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正确的符号正时和多普勒偏移

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Correct symbol timing and frequency offset errors by using thecomm.SymbolSynchronizerandcomm.CarrierSynchronizerSystem objects.

Configuration

Initialize simulation parameters.

M = 16;% Modulation ordernSym = 2000;% Number of symbols in a packetsps = 2;% Samples per symbolspsFilt = 8;每个符号的示例示例和频道的样本spsSync = 2;% Samples per symbol for synchronizerslenFilt = 10;% RRC filter length

Create a matched pair of root raised cosine (RRC) filter System objects for transmitter and receiver.

txfilter = comm.RaisedCosineTransmitFilter(“ Filterspaninsymbols”,lenFilt,...'OutputSamplesPerSymbol',spsFilt,“获得”,sqrt(spsFilt)); rxfilter = comm.RaisedCosineReceiveFilter(“ Filterspaninsymbols”,lenFilt,...'InputSamplesPerSymbol',spsFilt,'DecimationFactor',spsFilt/2,“获得”,sqrt(1/spsFilt));

Create a phase-frequency offset System object to introduce a 100 Hz Doppler shift.

doppler = comm.PhaseFrequencyOffset('FrequencyOffset',100,...'PhaseOffset',45,'SampleRate',1e6);

Create a variable delay System object to introduce timing offsets.

vardelay = dsp.VariableFractionalDelay;

Create carrier and symbol synchronizer System objects to correct for Doppler shift and timing offset, respectively.

carrierSync = comm.CarrierSynchronizer('SamplesPerSymbol',spsSync); symbolSync = comm.SymbolSynchronizer(...'TimingErrorDetector','Early-Late (non-data-aided)',...'SamplesPerSymbol',spsSync);

Create constellation diagram System objects to view the results.

refConst = qammod(0:M-1,M,'UnitAveragePower',真正的);cdReceive = comm.ConstellationDiagram('ReferenceConstellation',refConst,...'SamplesPerSymbol',spsFilt,'Title','Received Signal'); cdDoppler = comm.ConstellationDiagram('ReferenceConstellation',refConst,...'SamplesPerSymbol',spsSync,'Title',“频率校正信号”); cdTiming = comm.ConstellationDiagram('ReferenceConstellation',refConst,...'SamplesPerSymbol',spsSync,'Title',“频率和正时同步信号”);

Main Processing Loop

The main processing loop:

  • Generates random symbols and applies QAM modulation.

  • Filters the modulated signal.

  • Applies frequency and timing offsets.

  • Passes the transmitted signal through an AWGN channel.

  • Filters the received signal.

  • Corrects the Doppler shift.

  • Corrects the timing offset.

fork = 1:15 data = randi([0 M-1],nSym,1); modSig = qammod(data,M,'UnitAveragePower',真正的);txSig = txfilter(modSig); txDoppler = doppler(txSig); txDelay = varDelay(txDoppler,k/15); rxSig = awgn(txDelay,25); rxFiltSig = rxfilter(rxSig); rxCorr = carrierSync(rxFiltSig); rxData = symbolSync(rxCorr);end

Visualization

绘制接收信号的星座图，频率校正信号以及频率和正时同步信号。特定的星座点无法在接收的信号中识别，并且只能在频率校正信号中部分识别。但是，定时和频率同步信号与预期的QAM星座点对齐。

cdReceive(rxSig)

cdDoppler(rxCorr)

cdTiming(rxData)

See Also

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