signal processing techniques for software radio-chp5

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1、Chapter5MultirateSignalProcessingInasoftwaredefinedradio,oneoftenhastodealwithsampledwidebandsignalsthatcontainamultitudeofdifferentusersignals.Partofthereceiver’staskisthustoextractthedesiredusersignal(s)fromsuchawidebandsignal.Insuchcases,thereceivermayconsistofmultiplestagesofdownconversionandfi

2、ltering.Aftereachdownconversionandfilteringstage,theoutputsignalhasalowerNyquistfrequencythantheinput.Thus,itthusmaybedecimatedbeforeanyfurtherprocessing.Asaresult,onehastodealwithsignalprocessingscenarioswheresignalswithmultipleratesaretobedealtwith.Thischapterdiscussesthesignalprocessingissuest

3、hatarepertinenttosuchscenarios.ThemostbasicblocksinmultiratesignalprocessingareM-folddecimatorandL-foldexpander.ThesealongwiththeirimpactontheresultingsignalspectraareintroducedinSection5.1.Section5.2isdevotedtorate-conversion.Throughinterconnectionofdecimators/expandersandfilters,wedevelopmultir

4、atesignalprocessingstructuresthatallowdigitalresamplingofsampledsignalstovirtuallyanyarbitraryrate.TherulesgoverningtheinterconnectionofsignalprocessingblocksinmultiratesystemsarereviewedinSection5.3.BuildingontheresultsofSection5.3,efficientstructuresforrealizationofmultiratesystems,knownaspolyph

5、asefilters,areintroducedinSection5.4.Multistageimplementation,apowerfulmultiratetechniqueforminimizationofthecomplexityofmultiratesystems,isreviewedinSection5.6.SomeexampleapplicationsofmultiratesignalprocessingtechniquesarepresentedinSection5.8.5.1M-foldDecimatorandL-foldExpander5.1.1M-folddecim

6、atorTheM-folddecimatortakesaninputsequencex[n]andproducestheoutputse-quencexd[n]=x[Mn](5.1)9798MultirateSignalProcessingChap.5whereMisaninteger.Inotherwords,theM-folddecimatoronlykeepsoneoutofeveryMelementsofx[n]andignorestherest.Figure5.1showsthebuildingblockthatiscommonlyusedforpresentationoft

7、heM-folddecimator.AdemonstrationofdecimationforM=2ispresentedinFigure5.2x[n]↓Mxd[n]Figure5.1:M-folddecimator.x[n]−23−3−1012nxd[n]−101nFigure5.2:AdemonstrationofdecimationforM=2.TransformdomainanalysisThez-transformofthedecim