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CDMA Key Technology

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CDMA Key Technology. ZTE Corporation CDMA Division. CDMA Key Technology. Spread Spectrum Communication Code Division Multiple Access Power Control Diversity Soft Handoff Rake Receiver Variable Rate Vocoder. Power Control. Why power control is needed for CDMA. Near-far problem - PowerPoint PPT Presentation
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CDMA Key Technology ZTE Corporation CDMA Division
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Page 1: CDMA Key Technology

CDMA Key Technology

ZTE Corporation

CDMA Division

Page 2: CDMA Key Technology

CDMA Key Technology

Spread Spectrum Communication

Code Division Multiple Access

Power Control

Diversity

Soft Handoff

Rake Receiver

Variable Rate Vocoder

Page 3: CDMA Key Technology

Power Control

Why power control is needed for CDMA Near-far problem If all mobiles transmitted at the same power level, the base

station would receive unnecessarily strong signals from mobiles nearby and extremely weak signals from mobiles that are far away. This will reduce the capacity of the system.

Power Control Power control is a CDMA feature that enables mobiles to

adjust the power at which they transmit. This ensures that the

base station receives all signals at the appropriate power.

Both forward and reverse links uses power control techniques.

Page 4: CDMA Key Technology

Power Control (1)

The Need for Power Control CDMA is an Interference-limited system (not frequency-limited) Same frequency transmission: system internal interference critical to

system capacity and voice quality Transmit power of each mobile should be controlled to limit interference Changes of RF environment: fast and slow fading, shadowing, external

interference. Near and Far effect: mobile closer to the base station transmit less power

than those far away

Objective: Reducing interference by limiting transmitted power on the forward and reverse links while maintaining link quality

Meet user-defined performance objectives: BER, FER, capacity, dropped-call rate, coverage

Page 5: CDMA Key Technology

Power Control (2) Reverse Link Power Control: on the basis of E/I ratio

Open Loop Power Control : No involvement of BS, MS determines initial power transmitted o

n the access and traffic channels, adjustment for path loss Closed loop control :inner loop control/outer loop control: MS seizes a forward traffic channel and receives control bits, MS

and BS engage in closed-loop power control Inner loop control: Keeps the mobile as close to its target E/I

ratio as possible Outer loop control: Adjust the base station target E/I ratio for

a given mobile

Forward Link Power Control : on the basis of FER Reducing both in-cell interference and other cell/sector interferenc

e FERs are measured instead of E/I

Page 6: CDMA Key Technology

Power Control (3)

TargetPower control

algorithm

Adjustment instruction

MS

Transmitting Power

ob I/E

ob I/EInformation packet

Error rate algorithmAdjustment of Target E/I

Inner loop

Outer loop

BS

ob I/E

(Constant) Transmitting Power, Control range:±32 dB

Receiving Power

MS

Reverse Open Loop Power Control

Reverse Closed Loop Power Control

Page 7: CDMA Key Technology

Power Control (4)

Base Station MSFER

Transmitting Power

Forward Link Power Control

Page 8: CDMA Key Technology

Power Control (Continued)

Reverse Open Loop

Mobile BTS

Reverse Open LoopPower Control

Reverse Link Open Loop Power Control An initial estimation of required transmission power by the mobile Coarse measure of path loss based upon total receive power at mobile Receive Power+Transmitted Power=-73(dbm)+Parameter

Page 9: CDMA Key Technology

Power Control (Continued)

Reverse Closed Loop

Reverse Link Closed Loop Power Control Used to compensate for asymmetries in forward/reverse links Up/down commands sent to mobile based upon SNR measured at Base Station

compared to a specified threshold Transmitted 800 times per second at 1dB increments

Mobile BTS

Signal StrengthMeasurement

Setpoint

or

Reverse Closed LoopPower Control

Page 10: CDMA Key Technology

Power Control (Continued)

Reverse Outer Loop

Reverse Outer Loop Power Control Setpoint is varied according to FER on reverse link (measured at the Bas

e Station Controller) Sampled at 50 frames per second rate (20msec) Setpoint adjusted every 1-2 seconds

FER

Mobile BTS BSC

Reverse Outer Loop Power

Control

Signal StrengthMeasurement

Setpoint

or

Reverse Closed LoopPower Control

Page 11: CDMA Key Technology

N

Y

N

Y

BS

MS

BS

measurement Nt Eb

Stat. Backward link

FER

Outer loop adjustment

algorithm, new 0 N Eb

Power control

(bit) 0

Transmit Power control

(bit) 1

Transmit power

adjustment Power control

command detection

=1% ?

