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Wideband Code Division Multiple Access



ThesynonymWCDMAgenerallyreferstowidebandcodedivisionmultipleaccess.

Historicalsummary

Inhistory,theEuropeanTelecommunicationsStandardsInstitute(ETSI)begantostudy3GstandardsafterGSM,andthereareseveralalternatives.Itisbasedondirectserialspreadspectrumcodedivisionmultipleaccess,andthethird-generationresearchinJapanalsouseswidebandcodedivisionmultipleaccesstechnology.Afterwards,thetwoareledtomergeanddevelopedintothethirdgenerationinthe3GPPorganization.ThemobilecommunicationsystemUMTSwassubmittedtotheInternationalTelecommunicationUnion(ITU-T).

TheInternationalTelecommunicationUnionfinallyacceptedW-CDMAaspartoftheIMT-20003Gstandard.

IntroductiontoWCDMA

WCDMAmainlyoriginatedfromearlythird-generationwirelessresearchactivitiesinEuropeandJapan.ThegreatsuccessofGSMhasasignificantimpactonthestandardizationofthird-generationsystemsinEurope.EuropelaunchedtheRACEI(ResearchonAdvancedEuropeanCommunicationsTechnology)programin1988andcontinueduntilJune1992.Itrepresentedthebeginningofthethirdgenerationofwirelessresearchactivities.Between1992and1995,EuropestartedtheRACEIIprogram.ACTS(AdvancedCommunicationTechnologyandService)wasestablishedattheendof1995andproposedtheFRAMES(FutureWirelessBroadbandMultipleAccessSystem)solutionforUMTS(UniversalMobileTelecommunicationSystem).Intheseearlystudies,variousaccesstechnologiesincludingTDMA,CDMA,OFDM,etc.wereexperimentedandevaluated.LaidatechnicalfoundationforWCDMA.

Asanemergingtechnology,WCDMAisalsoderivedfromthepracticeandapplicationofCDMAtechnology.WCDMAisrapidlytakingtheworldbystormandhasoccupied80%ofthewirelessmarket.Asof2013,thereweremorethan3.6billionWCDMAusersworldwide,and156operatorsin170countrieshavecommercialized3GWCDMAservices.

WidebandCodeDivisionMultipleAccess,namelyWCDMA.

Abstract:ThisarticlemainlyanalyzesthemaintechnicalcharacteristicsofWCDMA,thedevelopmentstatusandthedirectionoffuturenetworkevolution.ThespecificcharacteristicsandmutualevolutionmethodsofWCDMAtechnologyatdifferentstagesareintroducedrespectively,andthemarketandmainbusinessdirectionsthatWCDMAwillfaceinthefutureareintroduced.ThekeytechnologiesinvolvedintherealizationofWCDMAincluderadiofrequency,intermediatefrequency,basebandRAKEprocessingtechnologyandTurboencodinganddecodingtechnology.Thedifficultiesofdifferenttechnologiesarediscussed.Finally,theprinciplesofenhancedtechnologymulti-userdetectionandsmartantennatechnologyareintroduced.

Keywords:MobileCommunication,WCDMA,RadioAccessNetwork,TheThirdGenerationPartnershipProject

Abstract:Thepaperpresentsthemaintechnologies,currentsituationandevolutionofWCDMA.ThekeyfeaturesandevolutionprocessduringseveralphasesofWCDMAarealsodiscussed.ThefutureservicesandmarketsthatwillbeoccupiedbytheWCDMAsystemareinvolved.Atlastthekeyimplementationissues,handicapsandenhancedtechnologiesinWCDMAreceiverarealsointroduced.

thirdThenextgenerationmobilecommunicationsystem(alsoknownas3G)isthemobilecommunicationmarketthathasexperiencedtheintroductionofthefirstgenerationofanalogtechnologymobilecommunicationservices,andwasintroducedintotheagendaintheboomingdevelopmentofthesecondgenerationofdigitalmobilecommunicationmarket.Intoday'sInternetdatabusinessisconstantlyheatingup,inthecontextofthecontinuousimprovementoffixedaccessrates(HDSL,ADSL,VDSL),thethird-generationmobilecommunicationsystemhasalsoseenthedawnofthemarket,andithasbecomeatelecomoperatorandcommunicationequipmentmanufacturer.Andcommonusersareconcerned.

