NeXt generation dynamic spectrum access cognitive

NeXtgeneration/dynamicspectrumaccess/cognitiveradiowirelessnetworks:AsurveyIanF.Akyildiz,Won-YeolLee,MehmetC.Vuran*,ShantidevMohantyBroadbandandWirelessNetworkingLaboratory,SchoolofElectricalandComputerEngineering,GeorgiaInstituteofTechnology,Atlanta,GA30332,UnitedStatesReceived2January2006;accepted2May2006Availableonline17May2006ResponsibleEditor:I.F.AkyildizAbstractToday’swirelessnetworksarecharacterizedbyafixedspectrumassignmentpolicy.However,alargeportionoftheassignedspectrumisusedsporadicallyandgeographicalvariationsintheutilizationofassignedspectrumrangesfrom15%to85%withahighvarianceintime.Thelimitedavailablespectrumandtheinefficiencyinthespectrumusageneces-sitateanewcommunicationparadigmtoexploittheexistingwirelessspectrumopportunistically.ThisnewnetworkingparadigmisreferredtoasNeXtGeneration(xG)NetworksaswellasDynamicSpectrumAccess(DSA)andcognitiveradionetworks.ThetermxGnetworksisusedthroughoutthepaper.Thenovelfunctionalitiesandcurrentresearchchal-lengesofthexGnetworksareexplainedindetail.Morespecifically,abriefoverviewofthecognitiveradiotechnologyisprovidedandthexGnetworkarchitectureisintroduced.Moreover,thexGnetworkfunctionssuchasspectrummanage-ment,spectrummobilityandspectrumsharingareexplainedindetail.Theinfluenceofthesefunctionsontheperformanceoftheupperlayerprotocolssuchasroutingandtransportareinvestigatedandopenresearchissuesintheseareasarealsooutlined.Finally,thecross-layerdesignchallengesinxGnetworksarediscussed.2006ElsevierB.V.Allrightsreserved.Keywords:Nextgenerationnetworks;Dynamicspectrumaccessnetworks;Cognitiveradionetworks;Spectrumsensing;Spectrummanagement;Spectrummobility;Spectrumsharing1.IntroductionToday’swirelessnetworksareregulatedbyafixedspectrumassignmentpolicy,i.e.thespectrumisregulatedbygovernmentalagenciesandisassignedtolicenseholdersorservicesonalongtermbasisforlargegeographicalregions.Inaddition,alargeportionoftheassignedspectrumisusedspo-radicallyasillustratedinFig.1,wherethesignalstrengthdistributionoveralargeportionofthewirelessspectrumisshown.Thespectrumusageisconcentratedoncertainportionsofthespectrumwhileasignificantamountofthespectrumremainsunutilized.AccordingtoFederalCommunications1389-1286/$-seefrontmatter2006ElsevierB.V.Allrightsreserved.doi:10.1016/j.comnet.2006.05.001*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddresses:[e-mail](I.F.Akyildiz),[e-mail](W.-Y.Lee),[e-mail](M.C.Vuran),[e-mail](S.Mohanty).ComputerNetworks50(2006)2127–2159(FCC)[20],temporalandgeographicalvariationsintheutilizationoftheassignedspectrumrangefrom15%to85%.Althoughthefixedspec-trumassignmentpolicygenerallyservedwellinthepast,thereisadramaticincreaseintheaccesstothelimitedspectrumformobileservicesintherecentyears.Thisincreaseisstrainingtheeffective-nessofthetraditionalspectrumpolicies.Thelimitedavailablespectrumandtheinefficiencyinthespectrumusagenecessitateanewcommuni-cationparadigmtoexploittheexistingwirelessspec-trumopportunistically[3].Dynamicspectrumaccessisproposedtosolvethesecurrentspectrumineffi-ciencyproblems.DARPAsapproachonDynamicSpectrumAccessnetwork,theso-calledNeXtGener-ation(xG)programaimstoimplementthepolicybasedintelligentradiosknownascognitiveradios[67,68].NeXtGeneration(xG)communicationnet-works,alsoknownasDynamicSpectrumAccessNetworks(DSANs)aswellascognitiveradionet-works,willprovidehighbandwidthtomobileusersviaheterogeneouswirelessarchitecturesanddynamicspectrumaccesstechniques.Theinefficientusageoftheexistingspectrumcanbeimprovedthroughopportunisticaccesstothelicensedbandswithoutinterferingwiththeexistingusers.xGnet-works,however,imposeseveralresearchchallengesduetothebroadrangeofavailablespectrumaswellasdiverseQuality-of-Service(QoS)requirementsofapplications.Theseheterogeneitiesmustbecap-turedandhandleddynamicallyasmobileterminalsroambetweenwirelessarchitecturesandalongtheavailablespectrumpool.ThekeyenablingtechnologyofxGnetworksisthecognitiveradio.Cognitiveradiotechniquespro-videthecapabilitytouseorsharethespectruminanopportunisticmanner.Dynamicspectrumaccesstechniquesallowthecognitiveradiotooperateinthebestavailablechannel.Morespecifically,thecog-nitiveradiotechnologywillenabletheusersto(1)determinewhichportionsofthespectrumisavail-ableanddetectthepresenceoflicenseduserswhenauseroperatesinalicensedband(spectrumsens-ing),(2)selectthebestavailablechannel(spectrummanagement),(3)coordinateaccesstothischannelwithotherusers(spectrumsharing),and(4)vacatethechannelwhenalicenseduserisdetected(spec-trummobility).Onceacognitiveradiosupportsthecapabilitytoselectthebestavailablechannel,thenextchallengeistomakethenetworkprotocolsadaptivetotheavailablespectrum.Hence,newfunctionalitiesarerequiredinanxGnetworktosupportthisadaptivity.Insummary,themainfunctionsforcognitiveradiosinxGnetworkscanbesummarizedasfollows:•Spectrumsensing:Detectingunusedspectrumandsharingthespectrumwithoutharmfulinter-ferencewithotherusers.•Spectrummanagement:Capturingthebestavail-ablespectrumtomeetusercommunicati