08-复用

通信工程学院主讲教师：祁永敏Chapter8Multiplexing复用PRESENTEDBYYONGMINQI(祁永敏)主讲教师：祁永敏通信工程学院Overview8.1FrequencyDivisionMultiplexing（FDM）8.2SynchronousTimeDivisionMultiplexing（TDM）8.3StatisticalTDM8.4AsymmetricalDigitalSubscriberLine（ADSL）非对称数字用户线路主讲教师：祁永敏通信工程学院Multiplexing高效——多个信道共享数据链路的容量主讲教师：祁永敏通信工程学院8.1FDMEachsignalismodulatedtoadifferentcarrierfrequencyCarrierfrequenciesseparatedsosignalsdonotoverlape.g.broadcastradioFDM多路信号被调制到不同的频率上。FDMSystem复合基带信号的频谱副载波调制器带通滤波器三个话音频带信号的频分复用话音信号的频谱调制到64kHz频率上的话音信号的频谱下边带上边带主讲教师：祁永敏通信工程学院AnalogCarrierSystemsAT&T(USA)：HierarchyofFDMschemesGroup基群12voicechannels(4kHzeach)=48kHzRange60kHzto108kHzSupergroup超群60channelFDMof5groupsignalsoncarriersbetween420kHzand612kHzMastergroup主群10supergroups主讲教师：祁永敏通信工程学院WavelengthDivisionMultiplexing(WDM)波分复用MultiplebeamsoflightatdifferentfrequencyCarriedbyopticalfiberAformofFDMEachcoloroflight(wavelength)carriesseparatedatachannel主讲教师：祁永敏通信工程学院WDM波分复用1997BellLabs100beamsEachat10GbpsGiving1terabitpersecond(Tbps)Commercialsystemsof160channelsof10GbpsnowavailableLabsystems(Alcatel)256channelsat39.8Gbpseach10.1TbpsOver100km主讲教师：祁永敏通信工程学院WDMOperationNumberofsourcesgeneratinglaserbeamsatdifferentfrequenciesTransmissionoversinglefiberOpticalamplifiersamplifyallwavelengthsTypicallytensofkmapartDemuxseparateschannelsatthedestinationMostly1550nmwavelengthrangeWas200GHzperchannel，now50GHz光发射机…光发射机光接收机光接收机…1n1n1…n1n光接收机…光接收机复用/解复用器光纤放大器光发射机光发射机…1′n′n＋1…2n1′n′复用/解复用器n＋12n单纤双向WDM传输系统主讲教师：祁永敏通信工程学院DenseWDM（DWDM）密集波分复用NoofficialorstandarddefinitionImpliesmorechannelsmorecloselyspacedthanordinaryWDM50GHzorless主讲教师：祁永敏通信工程学院8.2SynchronousTimeDivisionMultiplexing同步时分复用DatarateofmediumexceedsdatarateofdigitalsignaltobetransmittedMultipledigitalsignalsinterleaved交错传输intimeTimeslots时隙preassignedtosourcesandfixedTimeslotsallocatedevenifnodataTimeslotsdonothavetobeevenlydistributedamongstsourcesTDMTDMSystem扫描操作时隙：可能是空的，也可能被占用主讲教师：祁永敏通信工程学院TDMLinkControlNoheadersandtrailersDatalinkcontrolprotocolsnotneededFlowcontrolDatarateofmultiplexedlineisfixedIfonechannelreceivercannotreceivedata,theothersmustcarryonThecorrespondingsourcemustbequenched中止ThisleavesemptyslotsErrorcontrolErrorsaredetectedandhandledbyindividualchannelsystems基于单信道的差错控制DataLinkControlonTDM主讲教师：祁永敏通信工程学院PulseStuffing脉冲填充Problem-SynchronizingdatasourcesClocksindifferentsourcesdriftingSolution-PulseStuffingOutgoingdataratehigherthansumofincomingratesStuffextradummy空bitsorpulsesintoeachincomingsignaluntilitmatcheslocalclock模拟和数字源的时分复用模拟源数字源通过填充将每个源的速率提高到8kbps主讲教师：祁永敏通信工程学院DigitalCarrierSystems数字载波系统HierarchyofTDMUSA/Canada/JapanuseonesystemITU-Tuseasimilar(butdifferent)systemUSsystembasedonDS-1formatMultiplexes24channelsEachframehas8bitsperchannelplusoneframingbit193bitsperframe主讲教师：祁永敏通信工程学院DigitalCarrierSystems(2)Forvoiceeachchannelcontainsonewordofdigitizeddata(PCM,8000samplespersec)Datarate8000x193=1.544Mbps主讲教师：祁永敏通信工程学院MixedDataDS-1cancarrymixedvoiceanddatasignals24channelsusedNosyncbyteCanalsointerleaveDS-1channelsDs-2isfourDS-1giving6.312MbpsDS-1TransmissionFormat帧定位主讲教师：祁永敏通信工程学院SONET/SDH(同步光网络/同步数字系列)SynchronousOpticalNetwork(ANSI)SynchronousDigitalHierarchy(ITU-T)SignalHierarchySynchronousTransportSignallevel1(STS-1)一级同步传送信号orOpticalCarrierlevel1(OC-1)51.84MbpsCarryDS-3orgroupoflowerratesignals(DS1DS1CDS2)plusITU-Trates(e.g.2.048Mbps)MultipleSTS-1combinedintoSTS-NsignalITU-Tlowestrateis155.52Mbps(STM-1)SONETFrameFormat段开销线路开销通道开销SONETSTS-1OverheadOctets主讲教师：祁永敏通信工程学院StatisticalTDMInSynchronousTDMmanyslotsarewastedStatisticalTDMallocatestimeslotsdynamicallybasedondemand按需分配MultiplexerscansinputlinesandcollectsdatauntilframefullDatarateonlinelowerthanaggregateratesofinputlines不会出现所有连接设备在任何时间都在传输的情况。StatisticalTDMFrameFormats一般的帧子帧多个源点的子帧主讲教师：祁永敏通信工程学院CableModemOutlineTwochannelsfromcableTVproviderdedicatedtodatatransferOneineachdirectionEachchannelsharedbynumberofsubscribersSchemeneededtoallocatecapacityStatisticalTDM主讲教师：祁永敏通信工程学院8.4AsymmetricalDigitalSubscriberLine非对称数字用户线路ADSL：使用FDM充分利用双绞线的1MHz容量LinkbetweensubscriberandnetworkUsescurrentlyinstalledtwistedpaircableCancarrybroaderspectrum主讲教师：祁永敏通信工程学院ADSLDesignAsymmetricGreatercapacitydownstreamthanupstreamFDMLowest25kHzforvoice——Plainoldtelephoneservice(POTS)传统电话业务Useechocancellation回声抵消orFDMtogivetwobands(上行频带、下行频带)UseFDMwithinbandsRange5.5kmADSLChannelConfiguration可变上行链路的整个频带与下行链路的低频区重合主讲教师：祁永敏通信工程学院DiscreteMultitone离散多音调制DMTMultiplecarriersignalsatdifferentfrequencies4kHzsubchannelsSendtestsignalandusesubchannelswithbettersignaltonoiseratio256downstreamsubchannelsat4kHz15.36MHzrate(每个4kHz的子信道承载60kbps)Impairments损伤bringthisdownto1.5Mbpsto9MbpsDTMBitsPerChannelAllocation在不同的频率使用多个载波信号主讲教师：祁永敏通信工程学院xDSLHighdatarateDSL高数据率数字用户线路SinglelineDSL单线数字用户线路VeryhighdatarateDSL甚高数据率数字用户线路主讲教师：祁永敏通信工程学院HomeworkWhatisFDM?WhatisTDM?WhatisSTDM?