Mobilecommunicationtechnologybegantodevelopinitsownway.Variouscountriesandtechnicalorganizationsareconstantlydevelopingtheirowntechnologies.TheUnitedStateshasAMPS,D-AMPS,IS-136,IS-95,andJapanhasPHSandPDC.,EuropeisGSM.Thispattern,ontheonehand,mettheneedsofusersintheearlystagesofmobilecommunicationsdevelopmentandopenedupthemobilecommunicationsmarket.Ontheotherhand,italsocausedartificialisolationbetweenregions,triggeringtheneedforaunifiedglobalmobilecommunicationssystem.ItisagainstthisbackgroundthatITUlaunchedthethird-generationmobilecommunicationsystemspecificationworkin1985.

Duringtheconceptevaluationprocessofthethird-generationmobilecommunicationspecificationproposal,widebandcodedivisionmultipleaccess(WCDMA)technologyhasbecomeoneofthemainstream3Gtechnologieswithitsowntechnicaladvantages.HeremainlyintroducestheoriginofWCDMA,themobilecommunicationmarketandbusinessconditionsitfaces,thecharacteristicsofWCDMAtechnology,thecurrentdevelopmentsituationandthedirectionofevolution.

Technicalfeatures

Onlysomekeyfeaturesarelisted

Wirelesscommunicationoccupies5MHzbandwidth

Thebitrateis3.84MChips

Supportedmultiplexingmodes:FDD,TDD

High-speedtransmissiontosupportmultimediaservices

Indoorenvironmentatleast2Mbit/s

Outdoorwalkingenvironmentatleast384Kbit/s

Theoutdoorvehicleenvironmentisatleast144Kbit/s

Misunderstanding

ThenameofW-CDMAisverysimilartoCDMA,andtherelationshipbetweenW-CDMAandCDMAisalsoverysubtle..Botharebasedoncodedivisionmultipleaccesstechnology,andbothusepartofthepatentedtechnologyofQualcomm.ItisgenerallybelievedthattheproposalofW-CDMAwasdevelopedbysomemanufacturersinordertoavoidpatenttraps,andtheirsolutionshaveavoidedQualcommpatentsasmuchaspossible.

Inthefieldofmobilephones,thetermCDMAreferstoseveralrelatedtechnologiesbelongingtothesecondgenerationofmobilephones,includingcodedivisionmultipleaccessspreadspectrummultiplexingtechnology,andQualcommdevelopedincludingcdmaOne(IS-95)andCDMA2000(IS-2000)CDMAstandardfamily.

TheCDMAmultiplexingtechnologyhasexistedforalongtimebeforeQualcommuseditfortheIS-95protocol.However,becausetheCDMAmultiplexingmethodisthemainfeatureoftheIS-95protocolthatdistinguishesitfromotherprotocolssuchasGSM(usingTDMA)atthattime,theprotocolisnowusuallycalledCDMA.

W-CDMAbelongstothethird-generationmobilephonetechnology.ItalsousesCDMAmultiplexingtechnologyanditissimilartotheQualcommstandard.ButW-CDMAisnotjustamultiplexingstandard.Itisacompletespecificationsetthatdefinesindetailhowthemobilephonecommunicateswiththebasestation,howthesignalismodulated,andhowthedataframeisconstructed.

ThetermCDMAinthefieldofmobilecommunicationsusuallyrefersspecificallytotheCDMAstandardfamilydevelopedbyQualcomm.Theydefineasetofmobilecommunicationprotocols.

