上行PRACH同步过程 - 图文

1.1 上行RACH信道知识

1.1.1

上行RACH信道作用

上行PRACH信道(Physical Random Access channel)上行随机接入信道,用于UE与网格侧的目标小区进行初始通信的第一条消息内容,其主要作用就是获取目标小区的上行同步.

1.1.2 上行RACH信道资源preamble原理

手机要取得与UE的上行同步,手机就要在PRACH信道上进行上行同步,然而上行同步是手机通过发送上行同步码来获得的.每个小区都有64个上行同步码,在相同的频率情况下,如果两个小区的上行同步码相同,就会产生严重的上行同步干扰,就无法成功获得上行同步.

那Preamble码是由什么产生的呢,协议定义了两种ZC序列(长度分别为839bit和139bit),前面讲PSS的ZC序列的特性时,ZC序列具有很好的自相关性和互相关性.任意两条ZC序列都是相互正交无干扰的.

这两种ZC序列的长度为839bit时,其preamble format(Preamble格式)为0~3,preamble format与小区覆盖半径有关.

Preamble format (table 5.7.2-1) 0 – 3 NZC指preamble的长度 839，序列个数=长度-1=838个 4 139，序列个数=长度-1=138个 Preamble format 0 1 2 3 4 TCP(us) 103 684 203 684 15 Tpreamble-sequence(us) 800 800 1600 1600 133 TGT(us) 100 520 200 720 9 总时长 小区覆盖距离(km) 1ms 2ms 2ms 3ms 157us 14 77 29 100 1.4 Preamble format的格式与小区半径的关系如下:以format0以例: 小区半径=min(GT,CP}*光速/2=min(103us,100us)*光速/2=100*10^(-6)*3*10^8/2=150000=15km

参数ra-PreambleIndex/root-SequenceIndex:preamble的root sequence index索引编号，当PRACH格式为0～3时，根序列为0～837，其838个，分为32个大的逻辑组，每个逻辑索引唯一对应一个物理序列；当PRACH格式为4时，根序列为0～137，其138个，分为7个逻辑组, 每个逻辑索引也是唯一对应一个物理序列；由小区配置可用的preamble sequence-index编号，在SIB中广播，一般小区每隔8使用一个根序列（rootsequence重新排序得到逻辑号，考虑preamble的峰均比）, 排序规律：每两个每对相加=839.

