CDMA Technology Overview

CDMA Technology Overview February, 2001 - Page 1-1

CDMA Technology CDMA Technology OverviewOverview

Lesson 2 – Spectrum Usage and System Capacity


Spectrum Usage and System Capacity:Signal Bandwidth, Vulnerability and Frequency Reuse

Each wireless technology (AMPS, NAMPS, D-AMPS, GSM, CDMA) uses a specific modulation type with its own unique signal characteristics

The total traffic capacity of a wireless system is determined largely by radio signal characteristics and RF design

RF signal vulnerability to Interference dictates how much interference can be tolerated, and therefore how far apart same-frequency cells must be spaced

For a specific S/N level, the Signal Bandwidth determines how many RF signals will “fit” in the operator’s licensed spectrum

AMPS, D-AMPS, N-AMPS

CDMA

30 30 10 kHz

200 kHz

1250 kHz

1 3 1 Users

8 Users

22 Users1

1

11

1

11

11

1

11

1

1

12

34

43

2

56

17

Typical Frequency Reuse N=7



Vulnerability:C/I 17 dB

Vulnerability:C/I 12-14 dB

Vulnerability:Eb/No 6 dB

GSM

17 dB = 101.7 5014 dB = 101.4 25 12 dB = 101.2 16


Relationship Between Eb/N0 and S/N

Eb =S

R

Signal Power

Bit Rate = N0 =

N

W

Noise Power

Bandwidth=

=S

R

W

N X =

S

N

W

R X

S

R

N

W

Eb

N0

=

Signal to Noise

ProcessingGain

E / t

B / t=

W

R=

1,250,000

14,400= 87 =

1.94

10 = 19.4dB

W

R=

1,250,000

9,600= 130 =

2.11

10 = 21.1dB8 Kb vocoder

(Full Rate)

13 Kb vocoder(Full Rate)


S/N Advantage of CDMA

AMPS

N-AMPS

D-AMPS

GSM

CDMA

Analog FM

Analog FM

DQPSK

GMSK

QPSK/OQPSK

30 KHz.

10 KHz.

30 KHz.

200 KHz.

1,250 KHz.

C/I 17 dB

C/I 17 dB

C/I 17 dBC/I 12-14

dBEb/No 6dB

Tech-nology Modulation Type Channel

BandwidthQuality

Indicator

S/N 17 dB

S/N 17 dB

S/N 17 dB

S/N 12 to 14 dB

S/N –13.4 dB

S/N

17 dB = 101.7 5014 dB = 101.4 25 12 dB = 101.2 16

-13.4 dB = 10-1.34 0.046 =

S

N 10 0.6

10 1.94= = 10 -1.34 = -13.4 dB

Signal to NoiseProcessing Gain (W/R)

S

NX = 10 0.610 1.94

Eb N0

122


Overlaying CDMA on an AMPS System

Each CDMA Channel: 1.250 MHz ÷ 30 kHz = 41.7 = ~41 AMPS channelsEach Guard Band: 260 kHz ÷ 30 kHz = 8.7 = ~9 AMPS channels

260 KHz 260 KHz1.25 MHz Nominal Bandwidth

Frequency

Po

we

r1.77 MHz

CDMA CARRIER

41 AMPS channels 41 AMPS channels

9 AMPSchannels

41 AMPS channels

41 AMPS channels

CDMA CDMA CDMA CDMA CDMA

AVAILABLE AVAILABLE

885 KHzMinimum Separation between AMPS/TDMA and CDMA center frequency:

(1,250 kHz ÷ 2) + 260 kHz = 885 kHz

TOTAL: 1.77 MHz ÷ 30 kHz = 59 AMPS channels

GUARDBAND

GUARDBAND


CDMA 800 MHz Cellular Spectrum Usage

All CDMA RF carriers are 1.25 MHz. wide can serve ~22 users w/8 kb vocoder (~17 users w/13 kb vocoder)