Nt Eb >

0 N Eb ?

1%

Outer-loop adjustment

Closed-loop control

Power Control (Continued)

Page 12: CDMA Key Technology

Power Control (Continued)

Forward Link

Forward Link Power Control Base station slowly decreases power to each mobile As FER (measured at the mobile) increases, the mobile requests a raise

in forward link power

FER

Mobile BTS BSC

Adjust Fwd.power

Forward Link Power Control

Page 13: CDMA Key Technology

Power Control (Continued)CDMA Power Control Summary

All types of power control work simultaneously to minimize transmit power

FER FER

Mobile BTS BSC

Signal StrengthMeasurement

Setpoint

or

Adjust Fwd.power

Reverse Outer Loop Power

Control

Reverse Closed LoopPower Control

Forward Link Power Control

Reverse Open LoopPower Control

Page 14: CDMA Key Technology

Diversity

Three types of diversity in CDMA.

Time DiversityFrequency DiversitySpace Diversity

Page 15: CDMA Key Technology

Diversity Reception (1)

Definition: Simultaneous reception of multiple input signals. Combining and

correlation of the signals help reduce multi-path fading

Types of Diversity: compensation for fading factors of frequency, space and time Frequency diversity reception: spread spectrum

transmission Space diversity reception

Two or more separate antennas for reception and transmission to guarantee separate propagation fading/loss

Two BTS: in case of soft handoff

Reception

Reception

BS 1 BS 2

Page 16: CDMA Key Technology

Diversity Reception (2)

Time Diversity Reception RAKE receivers of both BS and MS. When the

delay of the signals is larger than 1μs, RAKE

receiver extract them without confusion

Reception window 1

Reception window 2

Page 17: CDMA Key Technology

Rake Receiver The rake receiver is a CDMA featu

re that turns what is a problem in other technologies into an advantage for CDMA.

Signals sent over the air can take multi-paths to the receiver. It can result in the receiving getting serveral versions of the same signal but at slightly different times. Multi-paths can cause a loss of signal through cancellation in other technologies.

CDMA rake receiver is multiple receivers in one. The rake receiver identifies the three strongest multi-path signals and combines them to produce one very strong signal.

Multi-path Propagation

A

t

10-15 dB

Rayleigh Fading

Page 18: CDMA Key Technology

Diversity (Continued)

Time Diversityg0

g1

C0

C1

Input

C 2g2

Output

1 33 65 97 129 161 193 225 257 289 321 353 385 417 449 481 513 5452 34 66 98 130 162 194 226 258 290 322 354 386 418 450 482 514 5463 35 67 99 131 163 195 227 259 291 323 355 387 419 451 483 515 5474 36 68 100 132 164 196 228 260 292 324 356 388 420 452 484 516 5485 37 69 101 133 165 197 229 261 293 325 357 389 421 453 485 517 5496 38 70 102 134 166 198 230 262 294 326 358 390 422 454 486 518 5507 39 71 103 135 167 199 231 263 295 327 359 391 423 455 487 519 5518 40 72 104 136 168 200 232 264 296 328 360 392 424 456 488 520 5529 41 73 105 137 169 201 233 265 297 329 361 393 425 457 489 521 553

10 42 74 106 138 170 202 234 266 298 330 362 394 426 458 490 522 55411 43 75 107 139 171 203 235 267 299 331 363 395 427 459 491 523 55512 44 76 108 140 172 204 236 268 300 332 364 396 428 460 492 524 55613 45 77 109 141 173 205 237 269 301 333 365 397 429 461 493 525 55714 46 78 110 142 174 206 238 270 302 334 366 398 430 462 494 526 55815 47 79 111 143 175 207 239 271 303 335 367 399 431 463 495 527 55916 48 80 112 144 176 208 240 272 304 336 368 400 432 464 496 528 56017 49 81 113 145 177 209 241 273 305 337 369 401 433 465 497 529 56118 50 82 114 146 178 210 242 274 306 338 370 402 434 466 498 530 56219 51 83 115 147 179 211 243 275 307 339 371 403 435 467 499 531 56320 52 84 116 148 180 212 244 276 308 340 372 404 436 468 500 532 56421 53 85 117 149 181 213 245 277 309 341 373 405 437 469 501 533 56522 54 86 118 150 182 214 246 278 310 342 374 406 438 470 502 534 56623 55 87 119 151 183 215 247 279 311 343 375 407 439 471 503 535 56724 56 88 120 152 184 216 248 280 312 344 376 408 440 472 504 536 56825 57 89 121 153 185 217 249 281 313 345 377 409 441 473 505 537 56926 58 90 122 154 186 218 250 282 314 346 378 410 442 474 506 538 57027 59 91 123 155 187 219 251 283 315 347 379 411 443 475 507 539 57128 60 92 124 156 188 220 252 284 316 348 380 412 444 476 508 540 57229 61 93 125 157 189 221 253 285 317 349 381 413 445 477 509 541 57330 62 94 126 158 190 222 254 286 318 350 382 414 446 478 510 542 57431 63 95 127 159 191 223 255 287 319 351 383 415 447 479 511 543 57532 64 96 128 160 192 224 256 288 320 352 384 416 448 480 512 544 576