Preamble逻Preamble物理根序列号索引u(按逻辑根序列号升序排列) Format0～3 (36.211 table5.7.2-4) 辑根序列号索引 0–23 129, 710, 140, 699, 120, 719, 210, 629, 168, 671, 84, 755, 105, 734, 93, 746, 70, 769, 60, 779, 2, 837, 1, 838 24–29 30–35 36–41 42–51 52–63 64–75 56, 783, 112, 727, 148, 691 80, 759, 42, 797, 40, 799 35, 804, 73, 766, 146, 693 31, 808, 28, 811, 30, 809, 27, 812, 29, 810 24, 815, 48, 791, 68, 771, 74, 765, 178, 661, 136, 703 86, 753, 78, 761, 43, 796, 39, 800, 20, 819, 21, 818 76–89 90–115 95, 744, 202, 637, 190, 649, 181, 658, 137, 702, 125, 714, 151, 688 217, 622, 128, 711, 142, 697, 122, 717, 203, 636, 118, 721, 110, 729, 89, 750, 103, 736, 61, 778, 55, 784, 15, 824, 14, 825 116–135 136–167 12, 827, 23, 816, 34, 805, 37, 802, 46, 793, 207, 632, 179, 660, 145, 694, 130, 709, 223, 616 228, 611, 227, 612, 132, 707, 133, 706, 143, 696, 135, 704, 161, 678, 201, 638, 173, 666, 106, 733, 83, 756, 91, 748, 66, 773, 53, 786, 10, 829, 9, 830 168–203 7, 832, 8, 831, 16, 823, 47, 792, 64, 775, 57, 782, 104, 735, 101, 738, 108, 731, 208, 631, 184, 655, 197, 642, 191, 648, 121, 718, 141, 698, 149, 690, 216, 623, 218, 621 204–263 152, 687, 144, 695, 134, 705, 138, 701, 199, 640, 162, 677, 176, 663, 119, 720, 158, 681, 164, 675, 174, 665, 171, 668, 170, 669, 87, 752, 169, 670, 88, 751, 107, 732, 81, 758, 82, 757, 100, 739, 98, 741, 71, 768, 59, 780, 65, 774, 50, 789, 49, 790, 26, 813, 17, 822, 13, 826, 6, 833 264–327 5, 834, 33, 806, 51, 788, 75, 764, 99, 740, 96, 743, 97, 742, 166, 673, 172, 667, 175, 664, 187, 652, 163, 676, 185, 654, 200, 639, 114, 725, 189, 650, 115, 724, 194, 645, 195, 644, 192, 647, 182, 657, 157, 682, 156, 683, 211, 628, 154, 685, 123, 716, 139, 700, 212, 627, 153, 686, 213, 626, 215, 624, 150, 689 328–383 225, 614, 224, 615, 221, 618, 220, 619, 127, 712, 147, 692, 124, 715, 193, 646, 205, 634, 206, 633, 116, 723, 160, 679, 186, 653, 167, 672, 79, 760, 85, 754, 77, 762, 92, 747, 58, 781, 62, 777, 69, 770, 54, 785, 36, 803, 32, 807, 25, 814, 18, 821, 11, 828, 4, 835 384–455 3, 836, 19, 820, 22, 817, 41, 798, 38, 801, 44, 795, 52, 787, 45, 794, 63, 776, 67, 772, 72 767, 76, 763, 94, 745, 102, 737, 90, 749, 109, 730, 165, 674, 111, 728, 209, 630, 204, 635, 117, 722, 188, 651, 159, 680, 198, 641, 113, 726, 183, 656, 180, 659, 177, 662, 196, 643, 155, 684, 214, 625, 126, 713, 131, 708, 219, 620, 222, 617, 226, 613 456–513 230, 609, 232, 607, 262, 577, 252, 587, 418, 421, 416, 423, 413, 426, 411, 428, 376, 463, 395, 444, 283, 556, 285, 554, 379, 460, 390, 449, 363, 476, 384, 455, 388, 451, 386, 453, 361, 478, 387, 452, 360, 479, 310, 529, 354, 485, 328, 511, 315, 524, 337, 502, 349, 490, 335, 504, 324, 515 514–561 323, 516, 320, 519, 334, 505, 359, 480, 295, 544, 385, 454, 292, 547, 291, 548, 381, 458, 399, 440, 380, 459, 397, 442, 369, 470, 377, 462, 410, 429, 407, 432, 281, 558, 414, 425, 247, 592, 277, 562, 271, 568, 272, 567, 264, 575, 259, 580 562–629 237, 602, 239, 600, 244, 595, 243, 596, 275, 564, 278, 561, 250, 589, 246, 593, 417, 422, 248, 591, 394, 445, 393, 446, 370, 469, 365, 474, 300, 539, 299, 540, 364, 475, 362, 477, 298, 541, 312, 527, 313, 526, 314, 525, 353, 486, 352, 487, 343, 496, 327, 512, 350, 489, 326, 513, 319, 520, 332, 507, 333, 506, 348, 491, 347, 492, 322, 517 630–659 330, 509, 338, 501, 341, 498, 340, 499, 342, 497, 301, 538, 366, 473, 401, 438, 371, 468, 408, 431, 375, 464, 249, 590, 269, 570, 238, 601, 234, 605 660–707 257, 582, 273, 566, 255, 584, 254, 585, 245, 594, 251, 588, 412, 427, 372, 467, 282, 557, 403, 436, 396, 443, 392, 447, 391, 448, 382, 457, 389, 450, 294, 545, 297, 542, 311, 528, 344, 495, 345, 494, 318, 521, 331, 508, 325, 514, 321, 518 708–729 346, 493, 339, 500, 351, 488, 306, 533, 289, 550, 400, 439, 378, 461, 374, 465, 415, 424, 270, 569, 241, 598 730–751 231, 608, 260, 579, 268, 571, 276, 563, 409, 430, 398, 441, 290, 549, 304, 535, 308, 531, 358, 481, 316, 523 752–765 766–777 778–789 790–795 796–803 804–809 810–815 816–819 820–837 293, 546, 288, 551, 284, 555, 368, 471, 253, 586, 256, 583, 263, 576 242, 597, 274, 565, 402, 437, 383, 456, 357, 482, 329, 510 317, 522, 307, 532, 286, 553, 287, 552, 266, 573, 261, 578 236, 603, 303, 536, 356, 483 355, 484, 405, 434, 404, 435, 406, 433 235, 604, 267, 572, 302, 537 309, 530, 265, 574, 233, 606 367, 472, 296, 543 336, 503, 305, 534, 373, 466, 280, 559, 279, 560, 419, 420, 240, 599, 258, 581, 229, 610

