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多小区OFDMA系统中基于POMDP的干扰协调.docx

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多小区OFDMA系统中基于POMDP的干扰协调 1.Introduction MultiplesmallcellOFDMAsystemsarebecomingincreasinglypopularthesedays,duetotheirabilitytodealwiththeincreasingdemandforhigh-speedwirelessdataservices.However,oneofthebiggestchallengesassociatedwiththistechnologyistheissueofinterferencethatarisesduetothecoexistenceofmultiplesmallcellsinthesamearea.Therefore,efficientinterferencecoordinationmechanismsarenecessarytoensurethatusersreceivequalityservice.ThispaperexplorestheuseofPartiallyObservableMarkovDecisionProcess(POMDP)tocoordinateinterferenceinmultiplesmallcellOFDMAsystems. 2.Background OFDMA(OrthogonalFrequencyDivisionMultipleAccess)isamultipleaccessschemethatdividesthespectrumintomultipleorthogonalsubcarriers,whereeachsubcarriercanbeassignedtoadifferentuser.InOFDMAsystems,interferenceiscausedwhenmultipleusersareassignedtothesamesubcarrier.Interferencecoordinationisnecessarytoensurethateachuserreceivesahigh-qualitysignal. 3.ExistingInterferenceCoordinationTechniques SeveraltechniqueshavebeenproposedintheliteratureforinterferencecoordinationinOFDMAsystems.Onetechniqueistoallocatesubcarrierstousersinawaythatminimizesinterference.Anothertechniqueistoadjustthetransmitpowerofeachusertolimitinterference.However,thesetechniquesareinefficientinmultiplesmallcellOFDMAsystemswheretherearenumeroususers. 4.POMDPforInterferenceCoordination POMDPisadecision-makingframeworkthatusesaprobabilisticmodeltorepresenttheuncertaintyassociatedwithasystem.Itisusefulinsituationswherethestateofasystemisnotdirectlyobservable.InPOMDP,actionsaretakenbasedonthebeliefofthesystemstate. InanOFDMAsystem,theinterferencecanbemodeledusingaPOMDPframeworkbyconsideringfactorssuchasthenumberofactiveusersinasmallcell,thesignalstrengthofeachuser,andtheamountofinterferenceexperiencedbyeachuser.Thestateofthesystemismodeledbasedonthesefactors,andtheactionsaretakenbasedonthebeliefofthesystemstate. 5.AdvantagesofPOMDPforInterferenceCoordination TheuseofPOMDPforinterferencecoordinationinmultiplesmallcellOFDMAsystemshasseverala