CDMA,asamultiplexingtechnology,isusednotonlyforW-CDMAairinterfaceprotocol,butalsoforQualcomm'sCDMAprotocol.

W-CDMAspecificallyreferstothemobilephoneprotocoldefinedinIMT-2000.

TheW-CDMAprotocolhasnothingtodowiththeCDMAdevelopedbyQualcomm.

TheCDMAstandardfamily(cdmaOneandCDMA2000)isnotcompatiblewiththeW-CDMAstandardfamily.

Technology

W-CDMAcanuseunpairedorpairedfrequencybands,althoughallcurrentW-CDMAdevices(suchasFOMAandUMTS)usetwo5MHzfrequencybands,oneforuplinkandoneforuplinkUsedfordownstream.

Developmentstatus

MobilecommunicationmarketandWCDMA

Firstofall,theglobalmobilecommunicationisdevelopingveryrapidly.In1999,itexceeded400millionusers,morethanhalfofwhichItisaGSMuser,andtheothersaremainlyPDCandIS-95users.Accordingtothelatestestimates,theglobalmilestoneofreaching1billionuserswillbeinthefirsthalfof2002.ThetimewhenthenumberofInternet-connectedmobilephonesworldwideexceedsthenumberofInternet-connectedPCswillbeadvancedto2002.In2000,themobilephonemarketwithInternetaccessreached60million.Amongthem,mobilephonessupportingWAP(WirelessApplicationProtocol)accountforabout40million.China'smobilecommunicationusershaveexceeded90million.NokiapredictsthatthenumberofInternetmobilephoneswillincreasetoabout200million,including180millionWAPphones.

MobileoperationsmainlyfacetheintroductionofInternetservicesandothervalue-addedservices,suchasbankingservicesandpositioningservices.Inthisregard,Japan’sNTTDoCoMotooktheleadinintroducingtheI-ModemobileInternetserviceandachievedgreatcommercialsuccess.Atpresent,morethan10,000commercialwebsitesareoperatingtheI-Modeservice.Theintroductionofnewservicesputsforwardnewrequirementsonwirelesscommunicationnetworks.GPRS,adatatransmissionschemebasedontheoriginalstandard,isfarfrombeingabletomeetthedemand,andanewbroadbandmobilecommunicationsystemsuitableforbroadbanddataservicesandIPservicesisneeded.

Secondly,theoriginalserviceuseslessspectrum(lessthan100MHz),andthespectrumefficiencyofthesecond-generationtechnologyitselfisrelativelylow,anditcannotevenmeettheneedsofexistingvoice-basedservices..Infact,thereisaseriousshortageofcapacityinthecentralareasofsomecountriesandcities.TheproblemsinJapanandothercountriesandsomecentralcitiesareparticularlyprominent.

TheITUplanned120MHz(1920MHz-1980MHz,2110MHz-2170MHz)symmetricalspectrumresourcesforFDDasearlyasattheWRC92meetingforIMT-2000,and35MHz(1900MHz-1920MHz,2010MHz-2025MHz)non-SymmetricalspectrumresourcesareusedbyTDD.The800MHzfrequencyband(806-960MHz),the1.7GHzfrequencyband(1710-1885MHz),andthe2.5GHzfrequencyband(2500-2690MHz)wereaddedtotheWRC2000meetingforIMT-2000services.Theadditionofthetwomakesthefuture3Gspectrum500MHzAbove,ahugeresourcespaceisreservedforfutureapplications.

Furthermore,theprocessofglobalintegrationurgentlyneedsagloballyunifiedmobilecommunicationsystem.Theexistingmulti-standardairinterfaceandnetworkequipmentofthesecond-generationmobilecommunicationsystemcannotmeetthisrequirement.Therefore,HighhopesareplacedonthenewWCDMA-FDDmobilecommunicationsystem,whichisexpectedtoachieveglobalharmonization.

