FSK传输系统实验.docx
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FSK传输系统实验
FSKtransmissionsystemexperiment
1.Theexperimentpurpose
1.UnderstandthebasicworkingprincipleofFSKmodulation.
2.TomasterthebasicworkingprincipleofFSKorthogonalmodulationandtheimplementationprocess.
3.MasteringtheFSKperformancetest.
4.ThebasicpropertiesoftheunderstandingofFSKundernoise.
2.Experimentalapparatus
1.JH5001communicationprinciple,integratedexperimentsystem
2.20MHZoscilloscope
3.JH9001typeerrortester
3.Theexperimentalprinciple
1.FSKmodulation
Inbinaryfrequencyshiftkeying,constantamplitudeofthecarriersignalfrequencywiththechangeoftheinputstreamandswitch(knownasthetrebleandbass,representingbinary1sand0s).Usually,theexpressionofFSKsignalareasfollows:
(binary1)
(binary0)
The2πΔfrepresentsaconstantoffsetofthesignalcarrier.
IsthesimplestwayofFSKsignalbasedontheinputdatabitis0or1,switchinthetwoindependentoscillator.Usingthemethodofwaveformatthemomentofswitchingphaseisdiscontinuous,sotheFSKsignaliscalleddiscontinuousFSKsignal.DiscreteexpressionsforFSKsignal:
(binary1)
(binary0)
Itsimplementationisshowninfigure3.11:
Figure3.11noncontinuousphaseFSKmodulationblockdiagram
Duetotheexpansionofphasediscontinuitymadespectrum,theFSKmodulationmodeintraditionalcommunicationequipmentusedmore.Withnodevelopmentofdigitalprocessingtechnology,evenafterthephaseFSKmodulationtechnologyareusedmoreandmore.
AtpresentcommonlyusedmethodistheFSKsignal,FSKbasebandsignalfirst,basebandsignalisusedtoanalysethesinglecarrierwaveoscillatorfrequencymodulation.Therefore,FSKcanbeexpressedasfollows:
Itshouldbenotedthatalthoughthemodulationwaveformm(t)discretewhenbittransformation,butthephasefunctionistheta(t)andm(t)isproportionaltotheintegral,soitisacontinuous,itscorrespondingwaveformasshowninfigure3.12:
Figure3.12continuousphaseFSKmodulationsignal
AsaresultoftheFSKsignalcomplexenvelopeisthenonlinearfunctionofmodulationsignalm(t),toidentifyaspectrumofFSKsignalisusuallyverydifficult,oftenadoptthemethodofaveragereal-timemeasurement.BinaryFSKsignalpowerspectraldensityofthediscretefrequencycomponentfc,fc+nΔf,fc-nΔf,wherenisaninteger.ContinuousphaseFSKsignalpowerspectraldensityfunctionoffinallyaccordingtothefrequencyoffsetminusfourpowerdecline.Ifthephasediscontinuity,powerspectraldensityfunctionaccordingtothefrequencyoffsetthenegativequadraticpowerdecline.
TheFSKsignalspectrumisshowninfigure3.13.
Figure3.13spectrumofFSKsignal
FSKsignaltransmissionbandwidthofBr,givenbyCarsonformula:
Br=2Δf+2B
OneoftheBforthedigitalbasebandsignalbandwidth.Assumesthatthesignalbandwidthlimitsthescopeofmainlobe,thebandwidthoftherectangularpulsesignalB=R.Therefore,FSKtransmissionbandwidthto:
Br=2(Δf+R)
Iftheascendingcosinepulsefilter,transmissionbandwidthreducedto:
Br=2Δf+(1+α)R
Theαrollreductionfactorforfilter.
Inthecommunicationchannelplatform,FSKmodulationschemeisasfollows:
FSKsignal:
Itis:
Amongthem:
Ifthequantizedtreatmenttothejunction,thesamplingrateforfs,cycleforTs,haveestablishedundertype:
Accordingtotheaboveprinciple,therealizationoftheFSKquadraturemodulatorfor3.14structureasshowninfigure:
Figure3.14FSKquadraturemodulatorstructure
Ifsenda0,thephaseaccumulatoronthebasisofayardbeforetheyuanattheendofthephase,arriveateachsamplingtimephaseaccumulation,untiltheendoftheelement;Ifsend1yd,thephaseaccumulatorbasedonyardbeforetheyuanattheendofthephase,arriveateachsamplingtimephaseaccumulation,untiltheendoftheelement.
IncommunicationchannelmodelofFSKbasebandsignalinmarkingthe32KHZfrequency,spaceusing16KHZfrequency,datatransferrateof8KBPS.
Controllerprovidesthedatasourcesare:
1.Plusdata:
throughthechannelinterfacemoduleprovidesdata.
2.Allcode:
1cantestmarksendfrequency.
3.Zero:
allcantestspacesendingfrequency.
4.01code:
0101...Alternatetype,usedasageneraltest.
5.Specialcodesequence:
cycleof8codesequence,sothattheconventionaloscilloscopetoobserve.
6.Msequence:
canbeusedtochannelperformancetest.
ThestructureoftheFSKmodulatorasshowninfigure3.15:
Figure3.15FSKmodulatorstructurediagram
2.FSKdemodulation
ForFSKsignaldemodulationwaymany:
coherentdemodulation,filternoncoherentdemodulation,orthogonalmultiplicationofnoncoherentdemodulation.