The cellular spectrum of one operator is 12.5 MHz. wide. You’d expect that 10 CDMA carriers would fit. However, only 9 carriers can be used operators must maintain a “token” AMPS presence for several years “guard bands” are required at the edges of frequency blocks or any

frequency boundaries between CDMA/non-CDMA signals no guard bands are required between adjacent CDMA carriers

Possible CDMA Center Freq. Assignments

Channel Numbers

Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)824MHz

849MHz

869MHz

894MHz

otherusesA” A”A B A’ B’

1 10 10 1.5 2.5

A B A’ B’

1 10 10 1.5 2.5

991

10231 333

334

666667

716717

799

991

10231 333

334

666667

716717

799

~300 kHz. “guard bands” possibly required if adjacent-frequency signals are non-CDMA (AMPS, TDMA, ESMR, etc.)


Deploying CDMA on the 1900 MHz Band

CDMA

1770 ÷ 50 = 35.4

1250 ÷ 50 = 25

260 ÷ 50 = 5.2

260 kHz 260 kHz1.25 MHz Nominal Bandwidth

Frequency

Po

we

r

1.77 MHz

CDMA CARRIER

• All frequenciesare available fornon-CDMA use

• Only thefrequencies in thegray area areavailable for nonCDMA use

• All frequenciesare available fornon-CDMA use

• Only thefrequencies in thegray area areavailable for nonCDMA use


CDMA PCS 1900 MHz Spectrum Usage

A, B, and C licenses can accommodate 11 CDMA RF channels in their 30 MHz of spectrum

D, E, and F licenses can accommodate 3 CDMA RF channels in their 10 MHz of spectrum

260 kHz guard bands are required on the edges of the PCS spectrum to ensure no interference occurs with other applications just outside the spectrum

Guard Bands

Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)1850 MHz

BTA

BTA

BTA

BTA

BTA

BTA

Paired Bands

MTA BTAMTABTA MTAMTA

1910 MHz

1930MHz

1990MHz

Data Voice

A D B E F C A D B E F C

15 51010 1515151515 555 55

Licensed Licensed

Unlicensed

0

Channel Numbers 299

300

400

699

700

800

900

1199 0

299300

400

699700

800

900

1199


Overlaying CDMA on the 1900 MHz Band

Each CDMA Channel: 1.250 MHz ÷ 50 kHz = 25 channels

Each Guard Band: 260 kHz ÷ 50 kHz = 5.2 = ~5 channels

TOTAL: 1.77 MHz ÷ 50 kHz = 35.4 = ~ 35 channels

260 KHz 260 KHz1.25 MHz Nominal Bandwidth

Frequency

Po

we

r

1.77 MHz

CDMA CARRIER

Just as with the CDMA on AMPS overlay, a GUARD ZONE is also needed

GUARDBAND

GUARDBAND


Number of Voice Channels (As AMPS Channels Are Converted to Digital)

0

50

100

150

200

1 2 3 4 5 6 7 8 9 10S1

S4

AMPS

TDMA

13 kbpsCDMA

8 kbpsCDMA

Num

ber

of V

oice

Cha

nnel

s

Number of CDMA Carriers0 1 2 3 4 5 6 7 8 9

200

150

100

50

0


CDMA Frequency Channel Assignment at 800 MHz Cellular

IS-95 RECOMMENDS TO START CDMA DEPLOYMENTWITH EITHER THE PRIMARY OR THE SECONDARY CHANNEL

1

334

667

991

1023

333

666

715

799

716

ChannelNumbers

A Band B Band A’A” B’

1013 31 73 115 157 199 241 283 384 426 468 510 552 594 636 691 777

CDMA A-Band Carriers CDMA B-Band Carriers

8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 9 9 8

* **** Requires frequency coordination with

non-cellular interferers

** Requires frequency coordination with A-band carrier

A Band Primary Channel 283A Band Secondary Channel 691

B Band Primary Channel 384B Band Secondary Channel 777


CDMA Frequency Clearing: A-band(N=7 Reuse Pattern)

