2023/7/29LaiWeiKuang1

PCSchannelassignmentandhandoverschemes

賴威光中山大學(xué)資工系高速網(wǎng)路實(shí)驗(yàn)室wklai@.tw2023/7/29LaiWeiKuang2報(bào)告綱要

背景及研究介紹SystemAspectsofCellularRadioChannelAssignmentAlgorithms

問題及提出方法結(jié)論

2023/7/29LaiWeiKuang3SystemAspectsofCellularRadio

Therearetwomaincomponentsinmobileradiosystems:

>theradiointerface

>afixednetworkWhatmakespubliccellularradiocomplex?

>thecontrolstructureThenumberofusersanetworkcansupportisfundamentallydependentontheCommonAirInterface(CAI)overwhichuserscommunicate.2023/7/29LaiWeiKuang4Otherfacts:

>theamountofspectrumtheregulatorsallocate

>thesizeoftheradiocoverageareafromaBS

>theamountofinterferenceaparticularradiolinkcantolerate.2023/7/29LaiWeiKuang5SystemPlanninginFirst-andSecond-GenerationSystemsHandOff

>Signalingbetweenthemobile,theBSs,

andcontrolcentersCluster

>formedbycell(s)

>usestheentireallocatedspectrum.Co-channelinterference

>usingthesamechannelbetweentwomobiles.

>iscontainedtoacceptablelimitsbythedistancebetween

thecells.2023/7/29LaiWeiKuang6SystemPlanninginFirst-andSecond-GenerationSystemsIfthecellsizesaredecreasedwhichcausesacorrespondingreductioninclustersize,thenumberofchannelsperunitareaincreases.Themosteffectivewayofincreasingnetworkcapacityistodecreasethecellsize,butthecomplexityofthenetworkinfrastructureincreases.2023/7/29LaiWeiKuang7GrowthScenariosInthestart-upphaseofacellularnetwork,capacityisnottheproblem.Asthenetworkmatures,capacitybecomesincreasinglyimportant.Clustersizeisdecreasedwhilemaintainingsignal-to-interferenceratios(SIRs)thatensurethatlinkqualityisacceptable.SectorizationgenerallyresultsinanincreaseinSIR.Sectorizationmustbeintroducedwithdecreasingofclustersize.2023/7/29LaiWeiKuang8GrowthScenariosTheminimumacceptableSIR(SIRmin)issystem-specific.Byusingdiscontinuoustransmission(DTX),frequencyhopping(FH)ofthecarrierandpowercontrol,suchsystemscanallowlowerSIRmin.2023/7/29LaiWeiKuang9Microcells"Microcells"areusedinCT-2,PCSandDECT.Conventionalmicrocellsareinterconnectedtomobileswitchingcenterstypicallyinastarconfigurationviastandardtransmissionfacilities,suchas1.5Mb/s(North-AmericanTIStandard)or2Mb/s(European)links.Somemicrocellsareessentially"remoteradiationsites".2023/7/29LaiWeiKuang10HandOverIssuesinFDMAandTDMAHandOver(HO),orHandOffistheswitchingprocedurewhenanMSchangesitscommunicationfromoneBStoanadjacentonewhenthereceivedsignaldecreasesbelowasystemthreshold.TherearetwotypeofHO:

SoftHO(SHO)andHardHO(HHO).HHO:

>breakbeforemake.

>communicationsofaMSwithaBSareservedbeforetheyarere-establishedwiththenewBS.2023/7/29LaiWeiKuang11HandOverIssuesinFDMAandTDMASHO:>boththeexistingBSandtheBSthatwillultimatelyassumeresponsibilityforthecallcommunicatesimultaneouslywiththeMS.PreparingforanHO:

>thedecisionwhenandwheretoHOmustbemade.

>boththehandsetandthenetworkmustswitch.Thedecisionalgorithmtypicallyusesmeasurementsofreceivedsignalstrengthindication(RSSI)andbiterrorrate(BER)todetecttheneedtoHOandmustidentifyafreechannelinaneighboringcell.2023/7/29LaiWeiKuang12HandOverIssuesinFDMAandTDMAPrioritizedHOschemes:

>someaimtominimizeboththeprobabilityofforcedterminationofcallsinprogressduetoHOfailures,andthedegradationinspectrumutilization.

>othersaimatbalancingordissipatingtheteletrafficloadacrossneighboringcells.2023/7/29LaiWeiKuang13DCAinFDMAandTDMASystemsFCA:FixedChannelAssignment.DynamicChannelAssignment(DCA)caninprincipleoperatewithFDMAorTDMAandwithonlymodestenhancementstosecond-generation.TheassignmentofchannelsmaybedonebyasystemthatadaptstoboththetrafficloadingattheBSandtheinterferenceonthechannels.2023/7/29LaiWeiKuang14DCAinFDMAandTDMASystemsTraffic-adaptivesystem:

>channelborrowing:inatraffic-adaptivesystem,whenacellisoverloaded,itcanuseidlechannelofitsneighboringcell.

