1、1中国移动无线竞赛故障排除（4）一简答题1 请简述误码率产生的原因。a. 低信噪比；b. 信号抖动；码间干扰。2. 请简述基带跳频的原理和作用。答案：跳频用来减少无线干扰。原理如图：承载同一用户的相同时隙，按照帧结构，在不同的载频上以事先定义的跳频规律传送。Frame 0 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5TCHRFC 1RFC 2RFC 3RFC 4RFC 5TDMA Frame23. 请简述基带跳频和合成跳频的不同。 4. 同一用户的业务，基带跳频每一帧用不同收发信机的不同载频承载，而合成跳频用同一收发信机不断改变发信频率来实现。请简述设定 PC
2、MB 链路时参数的含义：PCM30:HDB3:CRC4:BER=10E-3 to10E-6：PCM30:脉冲编码调制，每一帧 30 个话务时隙HDB3: 编码方式CRC4: 循环冗余校验BER=10E-3 to10E-6：误码率5. BTS 中哪些信道可能过载? 请简述缓解 AGCH 的过载都有哪些手段。TCH overload, SDCCH overload, AGCH overload, PCH overload.To reduce the AGCH overload: 1) increase the LU size of the network; 2) discard the pagin
3、g messages of the cell; 3) decrease the MOC of the cell; 4) increase CCCH number.二分析题31.下图为 GSM 的物理信道的复帧结构，请回答以下问题：RFC1RFC27654321RFC30TDMAFrameFDMATimetFrequency0123456464748495001234562425BCH-MultiframeTCH-MultiframeRFC1741) GSM 采用了什么多址接入技术？2) 每个载频带宽多少？174 个 RFC 需要占用多大的频率带宽？3)TDMA 帧结构中，业务复帧由和信令复帧各
4、由多少帧 组成？44)每个 TDMA 帧有多少个时隙？5) BCCH 通常放在哪个时隙？(1) FDMA+TDMA(2) 200kHz(174+1)*200KHz=35MHz(3) 26,51(4) 8(5) 0 时隙52.下图为基带跳频的示意图。Frame 0 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5TCHRFC 1RFC 2RFC 3RFC 4RFC 5TDMA Frame1）跳频有什么作用？2）根据上图说明基带跳频的原理：3）请找出图中的一处错误。) 降低无线干扰(2) 同一用户的业务，基带跳频每一帧用不同收发信机的不同载频承载，(3) RF4 上的
5、 Frame1 应为 TS5。（实际上 Frame1 多画了一个时隙）3.下图为逻辑信道树：6CHANELSUL+DL UL+DL DL DL UL UL + DLTRAFICCHNELS SIGNALINGCHELSBROADCASTCNTROLHALES DEICATEDCONROLHALESFULRATE HALFRTE COMONNTRLCHALES_1_TCH/ _2_FCHSCHPCH NCH _3_RACHSACH_4_FACH1） 请将信道树上空出位置填满：1:2:3:4:2） BSC 数据库中 MAINBCCH 的信道组合是：MAINBCCHBCCH+_+_+_73） 逻辑信
6、道中那些信道只有上行？那些信道只有下行？1: TCH/F2: BCCH3: AGCH4: SDCCH(2) MAINBCCHBCCH+FCCH+SCH+CCCH(3)Only UL:RACHOnly DL:AGCH, BCCH， PCH，FCCH ，SCH ，NCH84. 下图为位置更新的信令流程：Location updateCh.1? Chanel Request(Reason = Loc. Upd., Random Reference)UI (Imediate Asignment)(Request Reference, SDCH-No.) Ch.2?Ch.3? SABM (Locatio
7、n Update Request)(TMSI + old LAI, CKSN, loc upd. type)SDCHUA SDCHI (Authentication Request)(RAND, CKSN)SDCH I (Authentication Response) (SRES)SDCHI (Ciphering Mode Comand)SDCH I (Ciphering Mode Complete)SDCHI (LocationUpdate Acept) (newTMSI, newLAI)SDCH I (TMSI Realocation Complete)SDCHI (ChanelRele
8、ase)SDCH DISCSDCHUA1）Ch.1,Ch.2,Ch.3 分别是什么信道？92）根据上图解释鉴权的过程。3）位置更新中 SDCCH 采用信道加密模式有什么作用？4）上图流程中，空中接口第二层采用了哪些类型的 LAPD 帧？1) RACH, AGCH, SDCCH(2) 三参数，略。(3) 保证空中接口安全传送 TMSI 和 LAI 数据。(4) I, UI，SABM，DISC，UA 等 LAPD 帧。5. 结合简图说明 RC 与 BSC 之间的连接方式。1)Connection via PCM- Links10BSC TRAUMSCOMC PerformanceTechnolgy
9、NUCNailed UpConectionPCM30 Link 64k TS PCM30 Link 64k TSTRAUBSC2) Connection via Dedicated Line11BSC IXLTOMC HSI/PPSDNX.25networkModem Modemdeicated pointopoint conectionconectionvia packet switched at networkX.21/ V.1 Interface1)Connection via PCM- LinksIn the BSC database an X25 connection and the
10、 OMC connection have to be created, using the commands CREATE:X25A and CREATE:OMAL.The OMAL (at a transmission rate of 64 kbit/s) is mapped on the BSC site in the PCMS Link, connecting BSC with TRAU and the MSC site.The OMAL is transferred through the TRAU transparently.At the MSC the incoming OMAL
11、of several incoming PCMA Links are multiplexed into a common 2 Mbit/s link (based on the PCM30 structure), which is directly connected with the OMC. This implementation is called “nailed up connection“. The OMC can control and supervise up to 48 BSS.This communication interface is implemented by a P
12、erformance Technology Card, equipped internal the OMP.2) Connection via Dedicated LineThe connection via dedicated line can be realized in two ways:12dedicated point to point linkconnection via a private or public Packet Switched Data NetworkAt the BSC site the interface is implemented on the IXLT b
13、oard and based on the X.21/ V.11 structure.At the OMC the interface is implemented by HSI/P card.In this configuration the OMC-B can control and supervise up to 48 BSS.The X.25 packet switched data network requires special modems to convert the X.21/ V.11 interface into the X.25 protocol, used at the packet switched data network.
