电子类专业英语电子教案第三课.ppt

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1、概述第一代移动通信系统从80年代中期开始，以模拟传输和采用频分复用（FDMA）这样的简单复用技术为特征。第二代系统使用数字技术，出现于90年代初，通过语音压缩使容量增加三倍左右。第三代系统是对第二代系统的扩展，系统容量扩大到原来第一代系统的10倍以上。0infrastructure基础设施multipath多径multiplex复用inter-symbol码间immunity免疫力channelization信道化orthogonal正交的cellular蜂窝状的videoconferencing电视会议reveal披露，

2、显示connectivity互联性downfall衰败，跌落deployment部署paging寻呼converge收敛，汇集于一点in-building建筑物内的1on-demand按需的teleservice远程服务tolerance允差，宽容度surveillance监视，监督pedestrian行人pico-cell微蜂窝网格tradeoff折衷，妥协undergo经历substantial实质性的hybrid混合的aeronautical航空的maritime航海的terrestrial地面的virtually事

3、实上的rollout展开coverage覆盖2用户稀少降低有线电话高昂基础设施费用的一个方法Thetelecommunicationsindustryfacestheproblemofprovidingtelephoneservicestoruralareas,wherethecustomerbaseissmall,butthecostofinstallingawiredphonenetworkisveryhigh.Onemethodofreducingthehighinfrastructurecostofawiredsy

4、stemistouseafixedwirelessradionetwork.Theproblemwiththisisthatforruralandurbanareas,largecellsizesarerequiredtogetsufficientcoverage.Thispresentsextraproblemsastherearelongdelaytimesinmultipathsignalpropagation.IntroductiontoMobileCommunications3这种技术的码元速率很高，会导致多径引

5、起码间干扰的问题CurrentlyGlobalSystemforMobiletelecommunications(GSM)technologyisbeingappliedtofixedwirelessphonesystemsinruralareasofAustralia.However,GSMusestimedivisionmultiplexaccess(TDMA),whichhasahighsymbolrateleadingtoproblemswithmultipathcausinginter-symbolinterfe

6、rence.4目的是改进蜂窝单元的容量、抗多径干扰以及灵活性各自分别适合于不同的具体应用Severaltechniquesareunderconsiderationforthenextgenerationofdigitalphonesystems,withtheaimofimprovingcellcapacity,multipathimmunity,andflexibility.TheseincludeCDMAandCOFDM.Boththesetechniquescouldbeappliedtoprovideafixed

7、wirelesssystemforruralareas.However,eachtechniquehasdifferentproperties,makingitmoresuitedforspecificapplications.5而对COFDM作为一种移动通信系统的传输方法却研究甚少COFDMiscurrentlybeingusedinseveralnewradiobroadcastsystemsincludingtheproposalforhighdefinitiondigitaltelevision(HDTV)andd

8、igitalaudiobroadcasting(DAB).However,littleresearchhasbeendoneintotheuseofCOFDMasatransmissionmethodformobiletelecommunicationssystems.6基站和移动站都知道用于调制发送数