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1、Chapter1Chapter1IntroductionElementsofaDigitalCommunicationSystem？1-1ElementsofaDigitalCommunication1ElementsofaDigitalCommunicationSystemInformationSourceChannelDigitalSourceEncoderEncoderModulationChannelInformationSourceChannelDigitalSinkDecoderDecoderDemodulation
2、CommunicationChannelsCommunicationChannels？1-2CommunicationChannels--WirelineChannels(Fig1.2-1):Twisted-pairCoaxialcablepair,Coaxialcable,Waveguide,FiberOpticChannels--WirelessChannels:Ground-wave,,ySky-wave,Line-of-sightPropagation--UnderwaterAcousticChannelsUnderwa
3、terAcousticChannels--StorageChannelFig12Fig1.2-2:Frequencyrangeforwireless2:Frequencyrangeforwirelesschannels1-3MathematicalModelsofComm.Channels--Theaddiddiitivenoisechannel:rt()=+αst()nt()(1.3-1)--Thelinearfilterchannelwithadditivenoise:∞r(nóng)t()=+stct()*()nt()=?∫cst()
4、(τττ)d+nt()?∞--ThliThelineartime-varitfiltiantfilterchannel:Theresponseofthechannelattduetoanimpulseappliedattimet-τtotheinputofthechannel,iselapsedtimevariable.τrt()=+st()*(cτ;t)()nt())∞=?∫c()()(τ;ttdt)(stdττ)+n()(tt)((11.33-33))?∞r(nóng)(t)c(τ;t)+S(t)n(t)Multipathchannel
5、Multipathchannel:Lct(;)τδ=?∑atkk()(ττ)(13)(1.34)-4)==k=1rt()=+stct()*(;)(;)τnt()L=?∑atstkk()(τ)+nt()((1.3-5))k=1Wht’thWhat’sthemathmoddlfelofatypicalwirelesstypicalwirelesscommunicationchannel?Multipathandtimevariantchannel!1-4AHistoricalPerspectiveofModernDigitalCiC
6、ommunicatiionForagivenbandwidthandnoISIchannel--Maximumsignalingrate,Nyquist,1924(Equivalenttosamplingtheorem,Shannon,1948)--MaximumdatarateofamultiplelevelsignalMaximumdatarateofamultiplelevelsignaloverabandlimited,channelfixedpowerconstraint(noiseandinterferencecon
7、sidered)(noiseandinterferenceconsidered),Hartley,1928LMSerror,Withnoise--Optimums(t)estimation,Wiener,1942--Channelcapacity(Shannon,1948)PCW=+l(log(11+))/(bitss/(11.44-3)3)2WN0--Coherentanalysisofthevariousdigitalcomm.systembasedonageometricalapproach,Kotelnikov,1947
8、.--Error-detectinganderror-correctingcodes,Hamming,1950.--Advancesintheareaofchannelcoding:*NewBlkBlockcodes:Reed-Solomon(1960);Bos
