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, jmenovitě WCDMA.
Abstract:ThisarticlemainlyanalyzesthemaintechnicalcharacteristicsofWCDMA,thedevelopmentstatusandthedirectionoffuturenetworkevolution.ThespecificcharacteristicsandmutualevolutionmethodsofWCDMAtechnologyatdifferentstagesareintroducedrespectively,andthemarketandmainbusinessdirectionsthatWCDMAwillfaceinthefutureareintroduced.ThekeytechnologiesinvolvedintherealizationofWCDMAincluderadiofrequency,intermediatefrequency,basebandRAKEprocessingtechnologyandTurboencodinganddecodingtechnology.Thedifficultiesofdifferenttechnologiesarediscussed.Finally,theprinciplesofenhancedtechnologymulti-userdetectionandsmartantennatechnologyareintroduced.
Klíčová slova: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.
Technické funkce
Jsou uvedeny pouze některé klíčové funkce
Bezdrátová komunikace zabírá šířku pásma 5 MHz
Datový tok je 3,84 MCipů
Podporované režimy multiplexování: FDD,TDD
Vysokorychlostní přenos pro podporu multimediálních služeb
Vnitřní prostředí nejméně 2 Mbit/s
Venkovní procházkové prostředí nejméně 384 kbit/s
Prostředí venkovního vozidla je nejméně 144 kbit/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, jako technologie multiplexování, se nepoužívá pouze pro protokol rozhraní W-CDMA, ale také pro protokol CDMA společnosti Qualcomm.
W-CDMA konkrétně odkazuje na protokol mobilního telefonu definovaný v IMT-2000.
Protokol W-CDMA nemá nic společného s CDMA vyvinutým společností Qualcomm.
Standardní rodina CDMA (cdmaOne a CDMA2000) není kompatibilní se standardní rodinou W-CDMA.
Technologie
W-CDMA může používat nepárová nebo spárovaná frekvenční pásma, ačkoli všechna současná zařízení W-CDMA (jako FOMA a UMTS) používají dvě frekvenční pásma 5 MHz, jedno pro uplink a jedno pro uplinkpoužívá se pro downstream.
Stav vývoje
Trh mobilních komunikací a WCDMA
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.
Používané zdroje symetrického spektra 120MHz (1920MHz-1980MHz, 2110MHz-2170MHz) pro FDD již dříve na schůzce WRC92 pro IMT-2000 a 35MHz (1900 MHz-1920 MHz-201MHz metrický zdroj 201MHz) TDD. Frekvenční pásmo 800 MHz (806–960 MHz), frekvenční pásmo 1,7 GHz (1710–1 885 MHz) a frekvenční pásmo 2,5 GHz (2500-2690MHz) jsme načetli na schůzku WRC2000 pro služby IMT-2000. Přidání těchto dvou vytváří budoucí 3G spektrum 500 MHz výše, obrovský prostor zdrojů je vyhrazen pro budoucí aplikace.
Furthermore,theprocessofglobalintegrationurgentlyneedsagloballyunifiedmobilecommunicationsystem.Theexistingmulti-standardairinterfaceandnetworkequipmentofthesecond-generationmobilecommunicationsystemcannotmeetthisrequirement.Therefore,HighhopesareplacedonthenewWCDMA-FDDmobilecommunicationsystem,whichisexpectedtoachieveglobalharmonization.
Finally,mobilecommunicationtechnologyischangingwitheachpassingday.Thestandardizationandindustrializationofthesecond-generationcommunicationsystemhasbeencompletedforalongtime,anditsmainpurposewasonlytosolvetheneedsofvoicecommunicationatthattime.WiththeincreasingmaturityofwirelesscommunicationtechnologiessuchasCDMAandthedevelopmentofwirelessdatacommunicationtechnologies,theoriginalwirelesscommunicationtechnologysystemneedstobeupdatedaccordinglytoimprovetheutilizationefficiencyofspectrumresourcesandincreasethecostandbenefitofoperators.
3Gstandardizationrequirementsaredrivenbybothmarketandtechnology.3Gstandardformulationandsystemdevelopmenthavebeenbasicallycompleted.Thecommercializationof3Gisalsoinprogress.Theearliestcdma2000-1xinSouthKoreastartedcommercializationattheendof2000,andthecommercializationofWCDMA-FDDinJapanisexpectedtobeginaroundJuly2001.ThecommercializationofWCDMAinChinaandEuropeisplannedtobearound2002.
V roce 2001 byla japonská NTTDoCoMo'sFOMA první komerčně provozovanou službou W-CDMA na světě. J-PhoneJaponskoPhone (nyní SoftwareBank) spustilo službu založenou na W-CDMA s tvrzením, že "Vodafone Global Standard" je kompatibilní s 20 UMTS, zatím ve všech 20 3 verzích. utchisonWhampo postupně provozoval svou síť UMTS (označovanou jako3) globálně.
