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DVB-C系统的复用技术
Introduction
DVB-C,orDigitalVideoBroadcasting-Cable,isastandarddevelopedbytheDigitalVideoBroadcasting(DVB)project,whichisaninternationalconsortiumofbroadcasters,manufacturers,andregulatorybodies.DVB-CisusedfordigitalcableTVtransmissionandreceptionusingcablenetworks.Thesystemusesarangeoftechnologiesformultiplexing,includingtimedivisionmultiplexing(TDM),frequencydivisionmultiplexing(FDM),andcodedivisionmultiplexing(CDM).Inthispaper,IwilldiscussthemultiplexingtechnologiesusedinDVB-Candhowtheyareusedtotransmitmultiplechannelsoverasinglecablenetwork.
TimeDivisionMultiplexing(TDM)
TimedivisionmultiplexingisawidelyusedtechniqueintelecommunicationsandisalsousedinDVB-C.InTDM,multiplechannelsaretransmittedoverasinglechannel,witheachchannelallottedaspecifictimeslotwithinthechannel.Eachtimeslotcarriesdataforaspecificchannelandthechannelsareseparatedbyguardtimestopreventcrosstalk.ThistechniqueisusedinDVB-Cforvideo,audio,anddatatransmission.Thedatastreamforeachchannelisdividedintopacketsandthesepacketsaretransmittedoverthechannelinaround-robinfashion.Thereceiverthenusesademultiplexertoextractthedatapacketsforthedesiredchannel.
FrequencyDivisionMultiplexing(FDM)
FrequencydivisionmultiplexingisanotherwidelyusedtechniqueintelecommunicationsandisalsousedinDVB-C.InFDM,multiplechannelsaretransmittedoverasinglechannelbydividingtheavailablebandwidthintomultiplefrequencybands,witheachbandallottedtoaspecificchannel.Thechannelsareseparatedbyguardbandstopreventinterference.Acarrierfrequencyisusedtomodulatethedataforeachchannelandthemodulatedsignalsarethencombinedtoformacompositesignalfortransmission.ThistechniqueisusedinDVB-CfordigitalTVtransmission.
CodeDivisionMultiplexing(CDM)
CodedivisionmultiplexingisanewertechniquethatisusedinsomewirelesscommunicationsystemsandisalsousedinDVB-C.InCDM,multiplechannelsaretransmittedoverasinglechannelusingauniquecodeforeachchannel.Eachchannelismodulatedwithauniquecodethatisorthogonaltothecodesusedforotherchannels.Thisallowsmultiplechannelstob