43 42 44

25 27 26 28 25 27 26 28

57 59 58 60 57 59 58 60

5 7 6 8 5 7 6 8

37 39 38 40 37 39 38 40

21 23 22 24 21 23 22 24

53 55 54 56 53 55 54 56

13 15 14 16 13 15 14 16

45 47 46 48 45 47 46 48

29 31 30 32 29 31 30 32

61 63 62 64 61 63 62 64

Let’s assume that a burst of noise affects these symbols


Sync Channel Block Interleaver(Original Order Restored)

1 9 17 25 33 41 49 57

1 9 17 25 33 41 49 57

2 10 18 26 34 42 50 58

2 10 18 26 34 42 50 58

3 11 19 27 35 43 51 59

3 11 19 27 35 43 51 59

4 12 20 28 36 44 52 60

4 12 20 28 36 44 52 60

5 13 21 29 37 45 53 61

5 13 21 29 37 45 53 61

6 14 22 30 38 46 54 62

6 14 22 30 38 46 54 62

7 15 23 31 39 47 55 63

7 15 23 31 39 47 55 63

8 16 24 32 40 48 56 64

8 16 24 32 40 48 56 64


Sync Channel Structure

1200 bps80 ms, 96 bits

Ns = Number of SyncChannel Superframes needed for message transmission

1 0 0 0 0 0

Sync Channel Superframe Sync Channel Superframe

Sync Channel Message

Message BodyMSG_LENGTH CRC

26.67 ms32 bits

31 bits

8 bits 30 bits2-1146 bits

as required

Sync Channel Frame Body

Sync Channel Frame

SOM

Padding

Sync Channel Message Capsule (93 x Ns bits)

Sync Channel Message (8 x MSG_LENGTH)


Sync Channel Message Body Format

MSG_TYPE (‘00000001’)

P_REV

MIN_PREV

SID

NID

PILOT_PN

LC_STATE

SYS_TIME

LP_SEC

LTM_OFF

DAYLT

PRAT

CDMA_FREQ

8

8

8

15

16

9

42

36

8

6

1

2

11

Field Length(bits)

Total : 170


Sync Message ParametersSync Message Parameters

• Message Type (MSG_TYPE) – Identifies this message and determines its structure (set to the fixed value of ‘00000001’)

• Protocol Revision Level (P_REV) – Shall be set to ‘00000001’

• Minimum Protocol Revision Level (MIN_P_REV) – 8-bit unsigned integer identifying the minimum protocol revision level required to operate on this system. Only personal stations that support revision numbers greater than or equal to this field can access the system

• System ID (SID) – 16-bit unsigned integer identifying the system

• Network ID (NID) – 16-bit unsigned integer identifying the network within the system (defined by the owner of the SID)

• Pilot PN Sequence Offset Index (PILOT_PN) – Set to the pilot PN offset for the base station (in units of 64 chips), assigned by the network planner

• Long Code State (LC_STATE) – Provides the mobile station with the base station long code state at the time given by the SYS_TIME field, generated dynamically

• System Time (SYS_TIME) – GPS system-wide time as 320 ms after the end of the last superframe containing any part of this message, minus the pilot PN offset, in units of 80 ms, generated dynamically


Sync Channel Message Parameters (cont)Sync Channel Message Parameters (cont)

• Leap Seconds (LP_SEC) – Number of leap seconds that have occurred since the start of system time (January 6, 1980 at 00:00:00 hours) as given in the SYS_TIME field, generated dynamically

• Local Time Offset (LTM_OFF) – Two’s complement offset of local time from system time in units of 30 minutes, generated dynamically

• Current local = SYS_TIME – LP_SEC + LTM_OFF

• Daylight savings time indicator (DAYLT) – Determined by the network planner

• 1 if daylight savings in effect in this base station• 0 otherwise

• Paging Channel Data Rate (PRAT) – The data rate of the paging channel for this system, determined by the network planner

• 00 if 9600 bps• 01 if 4800 bps

• CDMA Frequency Assignment (CDMA_FREQ) – The CDMA channel number, in the specified CDMA band class, corresponding to the frequency assignment for the CDMA Channel containing a Primary Paging Channel, determined by the network planner


Paging Channels


Paging Channels

Up to seven paging channels can be supported on a single CDMA frequency assignment

Channel 1 (Walsh function 1) is the Primary Paging Channel Additional Paging Channels use Walsh functions 2 through 7 Unused paging channels can be used as Forward Traffic Channels Two rates are supported: 9600 and 4800 bps (PRAT parameter in the

Sync Channel Message) A single 9600 bps Paging Channel can support about 180 pages per

second

Used by the base station to transmit system overhead informationand mobile station-specific messages.


Paging Channel Generation

There are 192 [96] bits (9600 [4800] bps x 0.020 second) in one Paging Channel frame

The Rate 1/2 convolutional encoder doubles the bit rate, resulting” 384 [192] code symbols in a Paging Channel frame

If the 4800 bps rate is used, the repetition process doubles the rate again, so that, at either rate, 384 modulation symbols per Paging Channel frame result

384 modulation symbols per frame times 50 frames per second = 19.2 Ksps One copy of Walsh code #1 (or #2, ... or #7) is used to spread each modulation

symbol. This results in a x64 rate increase to 1.2288 Mcps that is, 24,576 chips per Paging Channel frame, or 128 [256] chips per original

bit at 9600 [4800] bps

GainControl

BasebandFilter

BasebandFilter

I PN

Q PN

1.2288Mcps

WalshFunction 1-7

9600 bps4800 bps

BlockInterleaving

R = 1/2, K = 9ConvolutionalEncoding &Repetition

19.2Ksps

19.2Ksps

DecimatorLong PN CodeGenerator

Scrambling

Paging Channel

Address Mask

1.2288Msps

19.2Ksps


Paging Channel Structure

R = 9600 or 4800 bps

(1) First new capsule in slot, Synchronized Capsule(2) Unsynchronized Capsules(3) Synchronized Capsules

8 x MSG_LENGTH as required

SCI

8 bits 30 bits(see notein text)

163.84 s, 163.84 x R bits

2048 slots

8 Half Frames per Slot

(1) (2) (3)

10 ms

SCI : Synchronized Capsule Indicator

Maximum Paging Channel Slot Cycle

Slot Channel 0 Slot Channel “n” Slot Channel 2047

Half Frame Half Frame Half Frame Half Frame Half Frame

Half Frame Body Half Frame Body Half Frame Body Half Frame Body Half Frame Body0 1 0 0 10

age Capsule Message Capsule Message Capsule Message

PaddingMessage Paging Channel Message Paging Channel Message Padding Paging Ch

MSG_LENGTH Message Body CRC


Lesson Review

1. What reference channel is used for acquisition, timing, and as a phase reference for coherent demodulation?

Pilot channel2. Lower data rates are transmitted at reduced power rates.

True3. The frame duration of what channel matches the period of repetition for of the

short PN sequences?

Sync channel4. The sync channel is identified by what Walsh code function?

325. The pilot channel is identified by what Walsh code function?

06. Convolutional encoding occurs before block interleaving (on the forward

channel).

True


Lesson Review

7. What is the purpose of the paging channel?

To transmit system overhead information and mobile station specific messages.8. What Walsh functions are reserved for the paging channels?

1 through 79. Unused paging channels can be used as what type of channel?

Traffic channels10. The effect of bursty errors are minimized by what function?

Block interleaving and de-interleaving


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CDMA Technology Overview

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