通信系统绪论课件

CommunicationSystems

（FourthEdition）

SimonHaykin

1

CommunicationSystems

Contents

CH0:BackgroundandPreviewCH1:RandomProcessesCH2:Continuous-WaveModulationCH3:PulseModulationCH4:BasebandPulseTransmissionCH5:Signal-SpaceAnalysisCH6:PassbandDataTransmissionCH7:Spread-SpectrumModulationCH8:MultiuserRadioCommunicationsCH9:FundamentalLimitsinInformationTheoryCH10:Error-ControlCoding2ContentsCH0:BackgroundandPCh.0BackgroundandPreviewTheCommunicationProcessPrimaryCommunicationResourcesSourcesofInformationCommunicationNetworksCommunicationChannelsModulationProcessAnalogandDigitalTypesofCommunicationShannon’sInformationCapacityTheoremADigitalCommunicationsProblemHistoricalNotes3Ch.0BackgroundandPreviewThe0.1TheCommunicationProcessFig.1.Elementsofacommunicationsystem.40.1TheCommunicationProcessFTheCommunicationProcess(cont’d)ThreebasicelementstoeverycommunicationsystemTransmitter:toconvertthemessagesignalproducedbythesourceofinformationintoaformsuitablefortransmissionoverthechannelChannel:introducesdistortionandnoiseReceiver:toreconstructtheoriginalmessagesignalfromthereceivedsignal5TheCommunicationProcess(conTheCommunicationProcess(cont’d)TwobasicmodesofcommunicationBroadcastingOne-to-manycommunicationUsuallyonedirectionalflowofsignalsE.g.radioandtelevisionPoint-to-pointcommunicationOne-to-onecommunicationUsuallybidirectionalflowofsignalsE.g.telephoneandsatellitecommunicationOnecommonfeatureofcommunicationprocess:Statisticalinnature6TheCommunicationProcess(con0.2PrimaryCommunicationResourcesTransmittedpower:theaveragepowerofthetransmittedsignalChannelbandwidth:thebandoffrequenciesallocatedforthetransmissionofthemessagesignalTwotypesofcommunicationchannels:Powerlimited:e.g.satellitechannelBandlimited:e.g.telephonecircuitNoiseUnwantedandunavoidableThesignal-to-noiseratio(SNR)Usuallyexpressedindecibels(dBs),SNRdB=10log10(SNR)70.2PrimaryCommunicationReso0.3SourcesofInformationFourimportantsourcesofinformation:Speech:Usingthe300–3100HzbandMusic:upto15kHzPicturesCanbedynamic(e.g.television)orstatic(e.g.facsimile)ThescanningprocessWidebandsignalsComputerdataTheAmericanStandardCodeforInformationInterchange(ASCII)WidebandsignalsBurstinessCompression(losslessandlossy)80.3SourcesofInformationFour0.4CommunicationNetworksFig.4.Communicationnetwork.90.4CommunicationNetworksFig.CommunicationNetworks–SwitchingModeCircuitswitchingE.g.thetelephonenetworkSuitabletorelativelystableandlongdurationsignals,suchasvoicePacketswitchingE.g.theInternet“Storeandforward”SuitabletocomputercommunicationwheredataisburstyinnatureRequirescarefulcontrolfromendusers10CommunicationNetworks–SwitcCommunicationNetworks–LayeredArchitectureFig.5.OSImodel.11CommunicationNetworks–LayerCommunicationNetworks–InternetFig.6.Aninterconnectednetworkofsubnets.NetworkofnetworksUnderlyingnetworktechnologyisdecoupledfromtheapplicationsBesteffortservice12CommunicationNetworks–InterCommunicationNetworks–Internet(Cont’d)Fig.7.IllustratingthenetworkarchitectureoftheInternet.13CommunicationNetworks–InterCommunicationNetworks–BroadbandNetworksB-ISDNStandsfor“broadbandintegratedservicesdigitalnetworks”EvolvesfromtelephonenetworkwhosemajorserviceisvoiceSupportsmultimediacommunicationsTheunderlyingtechnologyisasynchronoustransfermode(ATM)14CommunicationNetworks–BroadATMAcell-switchingtechnologyBasictransmissionunitiscells(small,fixed-sizepackets)PreservescellsequencingintransmissionIsnotsynchronousHighbandwidthandlowdelayProvidequalityofservice(QoS)guaranteesQoSismeasuredintermsoflossratio,delay,anddelayvariationCommunicationNetworks–BroadbandNetworks(Cont’d)15ATMCommunicationNetworks–BrSONETStandsfor“synchronousopticalnetwork”Usingtime-divisionmultiplexing(TDM)NeedsynchronizationAhierarchyofdataratesThebasicrateis51.84Mb/sByte-interleavedtogeneratehigherratesCommunicationNetworks–BroadbandNetworks(Cont’d)16SONETCommunicationNetworks–0.5CommunicationChannelsGuidedpropagationTelephonechannelsCoaxialcablesOpticalfibersFreepropagationBroadcastchannelsMobileradiochannelsSatellitechannelsDifferentwaysofclassificationLinearornonlinearTimeinvariantortimevaryingBandlimitedorpowerlimited170.5CommunicationChannelsGuidCommunicationChannels–TelephoneChannelsBandwidthlimited(300–3100Hz)UsingtwistedpairsSusceptibletoelectromagneticinterference(EMI)Fig.8.Characteristicsoftypicaltelephoneconnection:(a)Insertionloss.