send-传送资料前传送者会先要求接收者传送RTS

ANovelMediumAccessControl(MAC)ProtocolforAdHocNetworkAuthors:Qingchun

RenandWeiGuoSource:AINAProceedingsofthe17thInternationalConferenceonAdvancedInformationNetworkingandApplicationspp.521Presenter:

Chunh-ChihLoDate:

24-01-20071OutlineIntroductionHiddenandExposedTerminalProblemCSMAVSNovelMACprotocolBRODpacketFormatofBRODPacketandNeighborTableMainstepsofalgorithmSolve

HiddenandExposedTerminalProblemSimulationParametersandResultsConclusion2IntroductionAdHocNetworkTemporarydynamicenvironmentDonotneedAPbasestation,Multi-hopwirelesslinksUsefulinmilitaryandemergencyrescue.Useincommercialapplicationsandforcommunicationserviceswithoutthepresenceofafixedinfrastructure.3HiddenterminalsproblemAsendstoB,CcannotreceiveACwantstosendtoB,Csensesa“free”mediumcollisionatB,AcannotreceivethecollisionAis“hidden”fromC

AandCwantto

sendtoBAsendsRTSfirstCwaitsafterreceiving

CTSfromBABCRTSCTSCTSCBA4ExposedterminalsproblemBsendstoA,Cwantstosendtoanotherterminal(notAorB)Csensescarrier,findsmediuminuseandhastowaitAisoutsidetheradiorangeofC,thereforewaitingisnotnecessaryCis“exposed”toBBwantstosendtoA,C

toanotherterminalnowCdoesnothave

towait,asitcannot

receiveCTSfromACBAABCRTSCTSRTS5CSMAVSNovelMACprotocolCSMAProtocolListenstotransmittingstatusandsendwhennooneistransmittingandmaybeinterferencebyothernodes.ReducetheefficiencyofsystemperformanceDecreasetheutilizationofchannelresource.NovelMACprotocolReducetheeffectonthesystem.Increasetheutilizationofchannelresource.6BRODpacketBeforesend/receivepackets,sendaBRODpacket.Broadcastsourceanddestinationofthedatapacket,whichisreadytotransmit.Othernodescandeterminetherighttimetotransmitpacketwithoutcollision.Othernodescanknowwhichnodeswillusethechannelduringwhichperiod.7BRODpacket(cont.)MakeuseoftransmissionofwirelesscharacteristicAllnodesthatisinrangeofsender,canreceivesignalevenit’snotthedestinationofthepacketbutwilldiscardit,notrelayit.LifetimeofBRODpacketisonlyonehopLimittheoverhead,highthroughputandlowdelay.Nointerruptbetweennodeswhichisnotneighborofthesenderanditisunnecessarytogetthispacket.

8FormatofBRODPacketandNeighborTableFormatofBRODPacketWhenreadytosenddatapacket,SUBTYPEwillbe1.Whennodeisbusy,SUBTYPEwillbe2.ContentsofNeighborTableEverynodehaveneighbortableandrefreshesaccordingtotheBRODpacket.9MainstepsofalgorithmBeforesenddatapacket,checkneighbortabletoseeifitisneighborandifitisbusyTransmittingTotalsizeofpacket/Transmissionbandwidth1IfitisneighborIfitisnotneighborthendon’tchangeanything2Ifitisbusy10Mainstepsofalgorithm(cont.)BORDpacket(SUBTYPE=1),GetsinformationaboutSOURCEID,DESTINATIONIDandDURATION.SourceDestinationTRANSMITTINGRECEIVINGelsedon’tdoanythingBORDpacket(SUBTYPE=2),refreshtherelateinformationintheneighbortableRECEIVINGTRANSMITTINGIfthesourceanddestinationisitsneighborthen11Mainstepsofalgorithm(cont.)1IfitisdestinationsendBROD(Subtype=2)packet(SamefieldsastheBRODpacket(SUBTYPE=1)exceptfortheSUBTYPEfield)DURATIONsurpassthelifetime,thevaluesinitsneighbortablewillbereset(STATUS=IDLE,DURATION=0.0).Beforenodewanttosentoutdatapacket,nodemustcheckifthereisnodereceiving,ifyesthendelayitstransmission;elsedoitastheplanSourceDestination20.0IDLESourcesendBROD(Subtype=1)packet12SolvehiddenterminalproblemsAandCwantto

sendtoBAsendsBRODfirstCdelaytransmissionBRODStatus=TransmittingStatus=Receiving13SolveexposedterminalproblemsBsendtoA,CtoanotherterminalnowCdoesnothave

towait,CwillcheckdestinationsneighbortabletoseeifitisitsneighborStatus=TransmittingStatus=Receiving14SimulationParametersMeasurethethroughput,mean-delay,probabilityofsuccessfultransmissionandmean-attemptofthenetwork.Simulationsweredoneindifferentnumberofnodeanddistance.15Throughput,mean-delay,mean-attemptandprobabilityofsuccessfultransmissionareimprovedatthesamecondition,inwhichtheprobabilityforcollisionissame.Whenthecommunicationdistancerangeislongerthan250orshorterthan150meters,thehiddenandexposedterminalproblemarenotobvious.Theperformancedifferentmuchwhendistanceisbetween150and250metersinwhichthereareseverehiddenandexposedterminalproblem.SimulationResults16ConclusionFromthesimulationresults,theperformancesof