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CDMA无线网络关键技术研究
CDMA(CodeDivisionMultipleAccess)technologyhasbeenwidelyusedinwirelessnetworkingandcommunication.Itisaspreadspectrumtechniquethatusesuniquecodestoseparateanddistinguishindividualusersignalsinasharedfrequencyband.Thistechnologyenablesmultipleuserstousethesamefrequencybandsimultaneously,providinghighcapacityandqualityforwirelesscommunication.
Inthispaper,wewilldiscussthekeytechnologiesrelatedtoCDMAwirelessnetworksandtheirresearchdevelopments.WebelievethatunderstandingthesetechnologiesisessentialforoptimizingtheperformanceandefficiencyofCDMAwirelessnetworks.
CDMANetworkArchitecture
ThearchitectureofaCDMAnetworkconsistsofdifferentcomponentssuchasthebasestation,mobilestation,andnetworkinfrastructure.Thebasestationservesasthecommunicationhubandprovideswirelesscoverageinaparticulararea.Themobilestationoruserdevicecommunicateswiththebasestationtoestablishandmaintainthecommunicationlink.Thenetworkinfrastructureincludesthecorenetworkandbackhaulnetwork,whereallthecontrolandmanagementfunctionsarecarriedout.
SignalSpreadingTechniques
CDMAusesauniquespreadingcodetodistinguishbetweenmultipleusers.Thespreadingcodeismultipliedwiththeuser'sinformationbitstomakethesignalspreadacrossabroadfrequencyrange.Therearetwotypesofspreadingtechniques,directsequence(DS)spreadingandfrequencyhopping(FH)spreading.
InDS,apseudo-randomcodeisgeneratedatahigherfrequencythanthedatarateandismultipliedwiththeuser'sdatatogeneratethespreadspectrumsignal.Thistechniqueallowsmultipleuserstosharethesamefrequencyband,asthesignalsaredistinguishedbytheuniquespreadingcodes.
InFH,thesignalistransmittedusingmultiplecarrierfrequenciesthatchangerapidlyinaknownsequence.Thesignalisthenre-constructedatthereceiverendbyfollowingthesamecarrierfrequencysequence.FHhelpsachievefrequencydiversityandprovidesrobusttransmissionagainstinterferenceandfading.
PowerControl
PowercontrolisacrucialtechniqueusedinCDMAnetworkstooptimizethetransmitpoweroftheuser'ssignal.Theobjectiveistokeepthetransmitpoweraslowaspossibletominimi