Finally,mobilecommunicationtechnologyischangingwitheachpassingday.Thestandardizationandindustrializationofthesecond-generationcommunicationsystemhasbeencompletedforalongtime,anditsmainpurposewasonlytosolvetheneedsofvoicecommunicationatthattime.WiththeincreasingmaturityofwirelesscommunicationtechnologiessuchasCDMAandthedevelopmentofwirelessdatacommunicationtechnologies,theoriginalwirelesscommunicationtechnologysystemneedstobeupdatedaccordinglytoimprovetheutilizationefficiencyofspectrumresourcesandincreasethecostandbenefitofoperators.

3Gstandardizationrequirementsaredrivenbybothmarketandtechnology.3Gstandardformulationandsystemdevelopmenthavebeenbasicallycompleted.Thecommercializationof3Gisalsoinprogress.Theearliestcdma2000-1xinSouthKoreastartedcommercializationattheendof2000,andthecommercializationofWCDMA-FDDinJapanisexpectedtobeginaroundJuly2001.ThecommercializationofWCDMAinChinaandEuropeisplannedtobearound2002.

In2001,Japan’sNTTDoCoMo’sFOMAwastheworld’sfirstcommerciallyoperatedW-CDMAservice.J-PhoneJapanPhone(nowSoftwareBank)haslaunchedaW-CDMA-basedservice,claimingthatthe"VodafoneGlobalStandard"iscompatiblewithUMTS(althoughtherewasstillcontroversyin2004).Inearly2003,HutchisonWhampoagraduallyoperatedtheirUMTSnetwork(referredtoas3)globally.

MostEuropeanGSMoperatorsplantolaunchUMTSservicessometimeinthefuture,althoughseveralhaveputthisserviceontheirschedules,andsomehaveevenstartedoperatingUMTSnetworkssincetheendof2003.VodafonewasputintooperationinmultipleUMTSnetworksinEuropeinFebruary2004.VodafonealsoplanstobuildUMTSnetworksinothercountries(includingAustraliaandNewZealand).AT&TWireless(nowacquiredbyCingularandundertheAT&Tbrand)hasopenedUMTSinsomecities.Althoughtheprogressofthenetworkconstructionhasbeendelayedduetothecompany'smerger,CingularhasannouncedplanstodeployW-CDMAwithHSDPAin2005.

Wideband Code Division Multiple Access

TeliaSonerabegantoprovide384kbpsW-CDMAserviceinFinlandonOctober13,2004.Servicesareonlyavailableinmajorcities.ThecommunicationrateisapproximatelyUS$2permegabyte.

Taiwan’s3Gservicebeganinthefourthquarterof2005.InadditiontoAsiaPacificTelecom’suseofCDMA2000,ChunghwaTelecom,Taiwan’sBigBrother,FarEastTelecomandVerbatimTelecomalluseW-CDMAsystems.

ChinaUnicomalsobegantoprovideW-CDMAservicesinmainlandChinaonMay17,2009,andbegantoprovideHSPAservices(andHSPA+servicesinsomeareas).

Marketsituation

3Gmarketdevelopmentrequiresbusinesstraction.Unlikethesecond-generationsystem,itismainlytosolvetheneedsofpeople'svoicecommunicationanytimeandanywhere.3Gcansupportdifferentmediaservices.Capabilities,howtodevelopthesecapabilitiesisanimportantsubjectof3Gbusinessdevelopment.

Inordertoprovidetheabilitytotractionintheearlystageofthemarket,theWCDMAspecificationfocusesonthedevelopmentofbusinesscapabilities.WCDMAisexpectedtoprovideveryrichservices.Youcanenjoyordinary,broadbandvoice,multimediaservices,videophonesandvideoconferencephonesthroughWCDMAterminals;Internetapplicationsonmobilenetworksarealsomorecommon,suchasE-MAIL,WWWbrowsing,e-commerce,electronicgreetingcardsandotherservicesandmobilenetworksCombine.Mobileofficeservicesarealsoadevelopmentdirection:Intranetaccess,enterpriseVPN,etc.willbevigorouslypopularized.Informationandeducationserviceswillhavegoodapplicationprospects,andmobileapplicationssuchasstockinformation,trafficinformation,weatherinformation,locationservices(LCS),onlineclassrooms,andonlinegameswillgreatlyenrichpeople'slives.