MostEuropeanGSMoperatorsplantolaunchUMTSservicessometimeinthefuture,althoughseveralhaveputthisserviceontheirschedules,andsomehaveevenstartedoperatingUMTSnetworkssincetheendof2003.VodafonewasputintooperationinmultipleUMTSnetworksinEuropeinFebruary2004.VodafonealsoplanstobuildUMTSnetworksinothercountries(includingAustraliaandNewZealand).AT&TWireless(nowacquiredbyCingularandundertheAT&Tbrand)hasopenedUMTSinsomecities.Althoughtheprogressofthenetworkconstructionhasbeendelayedduetothecompany'smerger,CingularhasannouncedplanstodeployW-CDMAwithHSDPAin2005.
TeliaSonerabegantoprovide384kbpsW-CDMAserviceinFinlandonOctober13,2004.Servicesareonlyavailableinmajorcities.ThecommunicationrateisapproximatelyUS$2permegabyte.
Služba 3G na Tchaj-wanu začala ve čtvrtém čtvrtletí roku 2005. Kromě systémů CDMA2000, ChunghwaTelecom, tchajwanského Velkého bratra, Telecomu na Dálném východě a doslovně telekomu používajících systémy W-CDMA, začala v Asii používat Pacifik Telecom.
ČínaUnicomal začala poskytovat služby W-CDMA v pevninské Číně 17. května 2009 a začala poskytovat služby HSPA (a HSPA+služby v některých oblastech).
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.
Porovnání s jinými standardy
Na začátku bylo CDMA2000 plánováno použít několik 1,25MHz nosičů, ale bylo opuštěno, zatímco W-CDMA používá jeden 5MHz pásmový nosič.
Ve standardu ITUIMT-2000 je W-CDMA považováno za přímé sériové rozprostřené spektrum CDMA a CDMA2000 se nazývá „multi-carrier CDMA“.
Standardní rodina W-CDMA (jako FOMA, UMTS) není v souladu se standardní rodinou CDMA (jako cdmaOne a CDMA2000).
Evoluce
Další vývoj
Aby byly splněny potřeby komercializace a technologického vývoje a zajištěny investice provozovatelů sítí, 3GPP rozdělila standard WCDMA na dva hlavní:
Release99(R99)version:SinceDecember1999,itwillbeupdatedeverythreemonths.TheJune2000versionisbasicallystableandreadyfordevelopment.TheversionsinSeptember,DecemberandMarch2001aremorecomplete;themaininterfacesofthewirelessaccessnetworkIu,Iub,andIuralladoptATMandIPmethods.ThenetworkisanATM-basednetwork;thecorenetworkisbasedontheevolvedGSMMSCandGPRSGSN;Thecircuitislogicallyseparatedfromthepacketswitchingnode.
Verze verze 2000(R00)(byla změněna na verzi 4,5...):Především zavádí "celou IP síť", původně navrhla hlavní síťovou strukturu založenou na IP, nezahájila podstatnou normalizační práci, skutečná "všechny IP" standard se skutečně očekává, aby byla dokončena a kontrola těchto částí sítě bude dokončena v roce 2002. se postupně rozšíří z hlavní sítě (CN) na další rádiovou přístupovou síť (RAN) a terminál (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;
Vývoj systému
Na základě výše uvedeného můžeme shrnout metodu vývoje systému WCDMA takto:
-Release99providesathird-generationfull-networksolution.Thestandardhasmatured,andithastheimplementationfoundation,basicfunctionsandexpansionconditionsofcellularmobilenetworks:
–nová síť bezdrátového přístupu UTRAN
p>–Kombinovaná hlavní síť domény CSandPS
–EnhancedGSMcorenetworkGERAN
-Release4andRelease5furtherincreasenewservices,optimizetechnicalsystemsandThenetworkstructureisthesupplementandimprovementoftheRelease99protocol,whichensuresthecontinuityoftheWCDMAsystem:
–AllIPnetwork
–Nová metoda bezdrátového přístupu – HSDPA
–Vylepšená inteligentní síť a zabezpečení
Technické funkce
Technické funkce
1. Režim synchronizace základnové stanice: podpora asynchronního a synchronního režimu provozu základnové stanice, flexibilní síť
2.Šířka pásma signálu:5MHz;Čipová rychlost:3,84Mcps
3. Režim přenosové diverzity: TSTD (diverzita přenosu s časovým přepínáním),STTD (diverzita přenosu kódování v čase a prostoru), FBTD (diverzita přenosu zpětné vazby)
4.Kódování kanálů:Konvoluční kód a Turbokód, podpora 2Mratedataservice
5.Modulace:Uplink:BPSK;Downlink:QPSK
6.PowerControl:uplinkanddownlinkuvřená smyčka řízení výkonu, vnější smyčka řízení výkonu
7.Režim demodulace: koherentní demodulace za pomoci pilota
8.Kódování hlasu:AMR,kompatibilnísGSM
9.ThecorenetworkisbasedontheevolutionoftheGSM/GPRSnetworkandmaintainscompatibilitywiththeGSM/GPRSnetwork
10.MAPtechnologyAndGPRStunneltechnologyisthecoreofthemobilitymanagementmechanismoftheWCDMAsystem,maintainingcompatibilitywiththeGPRSnetwork
11.PodporaPodporapředáníajemnějšípředání
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.
Přijímač RAKE
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.
Kódování a dekódování kanálů
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.