PreamblePreamble物理根序列号索引u(按逻辑根序列号升序排列) Format4 (36.211 table5.7.2-5) 逻辑根序列号索引 0 – 19 20 – 39 40 – 59 60 – 79 80 – 99 1 138 2 137 3 136 4 135 5 134 6 133 7 132 8 131 9 130 10 129 11 128 12 127 13 126 14 125 15 124 16 123 17 122 18 121 19 120 20 119 21 118 22 117 23 116 24 115 25 114 26 113 27 112 28 111 29 110 30 109 31 108 32 107 33 106 34 105 35 104 36 103 37 102 38 101 39 100 40 99 41 98 42 97 43 96 44 95 45 94 46 93 47 92 48 91 49 90 50 89 100 – 119 51 88 120 – 137 61 78 52 87 62 77 53 86 63 76 54 85 64 75 55 84 65 74 56 83 66 73 57 82 67 72 58 81 68 71 59 80 69 70 60 79 - - PRACH的根序列产生公式：NZC是根ZC序列的长度,u为第u个根序列编号

?j?un(n?1)NZCxu?n??e循环移位

,0?n?NZC?1，然后通过xu,v(n)?xu((n?Cv)modNZC)这两种ZC序列,长度分别为839bit和139bit.这两种序列协议把它称为根序列

RootSequence,以839bit的序列为例,这种序列的个数=长度-1=838个.这838个序列中任意两个根序列都是相互正交和无干扰的.拿其中任何一个序列,由于序列上有839个点,选择任意一个点作为起点逆时针转一圈,都能得到一条序列,这样一条序列就叫一个Preamble,那总共838个根序列,每个根序列上有839个点,故每条根序列能产生839条Preamble,则总共的Preamble总数=838*839=703082条Preamble.任意两条Preamble都是相互正交和无干扰的.

参数

NCS:也是与小区覆盖半径决定的,比如小区覆盖半径为14公里时,Ncs索引取值一般可以是

11(12.52KM)或10(10.09KM),它是Preamble的Cyclic shift，目前只支持非限制集，限制集只适用于高速场景。若取值为11，则表示在此圆上每隔93个点取一个,每两个循环移位间隔为93,由于长度为839，因此这条根序列能产生=int(839/9)=9，即一条根序列可产生9个preamble，

NN因此需要ubound(64/9)=8个根序列，因此规划时每小区的root-sequence差8，CS=11。CS的大小决定小区半径，例取11，则小区半径={93*preamble时长/preamble长度/2}=800us*间隔93*C光速/839/2=13.3km，其中800us*间隔93就是指间隔的时延。

NCS 配置(preamble format4见36.211 table5.7.2-3) 0 1 NCS值 2 4

2 3 4 5 6 6 8 10 12 15 1.1.3 上行RACH信道资源preamble种类个数及划分细则

每个小区都有64(编号为0~63)个Preamble码,协议把它划分为2组,用于UE与网络侧的随机接入同步过程.一组是网络侧eNB指定分配给UE的preamble码,这种称为专用或非竞争的,这个码其它用户不能使用;另一组是UE自已随机选的,大家都可以用,这种称为竞争性的随机接入码.有参数指定随机接入码的个数numberOfRA-Preambles,此参数在SIB2中下发.如果此参数为48个(编号为0~47),则剩下的就是专用的Preamble码(48~63).同时协议又将竞争的分为GroupA和GroupB两组.具体如下图:

如果是竞争性的Preamble,那到底选用GroupA还是GroupB呢?在此需要提醒一下,假如eNB在随机接入用户同时很多的时候,eNB对GroupB比GroupA的优先级要高点.因此eNB选择GroupB时,需满足两个条件:

1).UE的信号要好,这样才能保证优先处理时的可靠性更高(链路损耗要小些) pathloss

pathlossThreshold=Pmax- preambleInitialReceivedTargetPower – deltaPreMsg3–messagePowerOffsetGroupB 2).手机中有较大的上行数据块要发送

(preamble中需要承载的消息量+MAC header大小)> messageSizeGroupA,有些厂家将此参数写为(raSmallVolUl)

1.1.4 上行RACH信道资源preamble频域位置

前面讲过,PRACH资源占频域的上行6个PRB,fomat0~3格式的Preamble的长度为839bit, 每个子载波的带宽为1.25KHZ, 则占用频域带宽为=7.5KHZ*839=1.048M,占用连续6个PRB(1.08M)的带宽;长度为139bit的Preamble的子载波的带宽为7.5JHZ,则同样占用7.5KHZ*139=1.0425M(连续6个PRB)的带宽.

在20MHZ的带宽下,上行总共有100个PRB,那PRACH到底在哪几个PRB呢.这与PRACHConfigIndex和上下行子帧配置有关.参数PRACHConfig是指PRACH的format格式,其中包含了一个无线帧内PRACH信道的个数(称为PRACH密度Density,1代表每无线帧出现一次,0.5代表第2个无线帧出现一次,其它按此类推).

PRACH configuration Index Preamble Format Density (Per10 msDRA) Version PRACH configuration Index 0 1 2 3（目前配置） 0 0 0 0 0.5 0.5 0.5 1(preamble时长1ms) 4 5 0 0 1 1 1 2 36 37 2 2 3 4 0 0 0 1 2 0 32 33 34 35 2 2 2 2 Preamble Format Density (Per10 ms Version VRA VRA DRA) 0.5 1 1 2 2 0 1 0 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 0.5 0.5 0.5 1 1 2 3 4 5 6 0 1 2 0 1 2 0 1 2 0 1 2 0 1 0 1 2 0 1 0 0 0 0 0 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 2 2 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 N/A N/A N/A N/A 5 6 0.5 0.5 0.5 1 1 2 3 4 0.5 0.5 0.5 1 1 2 3 4 5 6 N/A N/A N/A N/A 0 0 0 1 2 0 1 0 0 0 0 1 2 0 1 0 0 0 0 0 N/A N/A N/A N/A 30 31 2 2 0.5 0.5 0 1 62 63 N/A N/A N/A N/A N/A N/A