Convolutional

Interleaving

Page 19: CDMA Key Technology

Diversity (Continued)

Frequency Diversity

Bandwidth of Traditional Signal : 200~300 KHz

Bandwidth of CDMA Signal : 1.25MHz

200 - 300 KHz

1.25 MHz

50 times

Page 20: CDMA Key Technology

Diversity (Continued)

Space Diversity

Correlator

Correlator

Correlator

Rake Receiver Soft Handoff

MS

RX1

RX0

Diversity Antenna

Diversity receiver is useful in reducing multipath fading

Page 21: CDMA Key Technology

Soft Handoff A soft handoff establishes a

connection with the new BTS prior to breaking the connection with the old one. This is possible because CDMA cells use the same frequency and the mobile uses a rake receiver.

The CDMA mobile assists the network in the handoff. The mobile detects a new pilot as it travels to the next coverage area. The new BTS then establishes a connection with the mobile. This new communication link is established while the mobile maintains the link with the old BTS.

Soft handoffs are also called “make-before-break”. It reduces call drop.

Soft Handoff

Softer Handoff

Soft/Softer Handoff

Page 22: CDMA Key Technology

Soft Handoff (1)

Features:

First establish target connection, then cut off the original connection

Seamless communication, less call dropping, high voice quality

Types of soft handoff: Inter sector: softer handoff, performed by BTS

Inter BS : soft handoff, performed by BSC

Inter BSC/MSC Soft Handoff CDMA system with High-speed packet switching functions

Page 23: CDMA Key Technology

Soft Handoff (2)

BTS BTS BTS

BSC

HIR S

SVBS

BSC

HIR S

SVBS

M SC M SC M SC

BSC

HIR S

SVBS

BTS1

BSC

H IR S

SVBS

M SC

BTS2 BTS1

BSC

H IR S

SVBS

M SC

BTS2 BTS1

BSC

H IR S

SVBS

M SC

BTS2

Page 24: CDMA Key Technology

BS A

BS B

BS C

Threshold

Threshold Hand off execution area

Pilot Strength Ec/No

tt1 t2 t3

Timing

r1

r2

Soft Handoff from BS A to BS B

Soft Handoff Process (3)

Page 25: CDMA Key Technology

Variable Rate Vocoder Three types of vocoder 8K QCELP

13K QCELP

8K EVRC(Enhanced variable rate codec)

Four kinds of speed for 8K QCELP

9.6 Kbps - High Speed

4.8 Kbps - Middle Speed

2.4Kbps - Low Speed

1.2Kbps - Not Talk or Noise It reduces the transmitted power, s

o its interference to all CDMA system is reduced and the capacity of all system increases.

Page 26: CDMA Key Technology

Voice Coding

64kPCM

13kGSM

8kCDMA

13kCDMA

Q-CELP Voice Coder with variable rate Voice quality of CDMA 8K Vocoder equals that of GSM 13K

Vocoder CDMA13K Vocoder has good Voice quality close to that of

wire telephone with strong background noise reduction CDMA EVRC very close to CDMA 13K Vocoder

Page 27: CDMA Key Technology

Sampling

8KHz

160Sampled

Value

Tone parameterSub-frame

Code tablePara Sub-frame

Para Frame

20 ms

Refresh20 ms

( Fixed)

Refresh

Refresh

Data rate

Data rate

NoiseSelf-adaptive

Threshold

LPC Filter parameter

Sub-frameVoice

Q-CELP CodingM

ultiplex

Channel

Page 28: CDMA Key Technology

Thank you


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