手机异常位置更新导致的立即指配成功率降低问题分析.doc

手机异常位置更新导致的立即指配成功率降低问题分析内部公开手机异常位置更新导致的立即指配成功率降低问题分析 1 问题现象描述部分少量手机异常位置更新导致立即指配成功率降低，网络中业务（主被叫、数据业务及附加业务等）均正常。问题手机位置更新未成功的情况下，会不断地向其他小区发起位置更新直到成功为止。因此问题手机也不会发生掉网等情况，业务可正常进行。图1.1 BSC下出现立即指配成功率小区话统图1.2 立即指配成功率低小区话统变化情况2 问题原因部分手机不符合协议，导致无理由向网络发送位置更新请求，但是本身又不按照协议完成流程，造成立即指配命令下发后，空口无响应，立即指配流程失败。3 问题分析问题的关键在空口交互。3.1 位置更新（立即指配）流程正常位置更新流程：图1.3 正常位置更新流程问题发生时，异常信令流程(立即指配命令下发后没有SABM接入)：图1.4 异常位置更新流程异常信令流程实例：图1.5 异常信令流程实例3.2 信道请求Channel request（Acess Burst）3.2.1 Channel request（Aces Burst）协议规范空口手机MS以发送随机接入帧的方式，发起信道请求，协议对此有明确的结构（0502）和信道编码方式（0503）统一规定（位置更新的信令请求和其他的SDCCH信道请求）。1、0502协议对Acess Burst 结构的定义Access Burst主要由两部分组成：（1）41比特长度的synch. sequence bits（2）36比特长度的encrypted bits（实际是信道编码后比特数据，非加密过的比特数据）Bit Number(BN)Lengthof fieldContentsof fieldDefinition0 - 78extended tail bits(below)8 - 4841synch. sequence bits(below)49 - 8436encrypted bits (e0.e35)05.0385 - 873tail bits(below)(88 - 15668,25extended guard period (bits)subclause 5.2.8)where the extended tail bits are defined as modulating bits with the following states:(BN0, BN1, BN2 . BN7)= (0, 0, 1, 1, 1, 0, 1, 0)-where the tail bits are defined as modulating bits with the following states:(BN85, BN86, BN87)= (0, 0, 0)-where the synch. sequence bits are defined as modulating bits with the following states, unless explicitly stated otherwise (see GSM 04.60):(BN8, BN9 . BN48)=(0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0)in case alternative training (synchronization) sequence TS1 is used, the synch. sequence bits shall be defined as modulating bits with the following states: (BN8, BN9 . BN48)=(0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1)in case alternative training (synchronization) sequence TS2 is used, the synch. sequence bits shall be defined as modulating bits with the following states: (BN8, BN9 . BN48)=(1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1)2、0503协议中关于Access Burst encrypted bits 信道编码方式的描述编码过程如下：（1）8比特的接入信息先增加6比特的CRC校验比特（2）将目标基站的BSIC码和6比特的CRC校验比特异或（3）进行1/2的卷积编码，输出36比特encrypted bitsThe burst carrying the random access uplink message has a different structure. It contains 8 information bits d(0),d(1),.,d(7).Six parity bits p(0),p(1),.,p(5) are defined in such a way that in GF(2) the binary polynomial:d(0)D13 +.+ d(7)D6 + p(0)D5 +.+ p(5), when divided by D6 + D5 + D3 + D2 + D + 1 yields a remainder equal to 0.The six bits of the BSIC, B(0),B(1),.,B(5), of the BS to which the Random Access is intended, are added bitwise modulo 2 to the six parity bits, p(0),p(1),.,p(5). This results in six colour bits, C(0) to C(5) defined as C(k) = b(k) + p(k) (k = 0 to 5) where:b(0) = MSB of PLMN colour codeb(5) = LSB of BS colour code.This defines u(0),u(1),., u(17) by:u(k)= d(k)for k = 0,1,.,7u(k)= C(k-8)for k = 8,9,.,13u(k)= 0for k = 14,15,16,17 (tail bits)The bits e(0),e(1),., e(35) are obtained by the same convolutional code of rate 1/2 as for TCH/FS, defined by the polynomials:G0 = 1 + D3 + D4G1 = 1 + D + D3 + D4and with:e(2k)= u(k) + u(k-3) + u(k-4)e(2k+1)= u(k) + u(k-1) + u(k-3) + u(k-4)for k = 0,1,.,17 ; u(k) = 0 for k 03、GSM4.08协议信道请求具体含义：The message is only one octet long, coded as shown in figure 9.1/GSM4.08 and table9.9/GSM04.08. 8 7 6 5 4 3 2 1 ESTABLISHMENT RANDOM octet 1 CAUSE REFERENCE Figure 9.1/GSM04.08: CHANNEL REQUEST message content位置更新相关bit定义:Table 9.9/GSM04.08: CHANNEL REQUEST message contentMS codesAccording to Establishment cause:bits8 . 