PRACH configuration Index (See Table 5.7.1-3) TDD PRACH的时间的频域位置UL/DL configuration (See Table 4.2-2) 0 0 1 2 3 4 5 6 7 (0,1,0,2) (0,2,0,2) (0,1,1,2) (0,0,0,2) (0,0,1,2) (0,0,0,1) (0,0,0,2) (0,0,1,2) (0,0,0,1) (0,0,1,1) 8 9 (0,0,0,0) (0,0,1,0) (0,0,0,1) (0,0,0,2) (0,0,1,2) 10 (0,0,0,0) (0,0,1,0) (0,0,1,0) (0,0,1,1) 11 N/A (0,0,1,1) (0,0,0,0) (0,0,0,1) (0,0,1,0) 12 (0,0,0,1) (0,0,0,2) (0,0,1,1) (0,0,1,2) 13 (0,0,0,0) (0,0,0,2) (0,0,1,0) (0,0,1,2) 14 (0,0,0,0) (0,0,0,1) (0,0,1,0) (0,0,1,1) N/A N/A (0,0,0,0) (0,0,0,1) (0,0,1,0) (0,0,1,1) N/A (0,0,0,0) (0,0,1,0) (1,0,0,0) (1,0,1,0) N/A (0,0,0,0) (0,0,0,1) (0,0,0,2) (1,0,0,2) (0,0,0,0) (0,0,0,1) (0,0,0,2) (1,0,0,1) (0,0,0,0) (0,0,0,1) (0,0,0,2) (1,0,0,0) N/A N/A (0,0,0,0) (0,0,0,1) (1,0,0,0) (1,0,0,1) N/A (0,0,0,0) (1,0,0,0) (2,0,0,0) (3,0,0,0) N/A (0,0,1,0) (1,0,1,0) N/A N/A (0,0,0,1) (1,0,0,0) N/A N/A (0,0,0,0) (0,0,0,1) (0,0,1,1) (0,0,0,1) (0,0,0,0) (0,0,1,0) (1,0,0,0) (0,0,0,0) 1 (0,1,0,1) (0,2,0,1) (0,1,1,1) (0,0,0,1) (0,0,1,1) (0,0,0,0) (0,0,0,1) (0,0,1,1) (0,0,0,0) (0,0,1,0) N/A N/A 2 (0,1,0,0) (0,2,0,0) (0,1,1,0) (0,0,0,0) (0,0,1,0) N/A (0,0,0,0) (0,0,1,0) N/A 3 (0,1,0,2) (0,2,0,2) (0,1,0,1) (0,0,0,2) (0,0,0,1) (0,0,0,0) (0,0,0,1) (0,0,0,2) (0,0,0,0) (0,0,0,2) (0,0,0,0) (0,0,0,1) (0,0,0,0) (0,0,0,1) (0,0,0,2) N/A (0,0,0,0) (0,0,0,1) (1,0,0,1) (0,0,0,0) (0,0,0,0) (1,0,0,0) (2,0,0,0) N/A N/A N/A 4 (0,1,0,1) (0,2,0,1) (0,1,0,0) (0,0,0,1) (0,0,0,0) N/A (0,0,0,0) (0,0,0,1) N/A 5 (0,1,0,0) (0,2,0,0) N/A (0,0,0,0) N/A N/A (0,0,0,0) (1,0,0,0) N/A 6 (0,1,0,2) (0,2,0,2) (0,1,1,1) (0,0,0,2) (0,0,1,1) (0,0,0,1) (0,0,0,2) (0,0,1,1) (0,0,0,1) (0,0,1,0) (0,0,0,0) (0,0,1,1) (0,0,0,1) (0,0,0,2) (0,0,1,1) (0,0,0,0) (0,0,0,2) (0,0,1,0) (0,0,0,1) (0,0,1,0) (0,0,1,1) (0,0,0,1) (0,0,0,2) (0,0,1,0) (0,0,1,1) (0,0,0,0) (0,0,0,1) (0,0,0,2) (0,0,1,1) (0,0,0,0) (0,0,0,2) (0,0,1,0) (0,0,1,1) 15 (0,0,0,0) (0,0,0,1) (0,0,0,2) (0,0,1,1) (0,0,1,2) (0,0,0,0) (0,0,0,1) (0,0,1,0) (0,0,1,1) (1,0,0,1) (0,0,0,0) (0,0,0,1) (0,0,1,0) (0,0,1,1) (1,0,1,1) (0,0,0,0) (0,0,0,1) (0,0,1,0) (0,0,1,1) (1,0,0,0) (0,0,0,0) (0,0,0,1) (0,0,1,0) (0,0,1,1) (1,0,0,1) (1,0,1,1) (0,0,0,0) (0,0,0,1) (0,0,1,0) (0,0,1,1) (1,0,0,0) (1,0,1,0) (0,0,0,0) (0,0,1,0) (1,0,0,0) (1,0,1,0) (2,0,0,0) (0,0,0,0) (0,0,1,0) (1,0,0,0) (1,0,1,0) (2,0,1,0) N/A (0,0,0,0) (0,0,0,1) (0,0,0,2) (1,0,0,1) (1,0,0,2) (0,0,0,0) (0,0,0,1) (0,0,0,2) (1,0,0,0) (1,0,0,2) (0,0,0,0) (0,0,0,1) (0,0,0,2) (1,0,0,0) (1,0,0,1) (0,0,0,0) (0,0,0,1) (1,0,0,0) (1,0,0,1) (2,0,0,1) (0,0,0,0) (0,0,0,1) (1,0,0,0) (1,0,0,1) (2,0,0,0) N/A (0,0,0,0) (1,0,0,0) (2,0,0,0) (3,0,0,0) (4,0,0,0) N/A (0,0,0,0) (0,0,0,1) (0,0,0,2) (0,0,1,0) (0,0,1,1) N/A 16 (0,0,0,1) (0,0,0,2) (0,0,1,0) (0,0,1,1) (0,0,1,2) 17 (0,0,0,0) (0,0,0,1) (0,0,0,2) (0,0,1,0) (0,0,1,2) N/A N/A 18 (0,0,0,0) (0,0,0,1) (0,0,0,2) (0,0,1,0) (0,0,1,1) (0,0,1,2) (0,0,0,0) (0,0,1,0) (1,0,0,0) (1,0,1,0) (2,0,0,0) (2,0,1,0) N/A (0,0,0,0) (0,0,0,1) (0,0,0,2) (1,0,0,0) (1,0,0,1) (1,0,0,2) N/A (0,0,0,0) (0,0,0,1) (1,0,0,0) (1,0,0,1) (2,0,0,0) (2,0,0,1) N/A (0,0,0,0) (1,0,0,0) (2,0,0,0) (3,0,0,0) (4,0,0,0) (5,0,0,0) N/A (0,0,0,0) (0,0,0,1) (0,0,0,2) (0,0,1,0) (0,0,1,1) (1,0,0,2) (0,0,0,0) (0,0,0,1) (0,0,0,2) (0,0,1,0) (0,0,1,1) (1,0,1,1) 19 N/A 20 / 30 21 / 31 22 / 32 23 / 33 24 / 34 25 / 35 (0,1,0,1) (0,2,0,1) (0,1,1,1) (0,0,0,1) (0,0,1,1) (0,0,0,1) (0,0,1,1) (0,1,0,0) (0,2,0,0) (0,1,1,0) (0,0,0,0) (0,0,1,0) (0,0,0,0) (0,0,1,0) (0,0,0,0) (0,0,1,0) (1,0,0,0) (0,0,0,0) (0,0,1,0) (1,0,0,0) (1,0,1,0) (0,0,0,0) N/A N/A N/A N/A N/A N/A (0,1,0,1) (0,2,0,1) N/A (0,0,0,1) N/A (0,0,0,1) (1,0,0,1) (0,1,0,0) (0,2,0,0) N/A (0,0,0,0) N/A (0,0,0,0) (1,0,0,0) (0,0,0,0) (1,0,0,0) (2,0,0,0) (0,0,0,0) (1,0,0,0) (2,0,0,0) (3,0,0,0) (0,0,0,0) N/A N/A N/A N/A N/A N/A (0,1,0,1) (0,2,0,1) (0,1,1,0) (0,0,0,1) (0,0,1,0) (0,0,0,1) (0,0,1,0) 26 / 36 (0,0,0,1) (0,0,1,1) (1,0,0,1) N/A (0,0,0,1) (1,0,0,1) (2,0,0,1) (0,0,0,1) (1,0,0,1) (2,0,0,1) (3,0,0,1) (0,0,0,1) N/A (0,0,0,1) (0,0,1,0) (1,0,0,1) (0,0,0,1) (0,0,1,0) (1,0,0,1) (1,0,1,0) (0,0,0,1) N/A N/A 27 / 37 (0,0,0,1) (0,0,1,1) (1,0,0,1) (1,0,1,1) 28 / 38 (0,0,0,1)

