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1、-4anyconventionalstatisticalsignalprocessingmethodstreatrandomsignalsasiftheyweresta-sharedbymytisticallystationary,inwhichcasetheparametersaredescribed:(1)oftheunderlyingphysicalmechanismthatgeneratestheenablesgenerationsignalwouldnotvarywithtime.Butformostmanmadesignalsencounteredincommunic
2、ation,telemetry,radar,andsonarsystems,someparametersdovaryperiodicallywithtime.Insomecasesevenmultipleincommlensurate(notharmonicallyrelated)periodicitiesareinvolhed.Ex-amplesincludesinusoidalcarriersinamplitude,phase,andfrequencymodulationsystems,periodickeyingoftheonpropertyforsignalcompon-
3、amplitude,phase,orfrequencyindigitalmodulationsys-indistinctspectralbands.Itistems,andperiodicscanningintelevision,facsirnile,andsomeradarsystems.Althoughinsomecasestheseperi-nthatthesethreepropertiesareodicitiescanbeignoredbysignalprocessors,suchasre-ntmartijestationsofasingleat-ceiverswhich
4、mustdetectthepresenceofsignalsofin-terest,estimatetheirparameters,and/orextr.acttheirattributeisstudied,messages,inmanycasestherecanbemuchtogaininwaysforexploitingittermsofimprovementsinperformanceofthesesignal1processingtasksin-processorsbyrecognizingandexploitingunderlyingpe-tionandestimati
5、onofriodicity.Thistypicallyrequiresthattherandomsignalrmptedmanmadesignalsarebemodeledascyclostationary,inwhichcaset!hestatis-ticalparametersvaryintimewithsingleormultiplepe-riodicities.Thisarticleexplainsthatthecyclostationarityattri-bute,asitisreflectedintheperiodicitiesof(second-order)mome
6、ntsofthesignal,canbeinterpretedintermsofthepropertythatenablesgenerationofspectrallinesfromthel053-58~8/91/0400-00I4sr.oo01991IEEEThismaterialisbaseduponworksupportedbytheNationalScienceFoundationunderGrantNo,MIP-88-12902.14IEEESPMAGAZINEAPRIL1991signalbyputtingitthrougha(quadratic)nonlineart
7、rans-formation.Italsoexplainsthefundamentallinkbetweenthespectral-linegenerationpropertyandthestatisticalpropertycalledspectralcorrelation,whichcorrespondstothecorrelationthatexistsbetweentherandomfluc-tuationsofcomponentsofthesignalresidingi