1101xxxxxEmergency call110xxxxxCall re-establishment; TCH/F was in use, orTCH/H was in use but the network does notset NECI bit to 1011010xxCall re-establishment; TCH/H was in use and thenetwork sets NECI bit to 1011011xxCall re-establishment; TCH/H + TCH/H was in useand the network sets NECI bit to 1100xxxxxAnswer to paging0010xxxx0011xxxxSee table9.9a/GSM04.080001xxxx111xxxxxOriginating call and TCH/F is needed, or originating calland the network does not set NECI bit to 1, orprocedures that can be completed with a SDCCH and thenetwork does not set NECI bit to 1.note 10100xxxxOriginating speech call from dualrate mobile station when TCH/His sufficient and supported by the MS for speech calls and the network sets NECI bit to 1note 50101xxxxOriginating data call from dualrate mobile station when TCH/His sufficient and supported by the MS for data calls and the network sets NECI bit to 1note 5000xxxxxLocation updating and the network does not set NECI bit to 10000xxxxLocation updating and the network sets NECI bit to 10001xxxxOther procedures which can be completed with note 1an SDCCH and the network sets NECI bit to 101100xxxReserved for future usenote 20111xxxx3.2.2 华为基站接收Acess Burst接入脉冲的过程BTS侧通过一系列措施可以保证解出的数据正确。（1）进行GMSK均衡，比较41比特训练序列错误比特数，若大于配置的RACH训练序列错误门限，则直接返回（进行干扰信号排查）（2）计算TA值，若大于配置的Max TA，则直接返回（3）计算信号电平，若小于配置的RACH最小接入电平，则直接返回（4）进行卷积译码（5）将BSIC和6比特CRC校验异或，然后进行CRC校验，若校验错，则直接返回（判断是给本小区发起的信道请求）（6）将当前帧号，译码后8比特接入信息通过Abis口信道接入请求消息上报给BSC3.3 立即指配3.3.1 手机正常行为模式1、 手机在发送信道请求之后进入专用模式，监听主B和所属CCCH组的所有下行时隙。GSM 0408:After sending the first CHANNEL REQUEST message, the mobile station shall start listening to the BCCH; it shall also listen to the full downlink CCCH timeslot corresponding to its CCCH group.Having sent M + 1 CHANNEL REQUEST messages, the RR entity of the mobile station starts timer T3126. At expiry of timer T3126, the immediate assignment procedure is aborted; if the immediate assignment procedure was triggered by a request from the MM sublayer, a random access failure is indicated to the MM sublayer.Table 3.1/GSM04.08: Values of parameter S TX-integer non combined CCCH combined CCH/SDCCH 3,8,14,50 55 41 4,9,16 76 52 5,10,20 109 58 6,11,25 163 86 7,12,32 217 115 2、 手机在收到立即指配命令后向指定信道发送SABM帧。3.3.2 问题时间段的异常流程BSS侧下发立即指配命令在等待手机接入过程中，基站测量到上行的信号强度一直为 -110dBm（基站测量），即手机根本没有去SDCCH上正常上报建链指示，导致立即指配过程失败。图1.6 手机未接入已分配信道3.4 现网问题情况分析手机发起位置更新但在收到立即指配后没有接入。3.4.1 手机上报异常上报信道请求（位置更新）1、 修改小区为小区接入禁止（CBA），小区的立即指配成功率恢复正常手机行为发起异常位置更新修改小区接入禁止参数（CBA）功能的原理：1 打开小区接入禁止(打开小区接入禁止)的情况下，在本小区的系统消息中携带标志位知会手机;图1.7 小区系统消息下发小区接入禁止属性2 收到系统消息的手机在进行小区重选时将不再会考虑此小区，转向其他小区进行位置更新。（打开小区接入禁止周围小区位置更新增加）。图1.8 话统 3：40：25s-3：52：12小区修改CBA2、 位置更新情况为高电平低误码，TA值（除部分覆盖范围较大站点以外）手机行为发起异常位置更新 图1.9 信道请求：TA为0或1，上行接入电平为1C或1D，即-72或-73dBm3、 同一个手机发起的位置更新请求次数符合现网参数设定异常位置更新是手机行为发起从手机上报的物理信息可以基本判断是同一手机。（附影响手机上报次数配置GSM 0408）位置更新的最大发送次数（5）：图1.10 手机连续发起信道请求消息参数配置（信道请求相关）： 图1.11 数据配置- MS最大重发次数为4次（M=4）图1.12 数据配置-其他 附（影响手机上报次数配置GSM 0408）：It then sends maximally M + 1 CHANNEL REQUEST messages on the RACH in a way such that:-the number of slots belonging to the mobile stations RACH between initiation of the immediate assignment procedure and the first CHANNEL REQUEST message (excluding the slot containing the message itself) is a random value drawn randomly for each new initial assignment initiation with uniform probability distribution in the set 0, 1, ., max (T,8)1;-the number of slots belonging to the mobile stations