(b)Envelopedelay.(AdaptedfromBellamy,1991.)18CommunicationChannels–TelepCommunicationChannels–CoaxialCablesBetterimmunitytoEMIthantwistedpairsHasacharacteristicimpedanceof50or75ohmsHigherbandwidththantwistedpairs(upto20Mb/s)Canbeusedasamultiple-accessmediumApplicationsLocalareanetworks(LAN)Cable-televisionsystems19CommunicationChannels–CoaxiCommunicationChannels–OpticalFibersDielectricwaveguidetransportinglightsignalsEnormouspotentialbandwidth(21013Hz)Lowtransmissionlosses(0.1dB/km)ImmunitytoEMI(dielectric)Smallsizeandweight(thinnerthanahair)RuggednessandflexibilityLowcostofthematerials20CommunicationChannels–OpticCommunicationChannels–WirelessBroadcastChannelsInformation-bearingsignalisusuallymodulatedfortransmissionAntennaisusedtoefficientlytransmitandreceiveelectromagneticwavesTypicallyline-of-sight(LOS)propagationThesuper-heterodynetypereceiver21CommunicationChannels–WirelCommunicationChannels–MobileRadioChannelsTypicallynon-line-of-sight(NLOS)propagationThemultipathphenomenonTheenergyreachesthereceivingantennaviamorethanonepathResultingfromscatteringofsignalsduringpropagationLinearandtime-varying22CommunicationChannels–MobilCommunicationChannels–SatelliteChannelsCommunicatingthroughgeostationarysatellitesBroad-areacoverageReliabletransmissionlinksWidetransmissionbandwidth(6GHzfortheuplinkand4GHzforthedownlink)23CommunicationChannels–Satel0.6ModulationProcessThemodulationprocessvariessomeparameterofacarrierwaveinaccordancewiththemessagesignal,sothattheresultingsignalissuitablefortransmissionoverthechannel.Demodulationisthereverseofmodulation.240.6ModulationProcessThemoduModulationProcess–ClassificationContinuous-wavemodulationThecarrierisasinusoidalwaveAmplitudemodulation(AM)AnglemodulationFrequencymodulation(FM)Phasemodulation(PM))PulsemodulationThecarriesisaperiodicsequenceofpulsesAnalogpulsemodulation(PAM,PDM,andPPM)Digitalpulsemodulation(PCM)25ModulationProcess–ClassificModulationProcess–MultiplexingMultiplexingistheprocessofcombiningseveralmessagesignalsfortheirsimultaneoustransmissionoverthesamechannel.Frequency-divisionmultiplexing(FDM)Time-divisionmultiplexing(TDM)Code-divisionmultiplexing(CDM)Wavelength-divisionmultiplexing(WDM)(aformofFDM)26ModulationProcess–Multiplex0.7AnalogandDigitalTypesofCommunicationFig.9.Blockdiagramofdigitalcommunicationsystem.270.7AnalogandDigitalTypesoAnalogDigitalTypesofCommunication–DigitalCommunicationSystemiscomplex,includingSourceencoder-decoderChannelencoder-decoderModulator-demodulatorEasytobuildEfficientandreliableWiththeever-increasingavailabilityofvery-large-scaleintegrated(VLSI)circuits,digitalcommunicationsbecomepopulartoday.28AnalogDigitalTypesofCommunAnalogDigitalTypesofCommunication–AnalogCommunicationSystemissimpleDifficulttobuildStringentrequirementsonlinearityDifficultonsystemadjustmentVeryhigh-speedandverylow-powercommunicationsystemsmaydictatetheuseofananalogapproach.29AnalogDigitalTypesofCommun0.8Shannon’sInformationCapacityTheoryBiterrorrate(BER)–reliabilitymetricTheinformationcapacitytheoryAmessagesignalcanbetransmittedthroughthesystemwithouterrorprovidedthattheactualsignalingrateislessthantheinformationcapacityC,C=Blog2(1+SNR)b/swhereBisthechannelbandwidth.300.8Shannon’sInformationCap