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基于对数函数的AdHoc网络MAC退避算法.docx

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基于对数函数的AdHoc网络MAC退避算法 Introduction AdHocnetworksaretemporarynetworksthatcanbecreatedwithouttheneedforapre-existinginfrastructureorcentraladministration.Thesenetworksarehighlymobile,dynamic,andself-organizing.Insuchnetworks,theMediumAccessControl(MAC)layerplaysanimportantroleinmanagingaccesstothesharedchannel.OneofthemajorchallengesinAdHocnetworksistoprovideefficientandfairaccesstothenetworkresourceswhileminimizingcollisionsandmaximizingthethroughput.Inthispaper,weproposeaMACprotocolbasedonthelogarithmicfunctionforAdHocnetworks. Background TheIEEE802.11standardprovidesasetofMACprotocolsforwirelessnetworks.However,theseprotocolsarenotsuitableforAdHocnetworksduetotheircentralizednatureanddependenceonaninfrastructure.Hence,severaldistributedMACprotocolshavebeenproposedforAdHocnetworks,suchasCarrierSenseMultipleAccesswithCollisionAvoidance(CSMA/CA)andDistributedCoordinationFunction(DCF). Theseprotocolsfollowacontention-basedapproach,wherenodescompeteforaccesstothesharedmedium.However,thecontentionprocesscanleadtocollisions,whichdecreasethenetworkefficiency.Moreover,traditionalMACprotocolsdonotconsiderthefairnessbetweendifferentnodesthathavedifferenttransmissionrequirements.Hence,thereisaneedforanewMACprotocolthatcanprovideefficientandfairaccesstothesharedchannel. ProposedMACProtocol TheproposedMACprotocolisbasedonthelogarithmicfunction,wherenodesselecttheirbackoffcounterbasedontheprevioustransmissiontime.Inthismethod,thebackoffcounterforanodeisdefinedas: backoffcounter=c*log10(t+1) wherecisaconstantthatdeterminestherangeofbackoffcountervalues,tistheprevioustransmissiontime,andlog10isthelogarithmicfunctionwithbase10. Therationalebehindusingthelogarithmicfunctionisthatitprovidesaproportionalincreaseinthebackoffcounterastheprevioustransmissiontimeincreases.Thisensuresthatnodesthattransmitfrequentlywillhaveahigherbackoffcounterandwillhavealowerprobabilityofaccessingthechannelcomparedtonodesthattransmitlessfrequently.Hence,theproposedprotocoloffersfairnessbetweendifferentnode