Primary channel assignment based MAC(PCAM)-multich

PrimaryChannelAssignmentbasedMAC(PCAM)–AMulti-ChannelMACProtocolforMulti-HopWirelessNetworksJayaShankarPathmasuntharam1,21NetworkingDepartment,CommunicationsandDeviceDivision,InstituteforInfocommResearch,21HengMuiKengTerrace,[e-mail]2,AnilKumarGupta22ComputerCommunicationsDivision,SchoolofComputerEngineering,NanyangTechnologicalUniversity,Singapore{asadas,asgupta}@ntu.edu.sgAbstract—SomewirelessMACprotocolssuchasIEEE802.11werenotdesignedtocapitalizeontheavailablemultiplechannelsinanefficientmanner.Inthispaper,weproposeanovelmulti-channelmediumaccesscontrolprotocolforwirelessnetworkswhichwetermas“PrimaryChannelAssignmentbasedMAC”.Theprotocolisbasedontheuseofprimarychannelassignment,whichisusedbyothernodestofindthecorrespondingnode.Wealsointroduceamethodtoreducethehiddenterminalproblemencounteredinmulti-channeldesignsbyproposingamodifiedtransmissionrangethreshold.Theschemeeliminatestheneedforaseparatededicatedcontrolchannelortimeslotthatisusuallypronetosaturationwhenthetrafficincreases.Theproposedschemealsoaddressesthebroadcastmessagesprobleminmulti-channeldesign.TheschemeisbasedonIEEE802.11DCFprotocol.Theperformanceoftheproposedprotocoliscomparedtotwoothermulti-channelschemes.Inanad-hocnetwork,theprotocolout-performstheotherprotocolsbyupto140%.Keywords-component;Multi-channelMAC,Ad-HocNetworks,WirelessLAN.I.INTRODUCTIONStudieshaveshownthatwirelessnetworksprovidedismalcapacityinthepresenceofmanynodesinagivenarea.GuptaandKumar[12]haveshownthattheper-nodecapacityinan-noderandomad-hocnetworkisgivenbyΩ(1/nnlog).Thecapacityofwirelessad-hocnetworkshasalsobeenstudiedforsimplechainandlatticesetups,whichalsoconfirmthisobservation[11].Forachainsetup,Lietal.showedthatthecapacityof802.11reachesabout1/7theeffectivebandwidthofthechannel.Intherecentpast,researchhasbeencarriedouttoimprovethethroughputofwirelessnetworks,andvariousapproacheshavebeenproposed.Spatialdirectivityintheantennasorbeam-formingisonemethodusedtoincreasetheconcurrencyandthusincreasethecapacityofthewirelessnetwork.Otherschemesincludetheuseofpropertransmissionschedulingwithinawirelessneighborhood.InthispaperweproposeanewMACprotocolschemeknownasthe“PrimaryChannelAssignmentbasedMAC”(PCAM)forincreasingtheper-nodecapacityandoverallthroughputofsystemthroughtheuseofmultiplechannels.Althoughanumberofschemesformulti-channelMACexist,mostofthemethodsproposedtilldaterequireeitherafrequencyortimeseparateddedicatedcontrolchannelwhichsuffersfromsaturationatheavyloads.Incontrast,thePCAMschemedoesnotrequireanydedicatedcontrolchannelorcomplexsynchronization.Ithoweverrequires3half-duplextransceiverspernode,whichcanbereducedto2ifspecialtransceiversareused.Inthispaper,wecomparetheperformanceofPCAMprotocolwithtwootherprotocols,DynamicChannelAssignment(DCA)[4]andMulti-ChannelMAC(MMAC)[6].II.PRELIMINARIESA.HiddenterminalproblemsFigure1.HiddenterminalproblemIndesigningamulti-channelscheme,thehiddenterminalproblemhastobeaddressedcarefully.Wuetal[4]givesanexampleofhowhiddenterminalissuesarisewhenasingle-channel802.11designisadaptedtoamulti-channelscenario.AnotherexampleproblemthatappliestodesignsthatemploychannelswitchingwithoutpriorreservationisdepictedinFigure1.NodeAiscommunicatingtonodeBinacommonchannel.NodeCswitchestothischannelaroundtimeT1whereitmissestheCTSsentoutbyB.IfnodeC,whichisahiddenterminal,proceedstotransmittosomeothernodeaftersensinganidlechannel,thesignalcouldcollideatB.RTSCTSDATAACKABCtimetimetimeT1ABCB’sSensingRangeB’sTransmissionRangeWCNC2004/IEEECommunicationsSociety11100-7803-8344-3/04/$20.00©2004IEEEB.BusyReceiverAnotherissuethatneedstobetakenintoconsiderationistheavailabilityofthereceiverwhenatransmitterswitchestopresumedreceiver’schannel.Inadesignwherethereceiveristunedtoanotherchannel,whilethisswitchingoccurs,itwillnotbeabletolistentobroadcastorRTSsignals.C.BroadcastmessagesAd-hocnetworkprotocolsaredependentonthebroadcastnatureofwirelessmediumtooperateeffectively.Routediscovery,routemaintenance,addressresolutionaresomeofthemessagesthatdependonbroadcastmessages.Duetomobility,congestionandunpredictablewirelesschannelinad-hocnetworks,nodesusuallyloseconnectivityandhavetoupdatetheirroutesfrequently.Indesigningamulti-channelscheme,wehavetotakeintoconsiderationtheneedforbroadcastmessages.Itisinefficientforamulti-channelschemetohavenodesswitchtoanotherchannelandmissoutonthebroadcastmessages.Inschemesthatuseaseparatededicatedcontrolchannel,nodeswillberequiredtousethischanneltobroadcasttoothers.Weproposeamulti-channelMACprotocolthataddressesalltheseproblems.III.RELATEDWORKTherehavebeenmanyresearcheffortsonmulti-channelMACprotocolsforad-hocnetworksinthepastfewyearscoveringcontentionbasedMACschemes[1-8].Nasipurietal.[1]proposedaschemethatusescarrier-sensingmechanismtoperformchannelassignmentasopposedtootherschemesthatusebroadcastschedulingoradditionalmessaging.Jainetal.[2]proposedaCSMA-basedMACcalledreceiver-basedchannelselection(RBCS)thatusesshortreservationpacketsoveradedicatedcontrolchannel.OnecontrolchannelandNdatachanne