IMT-2000proposesnewcharacteristicservicessuchasSoLSAandVHE,makingserviceprovisionmoreflexibleandpersonalized.InR'99,existingtechnologiessuchasMExE,SAT,andCAMELcanbeusedtoembodytheVHEbusinessplatformconcept.WCDMAsupportsmultiplecalls,thatis,itcanprovidetheterminalwiththeabilitytoconductmultipleCScallsorPSsessionsatthesametime.WCDMAprovidesabundanthandovercapabilities(samefrequency,differentfrequencyandhandoverbetweendifferentsystems)toensurebusinesscontinuityissuesinmobilenetworks.

BusinessIP,packetization,multimedia,personalization,andsimplificationofgenerationarethegeneraldevelopmenttrends.Inthefutureservicegenerationsystem,mobilenetworkoperators,serviceproviders(ISP)andcontentproviders(ICP)willworkcloselytogether.Itisparticularlyimportantthatthefuturenetworkwillprovideanopenservicestructure(OSA),andmobileoperatorscandevelopavarietyofflexibleservicesontheopenserviceplatformprovidedbythenetworkbythemselvesorincooperationwithotherorganizations,soastosatisfymobileusers.Higherrequirements.

Comparisonwithotherstandards

Inthebeginning,CDMA2000plannedtousemultiple1.25MHzcarriers,butitwaslaterabandoned,whileW-CDMAusesasingle5MHzbandwidthcarrier.

IntheITUIMT-2000standard,W-CDMAisregardedasCDMAdirectserialspreadspectrum,andCDMA2000iscalled"multi-carrierCDMA".

TheW-CDMAstandardfamily(suchasFOMA,UMTS)isinconsistentwiththeCDMAstandardfamily(suchascdmaOneandCDMA2000).

Evolution

Furtherdevelopment

Inordertomeettheneedsofcommercializationandtechnologicaldevelopment,andtoensuretheinvestmentofnetworkoperators,3GPPhasdividedtheWCDMAstandardintotwomajorTheyare:

Release99(R99)version:SinceDecember1999,itwillbeupdatedeverythreemonths.TheJune2000versionisbasicallystableandreadyfordevelopment.TheversionsinSeptember,DecemberandMarch2001aremorecomplete;themaininterfacesofthewirelessaccessnetworkIu,Iub,andIuralladoptATMandIPmethods.ThenetworkisanATM-basednetwork;thecorenetworkisbasedontheevolvedGSMMSCandGPRSGSN;Thecircuitislogicallyseparatedfromthepacketswitchingnode.

Release2000(R00)version(hasbeenchangedtoRelease4,5...):Mainlyintroduces"all-IPnetwork",initiallyproposedthecorenetworkstructurebasedonIP,didnotstartsubstantialstandardizationwork,therealThe"all-IP"standardisexpectedtobecompletedin2002.Thenetworkstructurewillrealizetheseparationoftransmission,controlandservices.Atthesametime,IPwillgraduallyextendfromthecorenetwork(CN)totheradioaccessnetwork(RAN)andterminal(UE).

ThemainstandardoftheR99versionhasbeencompletedandpublishedin2000.Itcanprovideallthefoundationsfortherealizationofnetworksandterminals,includingallthefunctionalfoundationsoftheuniversalmobilecommunicationnetwork,andprovidethenecessaryguaranteesforthecommercialversion.ThefutureRelease4andRelease5willaddnewfunctionsonthebasisofthesefunctionstoensurethecontinuityofthestandard.FromtheframeworkoftheentireR99network,itcanbeseenthattheinitialWCDMAnetworkcancoexistwiththeGSMnetwork.GSMachievesfullcoverageofawidearea,whileWCDMAachievescoverageofpartofthebusiness-intensiveandhigh-qualitybusinessarea.Thisismainlytoensuretheinvestmentandsmoothtransitionofthesecond-generationoperators.

