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.
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.