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1、[ZhiQuan,ShuguangCui,H.VincentPoor,andAliH.Sayed]CollaborativeWidebandSensingforCognitiveRadios©BRANDXPICTURES[Anoverviewofchallengesandsolutions]ognitiveradio(CR)hasrecentlyemergedasaprom-articleprovidesanoverviewofthechallengesandpossiblesolu-isingtec
2、hnologytorevolutionizespectrumutiliza-tionsforthedesignofcollaborativewidebandsensinginCRnet-tioninwirelesscommunications.InaCRnetwork,works.Itisarguedthatcollaborativespectrumsensingcansecondaryuserscontinuouslysensethespectralmakeuseofsignalprocessing
3、gainsatthephysicallayertomiti-Cenvironmentandadapttransmissionparameterstogatestrictrequirementsontheradiofrequencyfront-endandtoopportunisticallyusetheavailablespectrum.Afundamentalexploitspatialdiversitythroughnetworkcooperationtosignifi-problemforCRs
4、isspectrumsensing;secondaryusersneedtocantlyimprovesensingreliability.reliablydetectweakprimarysignalsofpossiblydifferenttypesoveratargetedwidefrequencybandinordertoidentifyspectralCOGNITIVERADIOSholesforopportunisticcommunications.ConceptuallyandTradit
5、ionalspectrumallocationpoliciesarefacingscarceradiopractically,thereisgrowingawarenessthatcollaborationamongfrequency(RF)resourcesduetotheproliferationofwirelessseveralCRscanachieveconsiderableperformancegains.Thisservices.Recently,theFederalCommunicati
6、onsCommission(FCC)isdevelopingpoliciesforunlicensedwirelessdevicestoDigitalObjectIdentifier10.1109/MSP.2008.929296opportunisticallyusevacantfrequencybands(seeFigure1),IEEESIGNALPROCESSINGMAGAZINE[60]NOVEMBER20081053-5888/08/$25.00©2008IEEEespeciallyvaca
7、ntTVbroadcastbands[1].Inthiscontext,theENERGYDETECTIONemergingCRtechnologyisconsideredtobeapromisingtech-Thenoncoherentenergydetector(orradiometer)[9]isoneofniquetoimprovespectrumutilizationbyseekingandoppor-thesimplestapproachesfordecidingbetweenH0andH
8、1.Lettunisticallyutilizingresourcesintime,frequency,andspacex=[x(1),x(2),...,x(N)]Tands=[s(1),s(2),...,s(N)]T.domainswithoutcausingharmfulinterferencetolegacysystemsThedecisionruleinthiscaseisgivenby[2].Intheliterature,CRnetworks
