通信工程外文文献

外文资料与中文翻译外文资料：ReviewofUMTS1.1UMTSNetworkArchitectureTheEuropean/Japanese3GstandardisreferredtoasUMTS.UMTSisoneofanumberofstandardsratifiedbytheITU-TundertheumbrellaofIMT-2000.Itiscurrentlythedominantstandard,withtheUSCDMA2000standardgainingground,particularlywithoperatorsthathavedeployedcdmaOneastheir2Gtechnology.Attimeofwriting,Japanisthemostadvancedintermsof3Gnetworkdeployment.Thethreeincumbentoperatorstherehaveimplementedthreedifferenttechnologies:J-PhoneisusingUMTS,KDDIhasaCDMA2000network,andthelargestoperatorNTTDoCoMoisusingasystembrandedasFOMA(FreedomofMultimediaAccess).FOMAisbasedontheoriginalUMTSproposal,priortoitsharmonizationandstandardization.TheUMTSstandardisspecifiedasamigrationfromthesecondgenerationGSMstandardtoUMTSviatheGeneralPacketRadioSystem(GPRS)andEnhancedDataforGlobalEvolution(EDGE),asshowninFigure.ThisisasoundrationalesinceasofApril2003,therewereover847MillionGSMsubscribersworldwide1,accountingfor68%oftheglobalcellularsubscriberfigures.TheemphasisisonkeepingasmuchoftheGSMnetworkaspossibletooperatewiththenewsystem.WearenowwellontheroadtowardsThirdGeneration(3G),wherethenetworkwillsupportalltraffictypes:voice,videoanddata,andweshouldseeaneventualexplosionintheservicesavailableonthemobiledevice.ThedrivingtechnologyforthisistheIPprotocol.Manycellularoperatorsarenowatapositionreferredtoas2.5G,withthedeploymentofGPRS,whichintroducesanIPbackboneintothemobilecorenetwork.Thediagrambelow,Figure2,showsanoverviewofthekeycomponentsinaGPRSnetwork,andhowitfitsintotheexistingGSMinfrastructure.TheinterfacebetweentheSGSNandGGSNisknownastheGninterfaceandusestheGPRStunnelingprotocol(GTP,discussedlater).Theprimaryreasonfortheintroductionofthisinfrastructureistoofferconnectionstoexternalpacketnetworks,suchastheInternetoracorporateIntranet.ThisbringstheIPprotocolintothenetworkasatransportbetweentheSGSNandGGSN.Thisallowsdataservicessuchasemailorwebbrowsingonthemobiledevice,withusersbeingchargedbasedonvolumeofdataratherthantimeconnected.Thedominantstandardfordeliveryof3GnetworksandservicesistheUniversalMobileTelecommunicationsSystem,orUMTS.ThefirstdeploymentofUMTSistheRelease’99architecture,shownbelowinFigure3.Inthisnetwork,themajorchangeisintheradioaccessnetwork(RAN)withtheintroductionofCDMAtechnologyfortheairinterface,andATMasatransportinthetransmissionpart.Thesechangeshavebeenintroducedprincipallytosupportthetransportofvoice,videoanddataservicesonthesamenetwork.Thecorenetworkremainsrelativelyunchanged,withprimarilysoftwareupgrades.However,theIPprotocolpushesfurtherintothenetworkwiththeRNCnowcommunicatingwiththe3GSGSNusingIP.ThenextevolutionstepistheRelease4architecture,Figure4.Here,theGSMcoreisreplacedwithanIPnetworkinfrastructurebasedaroundVoiceoverIPtechnology.TheMSCevolvesintotwoseparatecomponents:aMediaGateway(MGW)andanMSCServer(MSS).Thisessentiallybreaksaparttherolesofconnectionandconnectioncontrol.AnMSScanhandlemultipleMGWs,makingthenetworkmorescaleable.SincetherearenowanumberofIPcloudsinthe3Gnetwork,itmakessensetomergethesetogetherintooneIPorIP/ATMbackbone(itislikelybothoptionswillbeavailabletooperators.)ThisextendsIPrightacrossthewholenetwork,allthewaytotheBTS.ThisisreferredtoastheAll-IPnetwork,ortheRelease5architecture,asshowninFigure5.TheHLR/VLR/EIRaregeneralisedandreferredtoastheHLRSubsystem(HSS).Nowthelastremnantsoftraditionaltelecommunicationsswitchingareremoved,leavinganetworkoperatingcompletelyontheIPprotocol,andgeneralisedforthetransportofmanyservicetypes.Real-timeservicesaresupportedthroughtheintroductionofanewnetworkdomain,theIPMultimediaSubsystem(IMS).Currentlythe3GPPareworkingonRelease6,whichpurportstocoverallaspectsnotaddressedinfrozenreleases.SomecallUMTSRelease64GanditincludessuchissuesasinterworkingofhotspotradioaccesstechnologiessuchaswirelessLAN.1.2UMTSFDDandTDDLikeanyCDMAsystem,UMTSneedsawidefrequencybandinwhichtooperatetoeffectivelyspreadsignals.Thedefiningcharacteristicofthesystemisthechiprate,whereachipisthewidthofonesymboloftheCDMAcode.UMTSusesachiprateof3.84Mchips/sandthisconvertstoarequiredspectrumcarrierof5MHzwide.Sincethisiswiderthanthe1.25MHzneededfortheexistingcdmaOnesystem,theUMTSairinterfaceistermed‘wideband’CDMA.ThereareactuallytworadiotechnologiesundertheUMTSumbrella:UMTSFDDandTDD.FDDstandsforFrequencyDivisionDuplex,andlikeGSM,separatestrafficintheuplinkanddownlinkbyplacingthematdifferentfrequencychannels.Thereforeanoperatormusthaveapairoffrequenciesallocatedtoallowthemtorunanetwork,hencetheterm‘pairedspectrum’.TDDorTimeDivisionDuplexrequiresonlyonefrequencychannel,anduplinkanddownlinktrafficareseparatedbysendingthematdifferenttimes.TheITU-Tspectrumusage,asshowninFigure6,forFDDis1920-980MHzforuplinktraffic,and2110-2170MHzfordownlink.Theminimumallocationanoperatorneedsistwopaired5MHzchannels,oneforuplinkandonefordownlink,ataseparationof190MHz.However,toprovidecomprehensivecoverageandservices,itisrecommendedthatanoperatorbegiventhreechannels.Consideringthespectrumallocation,thereare12pairedchannelsavailable,andmanycountrieshavenowcompletedthelicencingprocessforthisspe