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MultipleaccesstechnologyMobileCommunicationTechnologyLecturer：XXXXX0102SummaryCommonmultipleaccesstechnologyCONTENT01SummaryPARTONESummaryMultiplemobileusersneedtocommunicatewithothermobileusersthroughabasestationatthesametime.Differentcharacteristicsmustbegiventothesignalssentbybasestationsanddifferentmobileusers.Thebasestationcandistinguishwhichmobileusersendsthesignalfromthesignalsofmanymobileusers.Atthesametime,eachmobileusercanidentifywhichofthesignalssentbythebasestationissenttoitself.02CommonmultipleaccesstechnologyPARTTWOCommonmultipleaccesstechnology频率时间功率TDMAFDMA频率时间功率CDMA时间频率功率Code1Code2CodeNFDMA：FrequencyDivisionMultipleAccess

TDMA：TimeDivisionMultipleAccessCDMA：CodeDivisionMultipleAccessQuestion:accordingtothesharingmodeofchannelresources,whatchannelresourcesarethere?CommonmultipleaccesstechnologyFDMAPrincipleIfthechannelisdistinguishedbyfrequency,thetotalfrequencybandofthecommunicationsystemisdividedintoseveralequalintervalchannelsandallocatedtodifferentusers.Eachmobileuserisassignedanaddress,thatis,inaradiofrequencyband,eachmobileuserisassignedachannel,andthesechannelsdonotoverlapeachotherinthefrequencydomain.ThefigurebelowshowsthefdmasystemcomposedofoneBSandKMs.CommonmultipleaccesstechnologyChanneldivisionofFDMATransceiverintervalInordertoavoidinterferencebetweentransmitterandreceiverofthesameradiostation,thefrequencyinterval|f-f|mustbegreaterthanacertainvalue.Forexample,inthe800MHzfrequencyband,theintervalbetweentransmitandreceivefrequenciesisusually45MHz.CommonmultipleaccesstechnologyCharacteristicsofFDMA1.Eachchanneltransmitsonlyonesignal.Aslongasthechannelisassignedtothemobilestation,signalswillbecontinuouslyreceivedandtransmittedbetweenthemobilestationandthebasestation.2.Becausethetransmitterandreceiverworkatthesametime,inordertoseparatethetransmitterandreceiver,theduplexermustbeused.3.FDMAadoptssinglecarrierandsinglechannelmode.Ifabasestationhas30channels,eachbasestationneeds30setsoftransceiverequipment,whichcannotbeshared,thatis,thecostofpublicequipmentishigh.CommonmultipleaccesstechnologyApplicationofFDMA

ThefirstgenerationanalogmobilecommunicationsystemNorthAmerica:AMPSTACssysteminEuropeandChina:TACSCommonmultipleaccesstechnologyTDMAPrincipleIfthechannelisdividedbytimeslot,thetimeisdividedintoperiodicframes,andeachframeisfurtherdividedintoseveraltimeslots(frameandtimeslotarenotoverlapped),andthenaccordingtocertainallocationprinciple,eachmobilestationcanonlysendsignalstothebasestationinthespecifiedtimeslotineachframe.Eachmobileuserisassignedanaddress,thatis,eachmobileuserisassignedatimeslotinatimeperiod(timeframe).MS1occupiestimeslot1，MS2occupiestimeslot2，MSkoccupiestimeslotk.Commonmultipleaccesstechnology

Framestructureoffrequencydivisionforward/backwardchannelCommonmultipleaccesstechnology

Framestructureoftimedivisionforward/backwardchannelCommonmultipleaccesstechnologyCharacteristicsofTDMA(1)ThebasestationofTDMAsystemcanuseonlyonetransmitter;(2)TDMAsystemmusthaveaccuratetimingandsynchronizationtoensurethatthesignalssentbyeachmobilestationwillnotoverlapormixupinthebasestation,andcanreceivethesignalsfromthebasestationaccuratelyinthespecifiedtimeslot.SynchronizationtechnologyisanimportantguaranteeforTDMAsystemtoworknormally.

CommonmultipleaccesstechnologyApplicationofTDMASecondgenerationdigitalmobilecommunicationsystem

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