A Cooperative TDMA MAC协作TDMA的mac 协议

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ACooperativeTDMAMACProtocolusingDynamicSlotAssignmentSchemeJong-KwanLee,Hong-JunNohandJaesungLimTacticalNetworkResearchCenterAjouUniversitySuwon,SouthKorea{jklee64,nonoboy,jaslim}@ajou.ac.krAbstractInthispaper,weproposeandanalyzeacooperativeproposedforenablingcooperativetransmissioninRayleighTDMAMACprotocolwithdynamicslotassignment.Ourproto-fadingchannelsandforimprovingtheprobabilityofcorrectcolallowsasourcenodetoretransmitfailedpacketcooperativelypacketreceptionandsystemthroughput.TheproposedC-duringaneighbornodesidleslot.ThesourcenodecanselectTDMAimprovesthethroughputofconventionalTDMAbyidleslotsforacooperativeretransmissionbyasimplecontrolpacketexchangeamongneighbornodes.Theneighbornodesthatover40%.havethefailedpackettransmitduringtheselectedslotattheOntheotherhand,manydynamicslotassignemnetschemessametime.Iftherearenoidleslotsavailable,thecooperativehavebeenproposedforadhocnetworks[8-12].USAP[8]retransmissionisattemptedduringthesourcenodestimeslot.reservesthefirstslotofeachframeforsignaling.ItallowsThethroughputofTDMAcanbesignificantlyimprovedbynodestoassignslotdynamicallyusingthereservedslot,buttheproposedcooperativeretransmissionschemeattheexpenseofincreasedoverhead.Weformulateananalyticmodelforslotutilizationisverylowduetoitsfixedframelength.USAP-theproposedprotocolforimplementationoverRayleighfadingMA[9]isanextensionversionofUSAPthatutilizesanchannelsandvalidateitbysimulation.Theresultsshowthattheadaptivebroadcastcycle(ABC)tochangetheframelengththroughputofTDMAsystemsisimprovedsignificantlyifthereandframecycledynamicallytoovercomethedrawbackofareasufficientnumberofidleslotsavailableforcooperativeitspreviousprotocol,USAP.However,USAP-MAspecifiesretransmission,eventhoughoverheadisintroduced.IndexTermscooperativeMACprotocol,wirelessnetworks,neitherhoworwhentochangetheframelengthnorhowtimedivisionmultipleaccess(TDMA),dynamicslotassignment.toselectaslotassignedtoanewnode.InASAP[10]andE-ASAP[11],whicharebasedontheUSAPconcept,theframelengthisdefinedasapowerof2.ItcanbechangedI.INTRODUCTIONdynamicallyaccordingtothetrafficrequirements.Recently,Cooperativecommunicationisapromisingtechniqueforwehaveproposedthefastdynamicslotassignmentscheme,enhancingtheperformanceofwirelessnetworks.WecanusecalledF-DSA,toreducetimeslotaccessdelayforanewlycooperativediversitytoattaincompletespatialdiversityamongarrivednodesinadhocnetworks[12].F-DSAsimplifiesthedistributedsingle-antennanodes.Thebasicideaofcooperativeslotassignmentprocessbyusingmini-slotstosharecontroldiversityisthatseveralsingle-antennanodescooperateinorderpacketforshortperiods.toprovidespatialdiversitybyformingadistributedmulti-Tothebestofourknowledge,cooperativeTDMAwithaantennasystem.Ontheotherhand,timedivisionmultipledynamicslotassignmentschemeanditsperformanceanalysisaccess(TDMA)canimproveslotutilizationbydynamicallyhasnotbeeninvestigated.Thus,onthebasisoftwopromisingreleasingownershipofunusedtimeslots,whicharereservedtechnologies,i.e.,cooperativecommunicationanddynamicbynodesbutaretemporarilynotbeingused,anditalsoslotassignment,weproposeacooperativeTDMAprotocolacquiresothertimeslotswhennecessary[1].Thus,aTDMAwithdynamicslotassignemtscheme.TheproposedTDMAen-systemwithadynamicslotassignmentschemecanachieveablesdynamicslotassignmentforcooperativeretransmissionhighefficiencyintermsoftime-slotusage,eventhoughincaseoferroneousreceptionsandthusprovidesrobustnessanadditionaloverheadforownershipchangemechanismistotheTDMAagainstwirelesschannelimpairments.Theintroduced.contributionofthisstudyistheproposalofasimpledynamicRecently,severalcooperativeMACprotocolshavebeencooperativeTDMAandthepresentationoftheanalyticalde-developedforTDMAsystems.ATDMA-basedMACpro-viationofthethroughputbyconsideringtheoverheadimpacttocolhasbeenproposedforcooperativecommunicationininRayleighfadingchannels.wirelessnetworks[2].Throughelaboratemini-slotdesign,theTherestofthispaperisorganizedasfollows.InSectionIITDMA-basedMACprotocolcanachievehighlysuccessfulandIII,wedescribesystemmodelandtheproposedprotocoltransmissionrates.However,theimpactofoverheadduetoindetail.InSectionIV,wederivethethroughputofthetheminislotswasnotelucidated.Meanwhile,aTDMA-basedconventionalTDMA,C-TDMA,andtheproposedTDMAcooperativeMACprotocol,calledC-TDMA[4],hasbeeninRayleighfadingchannels.InSectionV,weprovidethe978-1-4673-5742-5/13/$31.00©2013IEEE216ICOIN2013 Fig.1.TDMAMACframestructurefortheproposedTDMAprotocol.analyticalandsimulationresults.Finally,inSectionVI,weconcludethepaper.II.SYSTEMMODELANDASSUMPTIONWeconsiderdynamicTDMAslotassignmentprotocolsinasinglehopnetworkofNnodes,wheretransmissioniscarriedoutoveraRayleighfadingchanneltoasinglereceiverem-ployingamaximal-ratiocombiner(MRC).WehaveproposedTDMAframestructureusingminislotsforadhocnetworkFig.2.PackettransmissionprocedurefornodeiintheproposedTDMA.[12].AsshowninFig.1,theframeisperiodicallyrepeated(Misthenumberoftheslotinaframe)anddividedintotwoparts;aSignalingPeriod(SP)andaDatatransmittingPeriod(DP).SP,whichconsistsofminislots,isusedforexchangingalltheinformationneededIII.PROPOSEDCOOPERATIVETDMAtoperformtimeslotschedulingforcooperativeretransmission.ThereceiverofapackettransmittedineachtimeslotisInthissection,webrieflydescribeourproposedprotocol.determinedduringSP.DP,ontheotherhand,containstimeWhenasourcenodefailstotransmitapacketbecauseofslots,whicharereservedfordatatransmission.Eachtimeslotnoiseorfadingeffect,severalscenariosforneighboringnodesandminislotisexclusivelyallocatedtoanode.WeassumethatarepossibledependingonthereceptionoftheoriginalpacketinfromationfromtheminislotinSPandimmediatefeedbackanditscorrespondingnegativeacknowledgment(NACK).If(positiveornegativeacknowledgement)attheendofeachtimeaneighboringnodesuccessfullydecodestheoriginalpacketslotaretransmittedthroughanerror-freechannel.AreliableanditscorrespondingNACKduringitstimeslot,thenodelinkforsmallsizedpacketscouldbeachievedbyusingalow-willserveasacooperativenodeandwilltransmitthispacketratetransmissionwithappropriatequantizationschemes.Thetogetherwiththesourcenodeduringtheselectedtimeslotfordesignofahigh-qualitylinkandtheeffectofnoisypacketcooperativeretransmissioninthefollowingframe.arebeyondthescopeofthispaper.Inaddition,itisassumedWhentransmissionofapacketfails,notonlythesourcethatallnodesaresynchronizedandthatallpacketshaveequalnodebutalsothecooperativenodeswithnopacketstotransmitlength.havetheresponsibilityofsuggestingatimeslotforcooperativeAk-elementvirtualantennaarrayisformedbyconsideringretransmissionofthefailedpacketduringitsminislot.Then,k−1cooperativenodesplusthesourcenode(e.g.,intheformthecooperativenodessuggestionhasahigherprioritythanofmultiple-inputsingle-output(MISO)).Assumingabinarythatofthesourcenode.Thisimpliesthatthesourcenodedoesphase-shiftkeying(BPSK)modulationscheme,theaveragebitnotneedtosuggestitstimeslotforcooperativeretransmissionerrorrate(BER)underRayleighfadingforanMRCreceiverifacooperativenodessuggestionhasalreadybeenannounced.withk-branchdiversityisgivenas[3]:Onthecontrary,acooperativenodeshouldannounceitsπsuggestionevenifasourcenodehasalreadyannouncedits12ζ¯P¯(ζ,k¯)=(1+)−kdφ,(1)suggestion.Meanwhile,multipleneighboringnodescanbebπsinφ20cooperativenodesformultiplefailedpacketsandthesugges-whereζ¯referstotheaverageSNRperlink.NotethatthetionsareannouncedinorderduringtheSP.Thus,incasetheaverageBERdoesnotdependonthemodulationscheme,andtimeslotforaspecificfailedpacketisalreadysuggestedbyaanymodulationschemecanbeusedinsteadofBPSK[5].cooperativenode,othernodessuggestforotherfailedpackets.P(k)=(1−P¯(k))µ,andthus,theprobabilityofpacketInotherwords,itenablesmultipletimeslotstobescheduledsberrorisPe(k)=1−Ps(k).WeassumethattheSNRcanbeformultiplepacketsduringasingleSP.Meanwhile,incaseestimatedatthereceiverforeachlinkandthatitremainsstaticnocooperativenodeprovidesasuggestionforafailedpacket,foratimeslot.Synchronizationamongthetransmittingnodesthepacketwillbecooperativelyretransmittedinthesourcecanbeachievedviatechniquesmentionedin[6],andincaseofnodestimeslotiftherearecooperativenodes;otherwise,itimperfectsynchronization,oneofthemethodsreviewedin[7]isretransmittedbythesourcenodealone.canbeemployedsothatdiversitygaincanstillbeachieved.Sinceneighboringnodesretransmitthesamepacketwitha217 A.C-TDMAWebrieflyintroducetheanalyticalmodelforC-TDMAinwhichcooperativeretransmissionoccursonlyinthesourcenodestimeslot.Pleasereferto[4]forthedetail.LetQr(t)denotetheprobabilitythattnodesbecomecooperativenodesforasourcenodewhosepackettransmissionfailed.ThatisN−1tN−t−1Qr(t)=[Ps(1)][1−Ps(1)].(2)tIn[4],Pnthhasbeenusedtorepresenttheprobabilityofretransmissionbythenthtime(n=0,1,2,...)foraspecificpacketbecauseofprevioustransmissionfailures.Here,retrans-Fig.3.OperationexampleoftheproposedTDMAprotocol.thmissionbythe0timeimpliesthatthepacketissuccessfullytransmittedwithnoretransmission.Pnthcanberepresentedbydifferentfadingchannel,itresultsindiversitygain.Moreover,anotherpacketofthesourcenodecanbetransmittedduringtheexclusivelyallocatedtimeslot,whilethefailedpacketisp0thn=0cooperativelyretransmittedduringacooperativenodestimep1thPe(1)n=1slot.Thus,thissimplemechanismimprovesthethroughputofN−1n−1(3)pnthPe(1){t=1Qr(t)[Pe(k+1)]thenodes.N−1n−1Fig.2showthepackettransmissionprocedurefornode+(1−t=1Qr(t))[Pe(1)]}n>1.