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Time division multiplexing



Basicprinciple

Schematicdiagramofn-channeltime-divisionmultiplexingsystem:

Schematicdiagramofn-channeltime-divisionmultiplexingsystem(1picture)

Timedivisionmultiplexingissuitableforthetransmissionofdigitalsignals.Becausethebittransmissionrateofthechannelexceedsthedatatransmissionrateofeachsignal,thechannelcanbedividedintoseveralsegmentsaccordingtotimeandusedformultiplesignalsinturn.Eachtimesliceisseparatelyoccupiedbyamultiplexedsignal.Inaspecifiedtime,multipledigitalsignalscanbetransmittedandarrivedasrequired,whichalsorealizesthetransmissionofmultipledigitalsignalsonaphysicalchannel.Assumingthatthebitrateofeachinputdatais9.6kbit/sandthemaximumbitrateofthelineis76.8kbit/s,8signalscanbetransmitted.Atthereceivingend,asophisticateddecodercanaccuratelydistinguishdifferentdigitalsignalsbyreceivingsomeadditionalinformation.

Features

Timedivisionmultiplexingisbasedonthesamplingtheorem.Thesamplingtheoremmakesitpossibleforcontinuous(analog)basebandsignalstobereplacedbysamplingpulsevalues​​thatappeardiscretelyintime.Inthisway,whenthesamplingpulseoccupiesashorttime,atimegapisleftbetweenthesamplingpulses,andthesamplingvalueofothersignalscanbetransmittedbyusingthisgap.Therefore,itispossibletotransmitseveralbasebandsignalssimultaneouslyalongachannel.

Timedivisionmultiplexingtechnology

Time-pisionmultiplexingtechnology(time-pisionmultiplexing,TDM)istointerweavedifferentsignalsindifferenttimeperiodsandtransmitthemalongthesamechannel;Atthereceivingend,useacertainmethodtoextractthesignalineachtimeperiodandrestoreittothecommunicationtechnologyoftheoriginalsignal.Thistechnologycantransmitmultiplesignalsonthesamechannel.

Applicationextension

TheTDMmethodisdividedintothefollowingtwotypes

Synchronoustimedivisionmultiplexingsystem(twotypes):

1,PlesiochronousseriesPDH(usedinpublictelephonenetworkPSTN).

2.SynchronousSDHseries(usedinbackbonenetworkssuchasopticalfibercommunication)

Statistics(asynchronous)timedivisionmultiplexingsystem(twotypes):

1,Virtualcircuitmode(suchasX.25,framerelay,ATM).

2.Datagrammethod(suchasTCP/IP)

PSTNsystemadoptsacombinationofPDHandSDH,andPCM/PDHisusedforaccessandexchangeofsmallusers,andthecorebackbonenetworkUseSDH.

TherearetwotypesofPDHstandardsintheworld

1.A30/32-channelPCMsystembasedonA-lawcompression(Europeanstandards,usedinEurope,China,Russia,etc.)

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2,24-channelPCMsystembasedonu-lawcompression(Americanstandard,usedinNorthAmerica,Japan,Taiwan,etc.)

Timeslicedivision:

Synchronous)TimedivisionmultiplexingTDM,itstimesliceispre-allocated,anditisfixed,sothetransmissiontimingofvarioussignalsourcesissynchronized.Incontrast,asynchronoustimedivisionmultiplexing1DMallowsforthedynamicallocationoftimeslicesofthetransmissionmedium.

Development:

Althoughthetraditionalcircuittime-divisionmultiplexingtechnologyhasmatured,itisdifficulttofurtherincreasethetransmissionrateofasingleopticalfiberduetotheinfluenceoftheelectronicbottleneck.Thetransmissionrateofasingleopticalfibercanbe10Gbit/sbyusingelectricaltimedivisionmultiplexing.AlthoughtheGermanSHF40Gbit/selectricaltimedivisionmultiplexerhasbeencommercialized,itisveryexpensiveduetoitscomplextechnology.Therefore,inordertofurtherimprovethecommunicationcapacityoftheopticalcommunicationsystem,peoplefocusontheresearchfocusonthetwomultiplexingmodesofopticalwavelengthdivisionmultiplexing(WDM)andopticaltimedivisionmultiplexing(OTDM).

WDMistomultiplexmultipleopticalsignalsofdifferentwavelengthsonanopticalfiber,anddemultiplexthedifferentwavelengthsatthereceivingend.Duetothedevelopmentofgain-flatteningEDFA,whichhaspromotedthedevelopmentofWDMtechnology,WDMhasbecomeincreasinglymature.OTDMonlytransmitsopticalsignalsofonewavelengthonanopticalfiber.ItfirstrequiresthattheopticalpulsesmustbeRZcodes.Eachopticalsignalismultiplexedintoonechannelbyoccupyingdifferenttimeslots.Thefirstopticalpulsewithdifferenttimedelaysisusedtoincreasethetransmissionrateofasingleopticalfiber.WDMandOTDMeachhavetheirownadvantages,soitcanbeforeseenthatthecombinationofWDMandOTDMwillgreatlyincreasethecapacityofopticalcommunicationsandbecomeatrendinthedevelopmentofopticalcommunicationsinthefuture.

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