To deploy a CDMA carrier centered on AMPS/TDMA Channel 283, AMPS/TDMA Channels 254 through 312, inclusive, must be cleared from the CDMA coverage area

The CDMA channel is implemented, centered on AMPS/TDMA Channel 283. The first usable AMPS/TDMA Channels (outside of the Guard Zone) are Channels 253 and 313

333 332 331 330 329 328 327 326 325 324 323 322 321 320 319 318 317 316 315 314 313

312 311 310 309 308 307 306 305 304 303 302 301 300 299 298 297 296 295 294 293 292

291 290 289 288 287 286 285 284 283 282 281 280 279 278 277 276 275 274 273 272 271

270 269 268 267 266 265 264 263 262 261 260 259 258 257 256 255 254 253 252 251 250

249 248 247 246 245 244 243 242 241 240 239 238 237 236 235 234 233 232 231 230 229

228 227 226 225 224 223 222 221 220 219 218 217 216 215 214 213 212 211 210 209 208

207 206 205 204 203 202 201 200 199 198 197 196 195 194 193 192 191 190 189 188 187

186 185 184 183 182 181 180 179 178 177 176 175 174 173 172 171 170 169 168 167 166

165 164 163 162 161 160 159 158 157 156 155 154 153 152 151 150 149 148 147 146 145

144 143 142 141 140 139 138 137 136 135 134 133 132 131 130 129 128 127 126 125 124

123 122 121 120 119 118 117 116 115 114 113 112 111 110 109 108 107 106 105 104 103

102 101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82

81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61

60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40

39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19

18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

1A 2A 3A 4A 5A 6A 7A 1B 2B 3B 4B 5B 6B 7B 1C 2C 3C 4C 5C 6C 7C

N = 7


1A 2A 3A 4A 5A 6A 7A 1B 2B 3B 4B 5B 6B 7B 1C 2C 3C 4C 5C 6C 7C

334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354

355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375

376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396

397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417

418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438

439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459

460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480

481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501

502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522

523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543

544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564

565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585

586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606

607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627

628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648

649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666

N = 7

CDMA Frequency Clearing: B-band(N=7 Reuse Pattern)

To deploy a CDMA carrier centered on AMPS/TDMA Channel 384, AMPS/TDMA Channels 355 through 413, inclusive, must be cleared from the CDMA coverage area

The CDMA channel is implemented, centered on AMPS/TDMA Channel 384. The first usable AMPS/TDMA Channels (outside of the Guard Zone) are Channels 354 and 414


Overlay Guard Zone Deployment

AMPS Only Cellsapprox 19 channels per sector

CDMA & AMPS Cellsapprox 16 channels per sector

one CDMA channel/carrier/frequency

( 42 + 9 + 9 ) ÷ 21 = 2.8 = ~3 AMPS channels must be cleared per sector in the CDMA & AMPS area and in the Guard Zone to make

room for the first CDMA channel/carrier/frequency

The Guard Zones are needed between CDMA and other systems because CDMA increases the noise floor for those systems

AMPS Only Cells (GUARD ZONE)approx 16 channels per cell


Other Technologies: Avoiding Interference

In conventional radio technologies, the desired signal must be strong enough to override any interference

AMPS, TDMA and GSM depend on physical distance separation to keep interference at low levels

Co-channel users are kept at a safe distance by careful frequency planning

Nearby users and cells must use different frequencies to avoid interference

2

3

4

5 6

7

4

6

4

7 2

7

2

5

3

5

36

1

1

1

1

1

1

1

AMPS-TDMA-GSM

Figure of Merit: C/I(carrier/interference ratio)

AMPS: +17 dBTDMA: +14 to 17 dBGSM: +12 to 14 dB


Other Technologies: Avoiding Interference

In conventional radio technologies, the desired signal must be strong enough to override any interference

AMPS, TDMA and GSM depend on physical distance separation to keep interference at low levels