1.FSKcoherentdemodulation
FSKcoherentdemodulationwanttorestorethemarkingfrequency(
)andthespacefrequency(
),restorethecarriersignalandreceivingtheFSKofintermediatefrequencysignalmultiplicationrespectively,andthenwithinaelementpointsrespectively,afterintegralresultispresupposed,ifthedifferenceiscurrentlyreceivingsignalsgivengreaterthan0to1,otherwise0.CoherentFSKdemodulationblockdiagramasshowninfigure3.21:
Figure3.21coherentFSKdemodulationblockdiagram
CoherentFSKdemodulatorisbestunderadditivewhitegaussiannoisechannelreceiving,itserrorrateis:
CoherentFSKdemodulationunderadditivewhitegaussiannoisehasgoodperformance,butundertheotherchannelcharacteristicisnotexactlythesame,suchasunderthewirelessfadingchannel,theperformanceispoorer,generallyUSESnoncoherentdemodulationscheme.
2.FSKfilteringofnoncoherentdemodulation
CommonlyusedforFSKnoncoherentdemodulationfilternoncoherentdemodulation,asshowninfigure3.22.InputFSKintermediatefrequencysignalis
、
respectively,afterthecenterfrequencyandbandpassfilter,andthenthroughtheenvelopedetectionrespectively,theoutputoftheenvelopedetectionatt=kTbsampling(includingkasaninteger),andcomparedthesevalues.Accordingtothesizeoftheenvelopedetectoroutput,comparatordecisiondatabitsare1or0.
Figure3.22incoherentFSKreceiverblockdiagram
WhenusingthenoncoherentdetectionFSKsystemofaveragebiterrorrateis:
InwhitegaussiannoisechannelenvironmentnoncoherentdemodulationFSKfilteringperformanceiscoherentFSKperformanceispoor,butinwirelessfadingenvironment,FSKfilteringnoncoherentdemodulationhasshowngoodrobustness.
NoncoherentdemodulationmethodgenerallyUSESFSKfilteringsimulationmethod,thismethodisnotsuitablefordigitaldemodulationofFSK.FordigitalrealizationmethodoftheFSKgeneralorthogonalmultiplicationmethod.
3.OrthogonalmultiplicationofFSKnoncoherentdemodulation
OrthogonalmultiplicationofFSKnoncoherentdemodulationblockdiagramasshowninfigure3.2-3:
Figure3.23FSKorthogonalmultiplicationofnoncoherentdemodulationschemes
Fortheinputsignal
Markfrequencyasfollows:
Thespacefrequencyis:
Inthediagramabove,timedelaysignalis:
Theτforthedelay.
Aftermultiplyingresultsasfollows:
Inthetype,thefirstafterlowpassfiltercanfilterout.When
Thetypecanbesimplifiedas:
Soafterintegrator(lowpassfilter),theoutputsignalofsize:
soastorealizetheorthogonalmultiplicationofFSKnoncoherentdemodulation.
ABtwowaveformasshowninfigure3.24:
Figure3.24differentialdemodulationwaveform
SeeatimingrecoveryinFSKBPSKdemodulationmethod.
In‘communicationchannelplatform’FSKmode,samplingrateof96KHZsamplingrate(everybitby16samples),FSKbasebandsignalcarrierfrequencyfor24KHZ,thereforeintheprocessofDSPprocessing,sampletaking1timedelayvalue.
TheFSKdemodulationblockdiagramasshowninfigure3.25:
Figure3.25FSKdemodulationblockdiagram
4.Theexperimentcontent
Testbeforeinspection,communicationprincipleoftheintegratedexperimentsystemmodesettoFSKmodulationtransmissionsystem.TPMZ07signaltestpointsismeasuredwiththeoscilloscope,ifthereisapulsewaveform,experimentalsystemhasbeennormalwork.Ifthereisnopulsewaveform,theneedtopresstheresetbuttononthepaneltoinitializedtohardware.
1.FSKmodulation
1.FSKbasebandsignalobservation
TPi03isbasebandFSKwaveform.Throughthemenuchoicefor1codeinputdatasignal,theobservedTPi03signalwaveform,measuringthebasebandsignalcycleandsymbolrate.
Throughthemenuchoiceforzeroinputdatasignals,observationTPi03signalwaveform,measuringthebasebandsignalcycle.Measurementresultswillbecomparedwith1yards.
1.Originatedinphasebranchandorthogonalbranchsignaltimedomainwaveformobservations
TPi03andTPi04werebasebandFSKoutputsignalsofin-phasebranchandorthogonalbranch.Measuringthetwosignalsinthetimedomainwaveformwillenter1yards,measuringthetwosignalwhethermeettheorthogonalrelation.
2.OriginatedinphaseLiShaeducationbranchandorthogonalbranchsignal(x-y)waveformobservations
Settheoscilloscopein(x,y),canbeobservedfromthephaseplaneTPi03andTPi04orthogonality,anditsLiShaeducationshouldbeacircle.
Throughthemenuchoicemeasuredunderdifferentinputtype.
3.ContinuousphaseFSKmodulationbasebandsignalobservation
TPM02issendingdatasignals,TPi03isbasebandFSKwaveform.Measurement,throughthemenuchoose0/1codeinputdatasignals,andtheTPM02assynchronoussignal.ObservationTPM02withTPi03pointwaveformcorrespondingrelationshipshouldhaveaclearsignal.And,intheelementofswitchingpointsendwaveformphasecontinuous.
Throughthemenuselectionforaparticularsequencecodeinputdatasignal,repeatth