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1、Chapter6BandwidthUtilization:MultiplexingandSpreadingCopyright©TheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.1Bandwidthutilizationisthewiseuseof availablebandwidthtoachieve specificgoals.Efficiencycanbeachievedbymultiplexing;privacyandanti-jammingcan
2、beachievedbyspreading.Note26-1MULTIPLEXINGWheneverthebandwidthofamediumlinkingtwodevicesisgreaterthanthebandwidthneedsofthedevices,thelinkcanbeshared.Multiplexingisthesetoftechniquesthatallowsthesimultaneoustransmissionofmultiplesignalsacrossasingledatalink.Asdataandtelecomm
3、unicationsuseincreases,sodoestraffic.Frequency-DivisionMultiplexingWavelength-DivisionMultiplexing SynchronousTime-DivisionMultiplexingStatisticalTime-DivisionMultiplexingTopicsdiscussedinthissection:3Figure6.1Dividingalinkintochannels4Figure6.2Categoriesofmultiplexing5Figur
4、e6.3Frequency-divisionmultiplexing6FDMisananalogmultiplexingtechniquethatcombinesanalogsignals.Note7Figure6.4FDMprocess8Figure6.5FDMdemultiplexingexample9Assumethatavoicechanneloccupiesabandwidthof4kHz.Weneedtocombinethreevoicechannelsintoalinkwithabandwidthof12kHz,from20to3
5、2kHz.Showtheconfiguration,usingthefrequencydomain.Assumetherearenoguardbands.SolutionWeshift(modulate)eachofthethreevoicechannelstoadifferentbandwidth,asshowninFigure6.6.Weusethe20-to24-kHzbandwidthforthefirstchannel,the24-to28-kHzbandwidthforthesecondchannel,andthe28-to32-k
6、Hzbandwidthforthethirdone.ThenwecombinethemasshowninFigure6.6.Example6.110Figure6.6Example6.111Fivechannels,eachwitha100-kHzbandwidth,aretobemultiplexedtogether.Whatistheminimumbandwidthofthelinkifthereisaneedforaguardbandof10kHzbetweenthechannelstopreventinterference?Soluti
7、onForfivechannels,weneedatleastfourguardbands.Thismeansthattherequiredbandwidthisatleast5×100+4×10=540kHz,asshowninFigure6.7.Example6.212Figure6.7Example6.213Fourdatachannels(digital),eachtransmittingat1Mbps,useasatellitechannelof1MHz.Designanappropriateconfiguration,usingFD
8、M.SolutionThesatellitechannelisanalog.Wedivideitintofourchannels,eachchanne