>Markovallocation:assignstoeachnewcallthefirstunusedandnon-interferencechannelinanorderspecifictothecorrespondingcell-site.2023/7/29LaiWeiKuang15DCAinFDMAandTDMASystemsInterference-adaptivesystem:

>lendsitselftodistributedDCAalgorithmsthatareabletoself-organize.

>TheMScontrolsthechannelassignmentofacallwithouttheneedtocommunicatewithotherBSsorwithacentralcontroller.Thechoiceamongacceptablechannelsisanimportantissue:

choosingtheleast-interferedchannelprovidesmostrobustquality,whileselectionaccordingapre-definedordermayleadtogreatcapacity.2023/7/29LaiWeiKuang16DCAinFDMAandTDMASystemsByspecifyingtheSIRthresholdstobehigherthantheminimumrequiredforgoodlinkquality,robustnessagainstmeasurementanddecisionerrorsmaybeachieved.AsimplealgorithmusedintransmitterpowercontrolisforeachusertoincreaseitstransmitpowerwhentheSIRisinadequateandtodecreasetheSIRwhenitismorethanadequate,andthissucceedswheneverthereisanysetofpowerlevelsthatallowallthestationstoachieveanadequateSIR.2023/7/29LaiWeiKuang17DCAinFDMAandTDMASystemsPowercontrolgreatlyenhancesperformance,andtheDCAprocessneednotcauseunacceptablechannelreassignmentorcall-failurerateseveninthepresenceofhighuserdemand.Thebestwayofintegratinginterference-adaptivepowercontrolwithchannelassignmentiscurrentlyunknown.ImportantissuesofDCA:

>re-assignmentmaybenecessary.

>Delaymustbecontrolled.

>SIRmeasurementandchannel-searchtechniques.

>TDMA-basedDCArequiresbase-to-basesynchronyforfullcapacitygain.2023/7/29LaiWeiKuang18CodeDivisionMultipleAccessCDMASystemsOfparamountimportanceisthefactthatCDMAusessingle-cellclusters.NofrequencyplanningisrequiredinCDMAnetworksduetotheon-cellclusterswhichallusethesamecarrierfrequency.SHOisusedinCDMAtoavoidnear-farproblemsatthecell-edgeduetocell-membershipambiguity.SofterSHO(SSHO)isusedbetweensectorsofthesamecell.2023/7/29LaiWeiKuang19ChannelAssignmentAlgorithms

PCS網(wǎng)路架構(gòu)PCS網(wǎng)路資源WirelessResourceWiredResourceMobilityManagementResourceCellsforfrequencyreuse2023/7/29LaiWeiKuang202023/7/29LaiWeiKuang21Channel的分配要求Hand-offchannelassignmentrequestInitialcallchannelassignmentrequestChannel不足所造成的影響ForcedterminationBlockedcall

2023/7/29LaiWeiKuang22

連線品質(zhì)“對(duì)一個(gè)Mobileuser而言,從連線建立至連線由使用者自行中斷期間,所有有關(guān)Channelassignment的動(dòng)作均成功的機(jī)率”己被提出的NPS,RCS,FIFO,MBPS均以上述定義作效能比較標(biāo)準(zhǔn),而為了比較這些演算法和本文所設(shè)計(jì)的演算法效能,亦採用這個(gè)定義

10Pf+Po2023/7/29LaiWeiKuang232023/7/29LaiWeiKuang24己被提出的分配演算法NPS(Non-PrioritizedScheme)RCS(ReservedChannelScheme)QueuingPriorityScheme(QPS)MBPSFIFOGeneticAlgorithms

2023/7/29LaiWeiKuang25

NPS演算法Non-PrioritizedScheme(NPS)：把Handoffchannelassignment和Initialcallchannelassignment視為相同，當(dāng)cell中有channel即配予，沒有分ForcedTermination和BlockedCall。不對(duì)任何channel配置要求作queuing的動(dòng)作2023/7/29LaiWeiKuang26

RCS演算法ReservedChannelScheme(RCS)：把每個(gè)cell內(nèi)的channels分為二組，一組可分配給Handoff和Initialcall另一組只保留給Handoff2023/7/29LaiWeiKuang27Handoffarea介紹右圖在兩個(gè)cell重疊的部分稱handoffarea，因?yàn)閔andoffarea的存在，使得handoff的channel配置要求在沒有channel可被予時(shí)，可先被queuing起來。因?yàn)樵趆andoffarea中,可同時(shí)使用兩個(gè)cell的channel，當(dāng)目的cell目前沒有可用的channel，則暫時(shí)保留handoff的動(dòng)作，使用原所在cell配予的channel。先把handoff要求送至目的cell的basestation的服務(wù)queue中(在MS越過handoffarea前)等待目的cell有channel被釋放，再行完成handoff的動(dòng)作。藉以降低ForcedTermination的機(jī)會(huì)。FIFO,MBPS即針對(duì)handoffarea的特性而設(shè)計(jì)2023/7/29LaiWeiKuang28