(0,0,1,1) (1,0,0,1) (1,0,1,1) (2,0,0,1) 29 /39 (0,0,0,1) (0,0,1,1) (1,0,0,1) (1,0,1,1) (2,0,0,1) (2,0,1,1) 40 41 42 43 44 45 (0,1,0,0) (0,2,0,0) (0,1,1,0) (0,0,0,0) (0,0,1,0) (0,0,0,0) (0,0,1,0) 46 (0,0,0,0) (0,0,1,0) (1,0,0,0) 47 (0,0,0,0) (0,0,1,0) (1,0,0,0) (1,0,1,0) 48 49 50 51 52 53 54 (0,1,0,*) (0,2,0,*) (0,1,1,*) (0,0,0,*) (0,0,1,*) (0,0,0,*) (0,0,1,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) 55 (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) 56 (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (2,0,0,*) (0,0,1,0) (1,0,0,0) (1,0,1,0) (2,0,0,0) (0,0,0,0) (0,0,1,0) (1,0,0,0) (1,0,1,0) (2,0,0,0) (2,0,1,0) N/A N/A N/A N/A N/A N/A N/A (1,0,0,1) (2,0,0,1) (3,0,0,1) (4,0,0,1) (0,0,0,1) (1,0,0,1) (2,0,0,1) (3,0,0,1) (4,0,0,1) (5,0,0,1) (0,1,0,0) (0,2,0,0) N/A (0,0,0,0) N/A (0,0,0,0) (1,0,0,0) (1,0,0,0) (2,0,0,0) (3,0,0,0) (4,0,0,0) (0,0,0,0) (1,0,0,0) (2,0,0,0) (3,0,0,0) (4,0,0,0) (5,0,0,0) N/A N/A N/A N/A N/A N/A N/A (0,0,1,0) (1,0,0,1) (1,0,1,0) (2,0,0,1) (0,0,0,1) (0,0,1,0) (1,0,0,1) (1,0,1,0) (2,0,0,1) (2,0,1,0) (0,1,0,0) (0,2,0,0) N/A (0,0,0,0) N/A (0,0,0,0) (1,0,0,0) N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A (0,0,0,0) (1,0,0,0) (2,0,0,0) (0,0,0,0) (1,0,0,0) (2,0,0,0) (3,0,0,0) (0,1,0,*) (0,2,0,*) N/A (0,0,0,*) N/A (0,0,0,*) (1,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (4,0,0,*) N/A N/A (0,0,0,0) (1,0,0,0) (2,0,0,0) (0,0,0,0) (1,0,0,0) (2,0,0,0) (3,0,0,0) (0,1,0,*) (0,2,0,*) (0,1,1,*) (0,0,0,*) (0,0,1,*) (0,0,0,*) (0,0,1,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (2,0,0,*) N/A N/A N/A N/A (0,1,0,*) (0,2,0,*) (0,1,1,*) (0,0,0,*) (0,0,1,*) (0,0,0,*) (0,0,1,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (2,0,0,*) (0,1,0,*) (0,2,0,*) (0,1,1,*) (0,0,0,*) (0,0,1,*) (0,0,0,*) (0,0,1,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (2,0,0,*) (0,1,0,*) (0,2,0,*) N/A (0,0,0,*) N/A (0,0,0,*) (1,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (4,0,0,*) (0,1,0,*) (0,2,0,*) N/A (0,0,0,*) N/A (0,0,0,*) (1,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (4,0,0,*) 57 (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (2,0,0,*) (2,0,1,*) (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (2,0,0,*) (2,0,1,*) N/A N/A N/A N/A N/A N/A (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (2,0,0,*) (2,0,1,*) N/A N/A N/A N/A N/A N/A (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (4,0,0,*) (5,0,0,*) N/A N/A N/A N/A N/A N/A (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (4,0,0,*) (5,0,0,*) N/A N/A N/A N/A N/A N/A (0,0,0,*) (1,0,0,*) (2,0,0,*) (3,0,0,*) (4,0,0,*) (5,0,0,*) N/A N/A N/A N/A N/A N/A (0,0,0,*) (0,0,1,*) (1,0,0,*) (1,0,1,*) (2,0,0,*) (2,0,1,*) N/A N/A N/A N/A N/A N/A 58 59 60 61 62 63 N/A N/A N/A N/A N/A N/A 以PRACHconfigIndex=3和上下行子帧配置=2(1:3)为例,其交集为(0,0,0,0).