Co-channel users are kept at a safe distance by careful frequency planning

Nearby users and cells must use different frequencies to avoid interference

2

3

4

5 6

7

4

6

4

7 2

7

2

5

3

5

36

1

1

1

1

1

1

1

AMPS-TDMA-GSM

Figure of Merit: C/I(carrier/interference ratio)

AMPS: +17 dBTDMA: +14 to 17 dBGSM: +12 to 14 dB


CDMA: Using a New Dimension

All CDMA users occupy the same frequency at the same time! Frequency and time are not used as discriminators

CDMA operates by using CODES to discriminate between users

CDMA interference comes mainly from nearby users

Each user is a small voice in a roaring crowd -- but with a uniquely recoverable code

Transmit power on all users must be tightly controlled so their signals reach the base station at the same signal level

Figure of Merit: Ec/Io, Eb/No

(energy per chip [bit] /interference [noise] spectral density)

CDMA: Ec/Io -17 to -2 dBCDMA: Eb/No ~+6 dB


ConvolutionalEncoder

R=1/2 K=9

Symbol Repetition

PacketRouting

9600 bps4800 bps2400 bps1200 bps

T-164 kbsPCM

BlockInterleaver

19200 sps9600 sps4800 sps2400 sps

19.2 Ksps

Long CodePN

Generator

1.2288 Mcps

Decimator64

Decimator64

MUX

DataScrambling

WalshCode

Wt

User AddressMask (ESN)

19.2 Ksps

I PN+t

Q PN +t

Up-Conversion

I other users

Qother users

Correlator

Correlator

Correlator

Correlator

Combiner

BlockDe-Interleaver

ViterbiDecoder

VoiceCoding

SwitchingPacketRouting

Switching

T-164 kbsPCM

BCN

BCNT-1

Unch.

T-1Unch.

PN +t

CDSUCDSU

PacketRouting

VoiceCoding

CDSUPacketRouting

CDSU

BCN

BCN BCN

800 Hz

HPA

LNA

IF RF RF

19.2 Ksps

1.2288 Mcps

BTU/STU

RFIF

De-modulation

1.2288 Mcps

IFModulation

DownConversion

MTX BSC BTS

Power ControlDecision

The Network View


The Handset View

Duplexer &Bandpass

FiltersIF

BPFMixerLNA

LocalOscillator

(Synthesized)

Traffic Correlator

PN Generator Walsh Generator

Traffic Correlator


Traffic Correlator


Vocoder

Search Correlator (Pilots)

PN Generator Walsh =0 CPU &Control

Algorithms

VocoderConv. Encoder& Symbol Rep.

BlockInterleaver

OrthogonalModulator

Data BurstRandomizer

Direct Seq.Spreading

QuadratureSpreading

BasebandFiltering

IF Modulator

PowerAmplifier

IF

AntennaReceiver

Transmitter

voice bits

voice bits

audio

audio

symbols

chips

Mixer

chips symbols symbols

RF IF

RF

RF

LO

LO

IF

Open Loop Pwr Control

messagebits

message bitsLONG CODE Generator

IF

IF Transmit Gain Adjust: Closed Loop Pwr Control

IF ViterbiDecoder


Lesson Review

1. What is the C/I ratio (in decibels) for GSM users?

12 – 14 dB

2. Processing Gain (W/R) is

the rate of bit rate to bandwidth

the rate of bandwidth to bit rate

all of the above

none of the above

The rate of bandwidth to bit rate

3. Frame Error Rate (FER) is a better performance measurement that Bit Error Rate (BER)?

True


Lesson Review, continued

4. All CDMA RF carriers

are 1.25 MHz wide

can serve ~ 22 users with a 8kb vocoder

can serve ~ 17 users with a 13kb vocoder

all of the above

none of the above

all of the above

5. As the number of voice channels increase, the number of AMPS carriers decrease.

True

6. Long Code PN generation occurs in the

MTX

BSC

BTS

none of the above

BTS


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