CDMA Key Technology. ZTE Corporation CDMA Division

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 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.

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

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 on 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 interference FERs are measured instead of E/I

Power Control (3) Reverse Open Loop Power Control (Constant) Transmitting Power, Control range:±32 db MS Receiving Power Reverse Closed Loop Power Control BS Target E b / I o Power control algorithm Adjustment instruction MS Transmitting Power Information packet E b / I o Inner loop Adjustment of Target E/I Error rate algorithm Outer loop E b / I o

Power Control (4) Forward Link Power Control Transmitting Power Base Station FER MS

Power Control (Continued) Reverse Open Loop Reverse Open Loop Power Control Mobile BTS 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

Power Control (Continued) Reverse Closed Loop Mobile BTS or Reverse Closed Loop Power Control Signal Strength Measurement Setpoint 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

Power Control (Continued) Reverse Outer Loop Mobile BTS BSC or Reverse Closed Loop Power Control Signal Strength Measurement Setpoint Reverse Outer Loop Power Control FER Reverse Outer Loop Power Control Setpoint is varied according to FER on reverse link (measured at the Base Station Controller) Sampled at 50 frames per second rate (20msec) Setpoint adjusted every 1-2 seconds

Power Control (Continued) Stat. Backward link BS FER Outer-loop adjustment Closed-loop control measurement Eb Nt BS MS Transmit power adjustment Power control (bit) 1 =1%? Eb > Eb? Nt N 0 1% Outer loop adjustment algorithm, new Power control (bit) 0 Transmit Power Eb N 0 control command detection

Power Control (Continued) Forward Link Mobile BTS BSC FER Adjust Fwd. power Forward Link Power Control 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

Power Control (Continued) CDMA Power Control Summary Reverse Open Loop Power Control Mobile BTS BSC or Reverse Closed Loop Power Control Signal Strength Measurement Adjust Fwd. power FER Setpoint Reverse Outer Loop Power Control FER Forward Link Power Control All types of power control work simultaneously to minimize transmit power

Diversity Three types of diversity in CDMA. Time Diversity Frequency Diversity Space Diversity

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

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

Rake Receiver The rake receiver is a CDMA feature 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 multipath signals and combines them to produce one very strong signal. A Multi-path Propagation Rayleigh Fading λ /2 10-15 db t

Diversity (Continued) Time Diversity g 0 Output C 0 Input Convolutional g 1 C 1 g2 C 2 Interleaving 1 33 65 97 129 161 193 225 257 289 321 353 385 417 449 481 513 545 2 34 66 98 130 162 194 226 258 290 322 354 386 418 450 482 514 546 3 35 67 99 131 163 195 227 259 291 323 355 387 419 451 483 515 547 4 36 68 100 132 164 196 228 260 292 324 356 388 420 452 484 516 548 5 37 69 101 133 165 197 229 261 293 325 357 389 421 453 485 517 549 6 38 70 102 134 166 198 230 262 294 326 358 390 422 454 486 518 550 7 39 71 103 135 167 199 231 263 295 327 359 391 423 455 487 519 551 8 40 72 104 136 168 200 232 264 296 328 360 392 424 456 488 520 552 9 41 73 105 137 169 201 233 265 297 329 361 393 425 457 489 521 553 10 42 74 106 138 170 202 234 266 298 330 362 394 426 458 490 522 554 11 43 75 107 139 171 203 235 267 299 331 363 395 427 459 491 523 555 12 44 76 108 140 172 204 236 268 300 332 364 396 428 460 492 524 556 13 45 77 109 141 173 205 237 269 301 333 365 397 429 461 493 525 557 14 46 78 110 142 174 206 238 270 302 334 366 398 430 462 494 526 558 15 47 79 111 143 175 207 239 271 303 335 367 399 431 463 495 527 559 16 48 80 112 144 176 208 240 272 304 336 368 400 432 464 496 528 560 17 49 81 113 145 177 209 241 273 305 337 369 401 433 465 497 529 561 18 50 82 114 146 178 210 242 274 306 338 370 402 434 466 498 530 562 19 51 83 115 147 179 211 243 275 307 339 371 403 435 467 499 531 563 20 52 84 116 148 180 212 244 276 308 340 372 404 436 468 500 532 564 21 53 85 117 149 181 213 245 277 309 341 373 405 437 469 501 533 565 22 54 86 118 150 182 214 246 278 310 342 374 406 438 470 502 534 566 23 55 87 119 151 183 215 247 279 311 343 375 407 439 471 503 535 567 24 56 88 120 152 184 216 248 280 312 344 376 408 440 472 504 536 568 25 57 89 121 153 185 217 249 281 313 345 377 409 441 473 505 537 569 26 58 90 122 154 186 218 250 282 314 346 378 410 442 474 506 538 570 27 59 91 123 155 187 219 251 283 315 347 379 411 443 475 507 539 571 28 60 92 124 156 188 220 252 284 316 348 380 412 444 476 508 540 572 29 61 93 125 157 189 221 253 285 317 349 381 413 445 477 509 541 573 30 62 94 126 158 190 222 254 286 318 350 382 414 446 478 510 542 574 31 63 95 127 159 191 223 255 287 319 351 383 415 447 479 511 543 575 32 64 96 128 160 192 224 256 288 320 352 384 416 448 480 512 544 576

Diversity (Continued) Frequency Diversity Bandwidth of Traditional Signal : 200~300 KHz Bandwidth of CDMA Signal : 1.25MHz 50 times 1.25 MHz 200-300 KHz

Diversity (Continued) Space Diversity Rake Receiver Correlator Soft Handoff Diversity Antenna Correlator Correlator MS RX1 RX0 Diversity receiver is useful in reducing multipath fading

Soft Handoff Soft Handoff Softer Handoff Soft/Softer 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 makebefore-break. It reduces call drop.

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

Soft Handoff (2) M S C M S C B S C B S C B

Soft Handoff Process (3) Pilot Strength Ec/No BS A BS B Threshold r1 r2 Threshold BS C Hand off execution area Timing t1 t2 t3 t Soft Handoff from BS A to BS B

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

Voice Coding 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 64k PCM 13k GSM 8k CDMA 13k CDMA

Q-CELP Coding Data rate 8KHz 20 ms Tone parameter Sub-frame Refresh Voice Sampling 160 Sampled Value LPC Filter parameter Sub-frame Refresh 20 ms ( Fixed ) Multiplex Channel Code table Para Sub-frame Refresh Noise Self-adaptive Threshold Para Frame Data rate

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