组合中(0,0,0,0),第一个0就是指PRACH的频域的位置RA的值,在此组合中为0, .其频域真正位置为

RAnPRB.

fRAnPRB?RA?fRA?n?6*if fRAmod2?0?PRB offset?2?,?????

?fRA?ULRA?NRB?6?nPRB?6*,otherwise offset????2??RARA由于fRA=0,因此nPRB=nPRB offset?f?RA?0?=nRA?6*?RA?=nPRB?6*PRB offset offset??22????参数nPRB offset就是指PRACH信道离带宽两端边界的PRB编号0或100的偏离位置,如果PRACH在带宽底端,且要占用6个PRB,则nPRB offset=5(PRAB编号0~5,共6个PRB是PRACH信;);如果PRACH在带宽顶端,且要占用6个PRB,则nPRB offset=94(PRAB编号94~99,共6个PRB是PRACH信道).

RARARA因为考虑到上行SC-FDMA的特性,上行PUSCH必须要参够连续且可以过到最大的峰值速率,因此协议规定PRACH只能位于带宽的两端.

1.1.5 上行RACH信道资源preamble时域位置

前面讲PRACH频域位置时讲过,PRACH的频域位置与PRACHconigIndex/上下行子帧配置/参数

RAnPRB offset这3个因素决定.同样以PRACHConfigIndex=3且上行下子帧配置为2时,还是组合

(0,0,0,0),那这个组合不仅决定了PRACH的PRACH的频域位置,也同样决定PRACH的时域位置.具体是此组合的后面3个值决定了PRACH的时域位置.对应(RA,RA1)(2)ft(0),t(tRA) RA, 组合(0,0,0,0)中第2个0是对应RA的值,值0表示每个无线帧中都是PRACH

t(0)t(1)组合(0,0,0,0)中第3个0是对应RA的值,值0表示前半帧中有PRACH

组合(0,0,0,0)中第4个0是对应RA的值,值0表示前半帧的第一个上行子帧有PRACH(即上行子帧

t(2)2)

因此组合(0,0,0,0)的意思是:PRACH出现在每个无线帧中的前半帧的上行子帧2中.

1.1.6 上行RACH信道的同步原理过程

UE在上行随机接入过程中,要发送上行同步码,到时是选择竞争性的或非竞争性的Preamble将根据场景决定.

?

只能使用竞争性的Preamble有以下5种场景

?

UE MAC层自身触发的随机接入过程

如:UE自已要做业务(打电话或上网,从Idle状态发起随机接入);这种称为MAC自身触发的随机接入.因为随机接入过程在MAC层选择相应的随机接入参数(如preambleIndex具体Preamble编号,Preamble的功率等),且在MAC层中检测随机接入响消息,因此随机接入过程是在MAC层处理的. ?

UE有上行数据要发,但UE发现上行此时处理失步状态,如果此时发送上行数

据将会失败,因此要做上行随机接入过程.

?

UE发现下行失步,如果出现了下行失步,但eNB此时还不知道的情况下如果

eNB发送下行数据,此时UE就会收不到下行数据包.因此UE需要重新进行上行同步,只有同步成功后才能继续保持上下行链路数据的正常传输.

? 在连接状态下,UE如果此时有数据要发送上行调度请求SR(shecudle

request),请求eNB分配上行PUSCH资源.但若此时上行没有SR资源可用,且上行也没有可以使用的PUCCH或PUSCH资源,此时UE要通过上行随机接入过程告诉eNB,请求分配上行资源.

?

UE在发起RRC重建的过程中会进行上行随机接入.

?

一般情况下,使用专用的(非竞争性)Preamble有以下2种场景,这种情况协议称为PDCCH order触发的随机接入,就是指网络侧通过RRC重配命令告诉UE要去做随机接入过程.

?

切换过程

在切换过程中,一般情况下eNB会从专用的preamble中选择一个未使用的preamble分配给某个UE,其具体编号preambleIndex在RRC重配消息中下发.

? eNB有下行数据要发,此时发现UE是处于上行失步状态,因此eNB要通知UE,

告诉UE上行是失步的,并且要求UE重新做随机接入,此时一般也会分配专用的Preamble给UE,更可靠地保证UE的上行随机接入的成功率.

?

在RRC连接状态下,eNB需要对UE进行位置position定位时,需要通知UE

进行随机接入.

同时协议还规定,使用专用Preamble的场景中,eNB也可以不分配专用的Preamble,通知UE时让UE自已选择竞争性的Preamble来进行随机接入.

另外,UE在发送完Preamble后,会在接下来的一段时间内监听随机接入响应消息.这段时间是参数RadomAceessResponseWindowSize(随机接入响应的监测窗口时间),其具体监测的时间3个子帧后的RadomAceessResponseWindowSize的时间内.假

设:RadomAceessResponseWindowSize=10ms.假设UE在子帧在发送了RA,则在子帧5~下一个无线帧的子帧4这10ms的下行子帧中监听RAR消息.

1.1.6.1 上行RACH信道preamble的选择知识

UE在上行进行随机接入的时候,如果采用竞争性的随机接入过程,则UE会根据自身的情况从选择GroupA或GroupB中随机选择一个Preamble,如果此次Preamble同步失败,则UE再次选择时只能从之前的相同的组中剩余的Preamble中再随机选择一个.

如果是专用式的随机接入,则UE会一直使用这个eNB分配的Preamble做随机接入,直到随机接入成功或达到最大次数后的随机接入失败为止.

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