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LTE,theradiotechnologypathtowards4GM.Rinnea,,andO.Tirkkonena,baNokiaResearchCenter,P.O.Box407,FIN-00045NokiaGroup,FinlandbDepartmentofCommunicationsandNetworking,AaltoUniversity,P.O.Box13000,FIN-00076Aalto,FinlandAvailableonline7July2010.AbstractEvolvedUniversalTerrestrialRadioAccess(EUTRA),knownastheLongTermEvolution(LTE)technology,bringscellularcommunicationtothefourthgeneration(4G)era.Inthisarticle,wediscussthemostimportantcharacteristicsofLTE;itssimplifiednetworkarchitecturewhichallowsultimatemeansforadaptationoftheradiotransmissiontotheInternetpackettrafficflowsandtothevaryingchannelstates.LTEradioresourcemanagementisbasedontime–frequencyscheduling,fastfeedbackbetweenthetransmitterandreceiver,andnearlyoptimaladaptationoftransportformats.Yet,theradiosystemissimpleandcostefficienttomanagefromtheevolvedpacketcorenetwork,havingaserverarchitecturewithIPtunnels.ThemobilitystatesandresourceallocationallowpowersaveoperationoftheUserEquipmentwhennotactivelycommunicating.Inaddition,webriefthekeyresultsontheLTEbaselineperformanceforpairedandunpairedfrequencybands,i.e.thetwoduplexmodes.Keywords:EUTRA;LTE;RadioAccessNetwork;RadioResourcemanagement;PerformanceevaluationArticleOutline1.Introduction2.LTEarchitecture2.1.UEstatesofoperation2.2.Evolvedpacketsystem2.3.LTEinterfaces2.4.Addressing2.5.Qualityofservice3.EUTRANprotocols4.Physicallayer4.1.Channelcharacterization4.2.Cyclicprefix4.3.Downlink:OFDMA4.4.Uplink:SC–FDMA4.5.Multiantennatechniques4.6.Modulationandchannelcoding4.7.Numerologyandframestructure4.8.Bandwidthandduplexing5.Radioresourcemanagement5.1.Powercontrol5.2.Linkadaptation5.2.1.Adaptivecodingandmodulation5.2.2.Rankadaptation5.2.3.Adaptiveretransmissions5.2.4.Adaptivetransmissionbandwidth5.3.Inter-cellRRM5.4.Scheduling5.5.Handover5.6.Powersavingmodes6.Systemperformance6.1.Aboutthemodelingandsimulations6.2.Spectralefficiencyandcapacityanalysis7.ConclusionsAcknowledgementsReferences1.IntroductionTheterm“LongTermEvolution”(LTE)standsfortheprocesstogenerateanovelairinterfacebythe3rdGenerationPartnershipProject(3GPP),andforthespecifiedtechnology.Earlier,the3GWidebandCodeDivisionMultipleAccess(WCDMA)providedanew,highcapacity,airinterfaceincludingtransportofpackettraffic,andtheRadioAccessNetwork(RAN)designedtobecompatiblewiththesecondgenerationGSMandGPRScorenetworks.WCDMAallowsmultiplexingofvoiceandvariableratedataservices,anditsevolutiontoHighSpeedPacketAccess(HSPA)[1]and[2]furtherenhancesthehighratepacketcapabilitiesasasetofnewtransportchannels.LTEwasinitiatedasastudyitemanditstechnicalrequirementswereagreedinJune2005[3].ThetargetsofLTEincludedreducedlatency,higheruserdatarates,improvedsystemcapacityandcoverageandreducedcostofoperation.LTEwasrequiredtobecomeastand-alonesystemwithpacket-switchednetworking.Thestudyitemwasreportedthefirsttimeinthetechnicalreport[4],whereitwasdecidedthatLTEisbasedonanewairinterface,differentfromtheWCDMA/HSPAenhancements.Theactualspecificationworkresultedinacompletesetofapprovedstandardspecifications[1]and[5]thatarematureenoughforproductimplementation.TheevolutionoftheLTEsystem,itsarchitecture,protocolsandperformancearedescribedwidelye.g.in[6],[7],[8]and[9].ThesalientcharacteristicsofLTEareasfollows:aflatarchitecturebasedondistributedservers,LTEbasestationshavingtransportconnectionstothecorenetworkwithoutintermediateRANnetworknodes(suchasradionetworkcontrollers).Simplifiedandefficientradioprotocols,wherechannelstateinformationisavailableattheradioprotocolpeerstooptimizetheaccessandtominimizetheoverhead.Aphysicallayerdesignfavouringfrequencydomainprocessingforefficiency,enablinghighdataratetransmissionse.g.bymultiantennatransmissionmethods,andalleviatinginterferenceconditionsbyintracellorthogonality.Radioresourcemanagementenablingscalabilityoftransmissionbandwidth(BW),andahighdegreeofmultiuserdiversitye.g.bytime–frequencydomainscheduling.EfficientoperationinpowersavingmodesasadesignedfundamentalpropertyoftheUserEquipment(UE).Inthispaper,wediscussLTEtechnologyandhowitssolutionswillmeetthetargetsthatweresetfortheInternationalMobileTelecommunication(IMT)systems.Evenmore,LTEmeetsthetargetsalsoforIMT-Advanced[10]incertainevaluationscenarios,andisthefoundationofnewreleasesofLTEspecification[11],aimingtomeettheIMT-Alocalareaenvironmenttargets.The3GPPapproachto4GsystemsisthusbasedonLTE.Thepaperisorganizedasfollows:ThearchitectureofLTEisdiscussedinSection2andtheprotocolsinSection3.ThephysicallayersolutionsarepresentedinSection4,andtheRadioResourceManagementprinciplesinSection5.SystemperformanceresultsarebriefedinSection6andthepaperisconcludedinSection7.2.LTEarchitecture2.1.UEstatesofoperationInLTE,theUEmayoperateintwostates,theLTE_IdleortheLTE_Activestate,inrelationtothenon-accessstratumwhichconnectstheUEandthecorenetwork.Intheradioaccessnetwork,thesecorrespondtotheRadioResourceControl(RRC)statesRRC_IdleandRRC_Connected,respectively[1].Themobilitystatemachineisconsiderablysimplifiedfrom3G/WCDMAUTRAN(withatleastfourstates).Discontinuoustransmissionandreceptionmodesapplytobothstates,enablinge