TheexistingRelease99versionofWCDMAsystemperformanceandservicesaremainly:

Release99versionofWCDMAprovidesanewwirelessaccessnetwork-UTRAN,whichimprovesthespectrumutilizationrate.Highdatatransmissioncapacity,thedatarateis384kbit/sinwidearea,2Mbit/swhenmovingslowlyinasmallrange,supportsAMRvoicecodectechnology,canimprovevoicequalityandsystemcapacity,Iub,IurandIuinterfacesarebasedonATMTechnology,providinganopenIubinterface;

TheWCDMAcorenetworkofRelease99versionisdividedintoCSdomainandPSdomain,whicharebasedontheevolvedMSC/GMSCandSGSN/GGSNrespectively.TheCSdomainismainlyresponsibleforcircuit-typeservicesRelatedfunctionssuchascallcontrolandmobilitymanagement,incallcontrol:useTUP,ISUPandotherstandardISDNsignaling,mobilitymanagementadoptsthefurtherevolvedMAPprotocol,andthephysicalentitysimilartoGSMincludesMSC,GMSC,andVLR.ThePSdomainismainlyresponsibleforfunctionssuchassessioncontrolandmobilitymanagementrelatedtopacket-basedservices.OnthebasisoftheoriginalGPRSsystem,someinterfaceprotocols,workflowsandservicefunctionsarepartiallymodified.Thevoicecodecisimplementedinthecorenetwork.Supportinter-systemhandover(GSM/UMTS),enhancedsecurityperformanceandchargingsystem;

Themainserviceplatformsthatcanbeprovidedinclude:basicpositioningservice,numberportabilityservice,enhancementofintelligentservice,GSMandHandoverbetweenUMTScansupportallGSManditssupplementaryservices,suchascallforwardingwithoutanswer,newUSIMcardprotocol,whichcanimproveuserparticipationandoperation,andsupportbusinessapplicationprogramminginterfaceAPI(openservicestructure),Supportmulticastservices,64kbit/scircuitdatabearerservicesandmultimediaservices;

Systemevolution

Basedontheforegoing,wecansummarizetheevolutionmethodoftheWCDMAsystemasfollows:

-Release99providesathird-generationfull-networksolution.Thestandardhasmatured,andithastheimplementationfoundation,basicfunctionsandexpansionconditionsofcellularmobilenetworks:

–thenewwirelessaccessnetworkUTRAN

p>

–CombinedCSandPSdomaincorenetwork

–EnhancedGSMcorenetworkGERAN

-Release4andRelease5furtherincreasenewservices,optimizetechnicalsystemsandThenetworkstructureisthesupplementandimprovementoftheRelease99protocol,whichensuresthecontinuityoftheWCDMAsystem:

–AllIPnetwork

–Newwirelessaccessmethod-HSDPA

–Enhancedintelligentnetworkandsecurity

Technicalfeatures

Technicalfeatures

1.Basestationsynchronizationmode:supportasynchronousandsynchronousbasestationoperationmode,flexibleNetworking

2.Signalbandwidth:5MHz;Chiprate:3.84Mcps

3.Transmitdiversitymode:TSTD(timeswitchingtransmitdiversity),STTD(time-spacecodingtransmitdiversity),FBTD(FeedbackTransmitDiversity)

4.Channelcoding:ConvolutionalcodeandTurbocode,support2Mratedataservice

5.Modulation:Uplink:BPSK;Downlink:QPSK

6.Powercontrol:uplinkanddownlinkclosed-looppowercontrol,outer-looppowercontrol

7.Demodulationmode:pilot-assistedcoherentdemodulation

8.Voicecoding:AMR,compatiblewithGSM

9.ThecorenetworkisbasedontheevolutionoftheGSM/GPRSnetworkandmaintainscompatibilitywiththeGSM/GPRSnetwork

