LTE網(wǎng)絡(luò)優(yōu)化方案：上下行鏈路不均衡的優(yōu)化分析

#864000001234Log-normalstd.dev.ofDL/ULimbalance[dB]Offset——BalanceB——tJ—864000001234Log-normalstd.dev.ofDL/ULimbalance[dB]Offset——BalanceB——tJ—_b0%CCH:芒二10%CCH■]嚴土20%CCH30%CCH20Figure8comparesthesystemcapacity.AsshowninFig.8(a),offsettingprovideslesscapacityinCase1whensomeCCHoverheadisconsidered.ThisismainlyduetothelargerCCHoverheadcausedbyIor/(Ioc+N0)degradationataroundcelledge.However,asshowninFig.8(b),offsettingprovideslargercapacitythanbalancinginCase3.Thecapacityisabout20%largerat2dBimbalanceand10%CCHoverhead.Thisisbecausebalancingreducesthetotalpowerandhenceincreasestheimpactofthermalnoise.Withoffsetting,theimpactofthermalnoiseiskeptatminimum.Therefore,offsettingisbeneficialinprovidinglargercapacityinmoderate/largecellscenarios(moreevidentinthermalnoiselimitedscenarios).01234Log-normalstd.dev.ofDL/ULimbalance[dB]186420000EEsypuucIN0(a)(b)(a)Fig.8Normalisedcapacityfor(a)Case1and(b)Case3.BenefitsofcellspecificoffsetsSummarisingabovediscussionsandanalysis,thebenefitsofcellspecificoffsetsare:Offsettingprovideslargersystemcapacitywhencellsizeismoderate/large(i.e.,moreevidentinthermalnoiselimitedscenarios);OffsettingallowstheoperatortoflexiblychoosebetweenULoptimisedandDLoptimised;EasytooperateastheoffsetisjustaparameteronBCCH(orDCCH),anddoesnotinvolvecomplicatedpoweradjustments.NotethatbalancingbyDLtransmissionpoweradjustingisanywaypossible,regardlessofsupportforanoffsetmechanism.ThemechanismtoutilisecellspecificoffsetsallowstheoperatortocopewithDL/ULimbalanceinvariousways,providingflexiblecountermeasuresdependingonthedeploymentscenario.Withouttheoffsettingmechanism,theoperatorisrestrictedtoeithertoleratingULlosses,ortoengageacomplicatedprocessofadjustingDLtransmissionpowers.Therefore,theoffsettingmechanismshouldbesupportedinLTE.ReadingneighbourBCH3.1WaysofsignallingcellspecificoffsetsInsection2,theneedforcellspecificoffsetshasbeenjustified.ThequestionthenbecomeshowtheoffsetvaluesaresignalledtotheUE.Asdiscussedin[2],therearetwoways:Alt.l:UEreadsoffsetincludedinneighbourBCH一TheoffsetissetforitsowncellinBCH(noneedtocareaboutneighbours).一Thesameoffsetappliestoalltheneighbouringcells(1-to-all).一TheUEhastoreadtheneighbourBCHtoavoidanyping-pongs[5].一ThiswasdecidedasmandatoryinRAN2#58inKobe,butreopenedinRANPlenary#36.Alt.2:UseNCL一TheoffsetsapplicabletotherelevantneighboursarebroadcastbyNCL.一Theoffsetcanbespecifictocertainserving-neighbourrelationship(1-to-1).一TheuseofNCLcauseslargeroverheadcomparedtoAlt.1.一NCLneedstobeplannedandsetbyOAM,whichcanbecomplicated.一ThisisalreadysupportedoptionallyinLTE(RAN2decision).TheonlyquestionthatneedstobeaddressediswhetherLTEshallsupportAlt.1ornot.ConcernsofreadingneighbourBCHAsdiscussedindetailin[2]andaboveinsection2,theoffsetcanbeusedprimarilytomitigateDL/ULimbalance.Assuchitisprevalentthateachcellrequiresadifferentoffsetvalue,andthatitissufficientformostcasesiftheoffsetis1-to-all.Thatis,the1-to-1granularityisnotnecessarytocopewithDL/ULimbalance,butonlynecessaryinirregularcasesliketunnels.Hence,itwouldbepreferable,fromOAMaspects,thatAlt.1isadopted.However,asexpressedbyandinparticular[3],thereareseveralconcernsofmandatingtheUEtoreadneighbourBCH:UEwillhavetoreadBCHforeachcelldetected;一ItcanbebatteryconsumingiftheUEcannotdecodeBCHandrepeatedlytriesdecodingforadetectedcell;一ThisproblemismoreevidentiftheBCHerrorratedoesnotmatch(isworsethan)thecelldetectionperformance;Note:ThismaybepreventedtosomeextentbyspecifyingUEbehaviours,e.g.,UEonlyreadsBCHifRSRP>threshold,and/orUEconsidersoffset=0ifitfailsreadingBCHaftersomeattempts.UEimplementationmaybemorecomplex.