∞iintheproposedTDMA.EachnodestoresafailedpacketSincen=0Pnth=1,thespecificvalueofP0thcanbecalcu-untilACKforthepacketisreceievedorthepacketexceedthelatedbytime-to-livevalue,whichdependsontheapplicatoins.Nodeitransmitsitsownpacketinthereservedslot.IfNACKisN−1P(k+1)P1+P(1)+P(1)Q(t)e+receivedattheendoftheslot,thepacketisplacedonthe0th=eet=1r1−Pe(k+1)−1(4)listforafailedpacket.Innon-reservedslot,ontheother(1−N−1Q(t))Pe(1).t=1r1−Pe(1)hand,nodeitransmitsafailedpacketwhenthecurrentslotisselectedforcooperativeretransmissionofafailedpacketThus,theaveragetransmissionerrorprobabilitycanbeob-∞ththatarestoredinnodei.IftheslotisnotselectedforafailedtainedbyP¯e=n=0PnthPr(Error|n).Thatispacket,nodeioverhearscommunicationamongneighborstoP¯=P(1)1+N−1Q(t)Pe(k+1)updatefailedpacketinformation.e0thPet=1r1−Pe(k+1)(5)Fig.3illustratesasimpleoperationexampleoftheproposedN−1Pe(1)+(1−t=1Qr(t))1−Pe(1).protocol.Eachnodehasanexclusivelyassignedminislotandtimeslot.(x)ineachslotdenotesthatthenodexistheFinally,thethroughputoftheC-TDMAsystemcanbegivenownerofthecorrespondingslot.Weassumethattherearebyfournodesinthenetworkandthatpackettransmission(packetTC−TDMA=1−P¯e.(6)1)fromnodeAtonodeDhasfailedandnodeBandCarecooperativenodesthathavenopackettotransmit.Initially,B.ProposedTDMAnodeAsuggestsitstimeslotforcooperativeretransmissionFortheproposedTDMA,wedefinethethroughputasduringitsminislotinSP.NotethatnodeAisthesourceT(β),whereβisanoverheadfactorthatistheratioofSPnodeforthefailedpacket.Thus,bytheruleoftheproposedlengthtoframelength.UnlikeinC-TDMA,idleslotsintheTDMA,nodeBalsosuggestsitstimeslot.NodeCdoesnotproposedTDMAcanbeusedforcooperativeretransmissionneedtodosobecausenodeBhasalreadysuggesteditstimeoffailedpackets,andthesourcenodecantransmitanotherslotforthesamepacket.Then,nodeAcantransmitanewpacketduringitsexclusivelyallocatedtimeslotinthesamepacket(packet2)duringitstimeslotandthefailedpacketframe.Thisimpliesthattheoriginalnodecanachievebetter(packet1)willbecooperativelyretransmittedbynodeA,B,throughputbyexploitingtheidleslots.Thus,thethroughputandCduringnodeBstimeslot.oftheproposedTDMAsystemwillbemaximizedifallretransmissionsoccurduringidletimeslots.IV.THROUGHPUTANALYSISOFTHEPROPOSEDTDMAWedonotconsidertheimpactofSPslengthonthethroughput,i.e.,SPslengthiszero,butwewillanalyzeInthissection,wedevelopanalyticalmodelsforthepro-thethroughputofproposedTDMAconsideringtheimpactposedTDMAintermsofthethroughputinRayleighfadingofSPslengthlater.Whenapackettransmissionfails,thechannels.probabilitythatatleastoneormorenodesbecomecooperative218 is(1−Qr(0)),fromEq.(2).Thus,theaverageerrorprobabilityofcooperativeretransmissionisgivenbyN−1P¯e,r=Qr(k)Pe(k+1).(7)k=1Thus,thethroughputofproposedTDMAwillbemaximizedifallcooperativeretransmissionsoccurduringidletimeslots;themaximizedthroughputcanbeexpressedasTmax(0)prop(8)=Ps(1)+Pe(1)(1−Qr(0))(1−P¯e,r)Thefirsttermontheright-handsideofEq.(8)representsthethroughputofTDMA,andthesecondtermrepresentstheFig.4.Throughputsobtainedbyvaryingγ(SNR=25dB,N=10).throughputgainbyexploitingtheidleslotsforcooperativeretransmission.A.ImpactofchanneloccupancyratioHowever,inrealsystems,somepacketsarecooperativelyretransmittedduringthesourcenodestimeslotincasealltheFig.4illustratestheplotofthethroughputperformancecooperativenodesforthefailedpacketarenotidle.Thus,theoftheproposedTDMA,C-TDMA,andTDMAobtainedprobabilityαthatafailedpacketisretransmittedcooperativelythroughtheoreticalanalysisandsimulationbyvaryingγ.Itduringthesourcenodestimeslotcanbegivenasshowsthattheanalyticalandsimulationresultsarealmostthesame.ThelargeγimpliesthattheprobabilitythatthereN−1aretimeslotsavailableforcooperativeretransmission,i.e.,α=Q(k)γk,(9)ridleslots,islow.ItisclearlyseenthattheTDMAsystemk=1suffersfromchannelerrors,andtheC-TDMAandproposedTDMAsystemscaneffectivelyimprovethethroughput.