10.MAPtechnologyAndGPRStunneltechnologyisthecoreofthemobilitymanagementmechanismoftheWCDMAsystem,maintainingcompatibilitywiththeGPRSnetwork

11.SupportSupportsofthandoverandsofterhandover

12.Thebasestationdoesnotneedtobestrictlysynchronized,andthenetworkisconvenient

Advantages

TheadvantageofWCDMA-FDDliesinitshighchiprateEffectiveuseoffrequencyselectivediversityandspatialreceptionandtransmissiondiversity,whichcansolvemultipathandfadingproblems.Turbochannelcodinganddecodingareusedtoprovidehigherdatatransmissionrates.TheFDDformatcanprovidewide-areafullcoverage.Auniquecellsearchmethodisusedforthedifferentiationofdownlinkbasestations,whichdoesnotrequirestrictsynchronizationbetweenbasestations.Usingcontinuouspilottechnology,itcansupporthigh-speedmobileterminals.Comparedwiththesecond-generationmobilecommunicationstandard,WCDMAhas:largersystemcapacity,bettervoicequality,higherspectrumefficiency,fasterdatarate,strongeranti-fadingability,andbetteranti-multipathItcanbeappliedtomobileterminalsupto500km/hintermsoftechnicaladvantages,andcanmakeasmoothtransitionfromtheGSMsystemtoensuretheoperator’sinvestmentandprovideagoodtechnicalfoundationfor3Goperations.

Keytechnology

ThekeytechnologyofWCDMAindustrializationincludesradiofrequencyandbasebandprocessingtechnology,includingradiofrequency,intermediatefrequencydigitalprocessing,RAKEreceiver,channelcodec,powercontrolandotherkeytechnologiesAndmulti-userdetection,smartantennaandotherenhancementtechnologies.

RFandIF

TheRFpartisatraditionalanalogstructure,whichrealizestheconversionofRFandIFsignals.TheRFuplinkchannelpartmainlyincludesautomaticgaincontrol(theRFpartisatraditionalanalogstructure,whichrealizestheconversionofRFandIFsignals.TheRFuplinkchannelpartmainlyincludesautomaticgaincontrol(RFAGC),receivingfilter(Rxfilter)anddownconverterThedownstreamchannelpartofradiofrequencymainlyincludessecondaryup-conversion,broadbandlinearpoweramplifierandradiofrequencytransmissionfilter.Theintermediatefrequencypartmainlyincludesupstreamde-aliasingfilter,down-converter,ADCanddownstreamintermediate-frequencysmoothingfilter,up-converterAndDAC.DifferentfromtheGSMsignalandthefirst-generationsignal,thesignalbandwidthofWCDMAisawidebandsignalupto5MHz.ThelinearityandefficiencyofthewidebandsignalRFpoweramplifierareuniversalcontradictions.

RAKEreceiver

RAKEreceiverisaclassicdiversityreceiverdesignedspecificallyforCDMAsystems.Itstheoreticalbasisis:whenthepropagationdelayexceedsonechipperiod,multipathsignalscanactuallyberegardedasuncorrelated.

ThecorrelatorwithDLLisaphase-lockedloopthatwillsoonerorlater.Itconsistsoftwocorrelators(earlyandlate),andthedemodulationcorrelatorisdifferentfromthedemodulationcorrelatorby±1/2(or1/4)chips.Soonerorlater,thesubtractionofthecorrelationresultofthegatecanbeusedtoadjustthecodephase.Theperformanceofthedelayloopdependsontheloopbandwidth.