一UEmayhavetodecidewhethertoreadBCHornotupondetectingacell,e.g.,UEdoesnothavetoreadforcellsindicatedinNCLorifRSRP<threshold,etc.LargerBCHoverheadtomakeitrobust.一E.g.,byreducingthecodingrate,increasingTxpower,repetition,softcombining,etc.TheseaspectsneedtobediscussedinRANWGs,andcommentsfromUEvendorsareespeciallyvaluableinthisrespect.Iftheseconcernsareserious,LTEshouldcertainlynotsupportreadingofneighbourBCH.OtheraspectsofreadingneighbourBCHIndiscussingthepros/consofreadingneighbourBCH,anotheraspectthatmightbeworthconsideringistheCSGcell(home-eNB)scenario.TherequirementsofCSGcells[6]statenotably:ItshallbepossibletominimisethequantityofmeasurementswhichUEsperformonCSGCells,iftheUEdoesnotbelongtotheUserGroupofaspecificCSGCell.Themobilityproceduresshallallowalargenumberof(small)CSGCellstobedeployedwithinthecoverageofe-UTRAN,UTRANandGERANmacro-layercells.Deploymentof(additional)CSGCellsshallnotrequirereconfigurationofothereNodeB(E-UTRAN)orRNC(UTRAN)orBSS(GERAN).ThiscouldbeeasilyachievediftheUEreadstheBCHofadetectedcell,andfindsoutthatthecellisnotopentopublicthroughsomesimpleindicatorsorcellidincludedinBCH.ThiswillallowtheUEtoomitmeasurementsonthatcell,andavoidreportingonCSGcellsthatithasnoaccessto.IftheUEdoesnotreadneighbourBCH,othermeansmustbethoughtof,althoughapproachessuchasblacklistingseemstocontradictwithrequirement#8above.ConclusionsTheneedforcellspecificoffsetmechanismandconcernsofreadingneighbourBCHhavebeendiscussed.Followingthediscussionsaboveandin[2],weseeonlytwoviablealternativesshowninTable2.Table2.Viablealternatives[2].AlternativeAlternative1Alternative2IntrafrequencyIDLEmodemobilityTheUEismandatedtoreadtheP-BCHforeachcellthathasbeendetectedandappliestheoffsetvaluesbroadcasttherewith(Solution3).Tocopewithexceptionalcases,e.g.,indoors,tunnels,highspeedtrains,prohibitingcellsseenacrossabay/channel,NCLisalsooptionallysupportedoverD-BCH(Solution2).AnNCL(typicallyamodestlist)canbeprovidedoptionallyfromtheservingcellusingD-BCH.TheUEappliestheoffsetvaluesincludedintheNCL.ACTIVEmodemobilityThesameasIDLEmodemobility.TheUEconsiderstheoffsetvaluesofallthedetectedneighboursintriggeringmeasurementreports.AnNCL(typicallyalargelistincludinggranularoffsetvalues)canbeprovidedfromtheservingcellusingDCCH.TheUEappliestheoffsetvaluesincludedintheNCLintriggeringmeasurementreports.Inter-frequency/RATLayerspecificparameters(i.e.,parameterscommontoallthecellsonthefrequencylayer)aresupported.Tocopewithexceptionalcases,NCLisalsooptionallysupportedoverD-BCH(Solution2).ThesameasAlternative1(buttheNCLmaybesentbyDCCHinsteadincaseofACTIVEmode).OAMcomplexityLowerHigherOverheadLowerHigherUEcomplexityHigherLowerAfterrevisitingtheissue,ourcurrentpositionisasbelow:Anoffsetmechanismisnecessary.ThecurrentRAN2WAtosupportoptionalNCLtosetserving-neighbourpairwisespecificoffsetsshouldbekept.TheoptionalNCLshouldalsobesupportedforinter-frequency/RATneighbourcells[2].ThesolutionsforACTIVE/IDLEmobilityshouldbealigned[2],i.e.,thechoiceshouldonlybebetweenAlt.1andAlt.2inTable2.IfreadingofneighbourBCHhasseriousimpactsonUEcomplexity/batteryandsystemperformance,Alt.2inTable2shouldbeadopted.OtherwiseAlt.1shouldbeadopted.Toprogressthisissueand