FIFO、MBPS演算法這兩種演算法均是利用handoffarea的特性其中queue可為FirstInFirstOut(FIFO)，或以計(jì)算MS越過handoffarea程度(即原先所在cell的訊號(hào)強(qiáng)度)，來決定配予channel先後的priority，稱Measure-BasePriorityScheme(MBPS)。2023/7/29LaiWeiKuang29問題及提出方法上述演算法的盲點(diǎn)對(duì)blockedcall和forcedtermination沒有取捨的標(biāo)準(zhǔn)演算法只對(duì)handoff的channel配置要求作queueing處理,無法適用各種不同trafficload的狀態(tài)2023/7/29LaiWeiKuang30

研究過程及提出方法建立blockedcall和forcedtermination取捨的標(biāo)準(zhǔn)利用分析數(shù)學(xué)模組,得到分配initialcall和handoff這兩種channel配置要求的最佳比例使系統(tǒng)能維持在,當(dāng)時(shí)channel資源所能提供的最佳連線品質(zhì)要控制handoff和initialcall這兩種channel配置要求比例,必須提供initialcallqueuing的機(jī)構(gòu)2023/7/29LaiWeiKuang31Pc

=(theprobabilitythatachannelisavailableforinitialaccess)*(theprobabilitythateveryhandoffaccessissuccessfulduringthecallholdingtime)

(7)

Pc’

=(1-Po)(1–Pf)E[k]Poinitialcallchannel配置要求失敗機(jī)率

Pfhandoffchannel配置要求失敗機(jī)率E[k]istheexpectednumberofhandoffsduringthecallholdingtimeiftheinitialcallisnotblockedandisnotforcedterminatedduringhandoffs

2023/7/29LaiWeiKuang32Theapproximationtothecallcompletionprobability,Pc’,hasthenicepropertyofeasiercomputationandmanipulation.Whentheproportionofthehandoffcallsandtheinitialcallsisw:1(x=(w/(w+1))y),thealternativecallcompletionprobability,Pc’,hasthemaximumvalue.Pc’=c/o,whereE[k]=w=.(13)2023/7/29LaiWeiKuang33

最佳的分配比例在實(shí)際的系統(tǒng)是不可能達(dá)到的ThequeuesizemustbelargeenoughThetime-outforahandoffcallcannotbeadjustedThetime-outforaninitialcallcanbeadjustedwithintolerableranges2023/7/29LaiWeiKuang34

趨近最佳化分配的演算法設(shè)計(jì)SinglequeueorDualqueuesFIFOorPriorityqueue以initialcalltime_outvalue或StatisticalMultiplexing來趨近最佳分配2023/7/29LaiWeiKuang35

SFTT演算法單一貯列(Singlequeue)channel要求服務(wù)順序?yàn)橄冗M(jìn)先出(FIFO)要求被完成有時(shí)限(Timeout)以給予initialcall時(shí)限(Timeout)值大小,服務(wù)兩種channel配置要求的比例趨近最佳分配2023/7/29LaiWeiKuang36

SPTT演算法單一貯列(Singlequeue)服務(wù)順序以優(yōu)先權(quán)(Priority)大小為順序要求被完成有時(shí)限(Timeout)以給予initialcall時(shí)限(Timeout)值大小,服務(wù)兩種channel配置要求的比例趨近最佳分配2023/7/29LaiWeiKuang37

DFTS演算法二個(gè)貯列(Dualqueue)channel要求服務(wù)順序?yàn)橄冗M(jìn)先出(FIFO)要求被完成有時(shí)限(Timeout)以統(tǒng)計(jì)式多工(StatisticalMultiplexing)方式控制最佳分配率2023/7/29LaiWeiKuang38

DPTS演算法二個(gè)貯列(Dualqueue)服務(wù)順序以優(yōu)先權(quán)(Priority)大小為順序要求被完成有時(shí)限(Timeout)以統(tǒng)計(jì)式多工(StatisticalMultiplexing)方式控制最佳分配率2023/7/29LaiWeiKuang39

(a)Theforcedterminationprobability.(b)Thenewcallblockingprobability.

(C)Thecallincompletionprobability.Figure10.Performanceofsixschemes.ThemeanMSresidencetimeis30minutes.Themeancallholdingtimeis3minutes.Themeandegradationintervalis18seconds.Thenumberofchannelsineachcellis50

2023/7/29LaiWeiKuang40Figure12.TheSFTTschemewithdifferent1/

underlightload

2023/7/29LaiWeiKuang41

結(jié)論(1)Givingprioritytohandoffcallsoverinitialcallswouldnotyieldbettercallcompletionprobabilitiesingeneral

(2)Theproportionsofhandoffcallsandinitialcallswillinfluencethecallcompletionprobabilities2023/7/29LaiWeiKuang42(3)Theimplementationofthepriorityschemehastheeffectofdecreasingthecallincompletionprobabilities.However,itmightalsohavethenegativeeffectofincreasingtheforcedterminationprobabilities.

2023/7/29LaiWeiKuang43(4)TheimplementationofthestatisticalTDMhastheeffectofdecreasingthecallincompletionprobabilitieswhentheaveragenewcallarrivalratesarehigh.Itisbecausewhentherearemanynewcalls,theratioofinitialcallsandhandoffcallsservedcanbetunedwiththestatisticalmultiplexing.

2023/7/29L