ThefunctionofdelayestimationistoobtainthedifferencethroughthematchedfilterSignalenergydistributionatthetimedelayposition,identifythemultipathpositionswithlargerenergy,andallocatetheirtimetothedifferentreceivingpathsoftheRAKEreceiver.Themeasurementaccuracyofthematchedfiltercanreach1/4-1/2chips,andtheintervalbetweendifferentreceivingpathsoftheRAKEreceiverisonechip.Inactualimplementation,iftheupdatespeedofthedelayestimateisveryfast(forexample,onceeverytensofms),thereisnoneedforaphase-lockedloopsoonerorlater./p>

Duetotheinfluenceoffastfadingandnoiseinthechannel,thephaseofeachpathactuallyreceivedvariesgreatlyfromthephaseoftheoriginaltransmittedsignal.Therefore,thephaseshouldberotatedaccordingtotheresultofchannelestimationbeforemerging.ThechannelestimationintheactualCDMAsystemisbasedonthepilotsymbolscarriedinthetransmittedsignal.Accordingtowhetherthetransmittedsignalcarriescontinuouspilots,thephasepredictionbasedoncontinuouspilotsandthephasepredictionbasedondecisionfeedbacktechnologycanbeusedrespectively.Method.

Inthesystem,eachusermustbemultipathsearchedanddemodulated,andthechiprateofWCDMAisveryhigh,andtheprocessingvolumeofitsbasebandhardwareisverylarge.Certainlydifficult.

Channelcodinganddecoding

Channelcodinganddecodingaremainlytoreducethesignalpropagationpowerandsolvetheinevitablefadingproblemofthesignalinthewirelesspropagationenvironment.Thecodinganddecodingtechnologyiscombinedwiththeinterleavingtechnology.Usecanimprovethebiterrorrateperformance.Comparedwiththecaseofnocoding,thetraditionalconvolutionalcodecanincreasethebiterrorratebytwoordersofmagnitudeto10-3~10-4,whiletheTurbocodecanfurtherincreasethebiterrorrateto10-6.ThecandidatechannelcodinganddecodingtechnologiesforWCDMAoriginallyincludedReed-SolomonandTurbocode,Turbocodeisfinallyadoptedas3GdatacodinganddecodingtechnologybecauseitscodinganddecodingperformancecanapproachtheShannonlimit.Convolutionalcodesaremainlyusedforlowdataratevoiceandsignaling.Turbocodingconsistsoftwoormorebasicencoderscascadedinparallelthroughoneormoreinterleavers:

TheprincipleofTurbocodeisbasedonthealgorithmandstructuremodificationoftraditionalconcatenatedcodes.InnerinterleavingTheintroductionofthefiltermakesthepositivefeedbackofiterativedecodingwelleliminated.Turbo'siterativedecodingalgorithmsincludeSOVA(softoutputViterbialgorithm),MAP(maximumposteriorprobabilityalgorithm),etc.SincetheperformanceimprovementofeachiterationoftheMAPalgorithmisbetterthanthatoftheViterbialgorithm,theiterativedecoderoftheMAPalgorithmcanobtaingreatercodinggain.TheactualimplementationoftheMAPalgorithmistheLog-MAPalgorithm,whichplacestheMAPalgorithminthelogarithmicdomainforcalculation,reducingtheamountofcalculation.

ThedifficultyintherealizationofTurbodecodingalgorithmliesinthedecodingrateandcorrespondingnumberofiterationsforhigh-speeddata.ExistingDSPshavebuilt-inbasicalgorithmsrequiredbydecoders,sothatTurbodecodingcanbedirectlyrealizedbyrelyingonDSPchips.WithoutusingASIC.

Implementationdifficulties

Smartantennatechnologyusesadaptivebeamformingtechnologytoincreasethedirectionalpatterngainoftheuser'sdirectionofarrival,andatthesametimeusethezeropointofthedirectionalpatterntoreducespatialhighpowerUserinterference.Themaindifficultyliesintheinconsistencyandcorrectiontechnologyofmulti-channel,thehighcomplexityofRAKEreceivercombinedwithbasebandprocessing,andtheinconsistencyoftheuplinkanddownlinkdirectionsofarrivalcausedbyFDDtechnology.

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