γ=whereγisthechanneloccupancyratioofthenumberofbusy1impliesthatthereisnoidleslot,andiftheoverheadeffecttimeslotstothenumberoftotaltimeslotsinaframe,anditisnegligibleintheproposedTDMAsystem,i.e.,βisclosecanbeconsideredastheprobabilitythatanodeisbusy.tozero,thesystembecomesaC-TDMAsystem,whichhasIfthefailedpacketisalwaysretransmittedcooperativelynocooperativediversityduringidleslots.Itisobservedthatduringthesourcenodestimeslot,theuserthroughputofthethethroughputofTDMAcanbeimproveddrasticallybyaproposedTDMAsystemisidenticaltothatofaC-TDMAcooperativeretransmissionschemeusingidleslots.Thisissystem,asgiveninEq.(6).ThethroughputofproposedbecausewhenthetransmissionofapacketfailsinthepreviousTDMAsystem,usingEqs.(6),(8)and(9),withoutconsideringframe,notonlythefailedpacketbutalsoanotherpacketinthetheimpactofSPisexpressedassourcenodesbuffercanbetransmittedinthefollowingframe.InspiteofSPdegradingthethroughput,thethroughputoftheTprop(0)(10)proposedTDMAissuperiortothatofC-TDMAoverawide=(1−α)Tmax(0)+αT.propC−TDMArangeofγ.Finally,thethroughputwithoverheadfactorcanbecalculatedB.ImpactofSNRbymultiplyingtheEq.(10)with1/(1+β)asfollowsFig.5illustratestheplotofthethroughputsfordifferentTprop(0)SNR,whereγ=0.7andN=10.Forallsystems,thethrough-Tprop(β)=.(11)puthasatendencytoincreasewiththeSNR.Forrelatively(1+β)lowSNR(whenlessthanabout25dB),inspiteofthroughputV.ANALYTICALANDSIMULATIONRESULTSdegradationcausedbyoverheadimpact,thethroughputoftheproposedTDMAsystemisincreaseddramaticallywithInthissection,wecomparethethroughputoftheproposedincreaseofSNRanditishigherthanthatofothersystems.TDMAsystemwiththatoftheTDMAandC-TDMAsystemsThisisbecausethepackettransmissionfailurecausedbyainRayleighfadingchannels.Inoursimulationandanalyticaldeepfadingchannelcanbeeffectivelytreatedwithcooperativeevaluations,theSNRisassumedtobe25dB,thepacketlengthretransmissioninidleslots.Onthecontrary,incaseofhighis1024bits,andthefadingisassumedtobeconstantwithinSNR(whengreaterthanabout30dB),itremainsstableeveneachtimeslot(blockfading).Inaddition,weassumethatNthoughSNRincreases.Thisisbecausethattheprobabilityis10.FortheproposedTDMA,anoverheadfactorβissettoofsuccessfultransmissionbecomessohighthatcooperative0.01,0.1,or0.2dependingonthenetworkfeatures.retransmissionisnotusedfrequently.Thus,thethroughputof219 VI.CONCLUSIONANDFUTUREWORKSInthispaper,weproposedasimplecooperativeTDMApro-tocolwithdynamicslotassignmentschemeandpresenteditsanalyticalthroughputmodelunderRayleighfadingchannels.Wederivedthethroughputbyconsideringanoverheadimpactcausedbythedynamicschedulingforcooperativeretransmis-sion.Furthermore,thetheoreticalanalysiswasvalidatedbythesimulations.WecomparedthethroughputsoftheproposedTDMAwiththeC-TDMAandTDMA.Thetheoreticalandsimulationanalysesshowedthatbyexploitingtheneighboringnodesidletimeslotsandthediversitytoovercomechannelimpairments,thethroughputoftheproposedTDMAcanbesignificantlyimproved.OurproposedTDMAisparticularlyeffectiveunderalowchanneloccupancyratioindenselyFig.5.ThroughputsobtainedbyvaryingSNR(γ=0.7,N=10).deployednetworkssufferingfromimperfectchannels.TheproposedTDMAconsideronlysinglehopnetworksinwhicheachnodecandirectlycommunicatewithothernodesthroughasharedcommunicationchannelsothatwewillextendthisprotocoltomulti-hopadhocnetworks.ACKNOWLEDGMENTThisresearchwassupportedbytheMKE(TheMinistryofKnowledgeEconomy),Korea,undertheITRC(InformationTechnologyResearchCenter)supportprogramsupervisedbytheNIPA(NationalITIndustryPromotionAgency(NIPA-2012-(H0301-12-2003)).REFERENCES[1]SunilKumar,Vineet.S.RaghavanandJingDeng,MediumAccessControlprotocolsforadhocwirelessnetworks:Asurvey,ElsevierAdHocNetworks,vol.4,issue3,pp.326-358,2006.[2]HongzhiJiaoandFrankY.Li,Amini-slot-basedcooperativeMACprotocolforwirelessmeshnetworks,Proc.IEEEGlobecomWorkshops,Fig.6.ThroughputsobtainedbyvaryingN(γ=0.7,SNR=25dB).2010,pp.89-93.[3]A.J.Goldsmith,WirelessCommunications,1sted.NewYork:CambridgeUniversityPress,2005.[4]ZhuoYang,Yu-DongYao,XiaochenLi,andDiZheng,ATDMA-BasedtheproposedTDMAsystemislowerthanthatofothersystemsMACProtocolwithCooperativeDiversity,IEEEComm.Letters,vol.14,becauseoftheoverheadimpact,i.e.,theSPduration.No.6,pp.542-544,2010.[5]M.S.Gokturk,O.Ercetin,andO.Gurbuz,ThroughputanalysisofALOHAwithcooperativediversity,IEEEComm.Letters,vol.12,No.6,pp.468-470,June2008.C.Impactofthenumberofnodes[6]D.L.Mills,Internettimesynchronization:thenetworktimeprotocol,IEEETrans.Commun.,vol.39,no.10,pp.1482-1493,Oct.1991.Fig.6showstheplotofthethroughputobtainedbyvarying[7]G.Jakllari,S.V.Krishnamurthy,M.Faloutsos,P.V.Krishnamurthy,andN,whereγ=0.7andaverageSNR=25dB.WeincreasedO.Ercetin,Across-layerframeworkforexploitingvirtualMISOlinksinmobileadhocnetworks,IEEETrans.MobileComput.,vol.6,no.6,Nupto25.IncaseofN=1,cooperativeretransmissionispp.579-594,June2007.impossibleasthereisnoneighbornode.Thus,thethroughputs[8]C.D.Young,USAP:AunifyingdynamicdistributedmultichannelofC-TDMAandproposedTDMAwithverysmallβareTDMAslotassignmentprotocol,IEEEMILCOM,pp.235-239,Oct.1996.similartothatofTDMA.Itisclearlyseenthatthethroughput[9]C.D.Young,USAPmultipleaccess:dynamicresourceallocationforofC-TDMAandproposedTDMAimproveasthenumbermobilemultihopmultichannelwirelessnetworking,IEEEMILCOM,pp.ofusersgrows.However,incaseoflargenumberofnodes271-275,Nov.1999.[10]A.Kanzaki,T.Uemukai,T.HaraandS.Nishio,DynmicTDMAslot(whengreaterthanabout15),thethroughputofTDMAsystemassignmentinadhocnetworks,17thIEEEAINA,pp.330-335,Marchremainsalmoststeadyregardlessofthenumberofusers.It2003.impliesthatthenumberofneighbornodesaboveacertainlevel[11]A.Kanzaki,T.HaraandS.Nishio,AnadaptiveTDMAslotassignmentprotocolinadhocsensornetworks,ACMSymposiumonAppliedisnotrequiredtoimprovetheperformance.AsitisobservedComputing,pp.1160-1165,March2005.fromthefigure,ifthenumberofneighbornodesisabovea[12]J.K.Lee,K.M.Lee,andJ.S.Lim,DistributedDynamicSlotcertainlevel(whengreaterthanabout5),theproposedTDMAAssignmentSchemeforFastBroadcastTransmissioninTacticalAdHocNetworks,Proc.IEEEMILCOM,Oct.2012.systemhasabetterthroughputthanaC-TDMAsystem,eventhoughadditionaloverheadisintroduced.220