90 lines
3.1 KiB
Mathematica
90 lines
3.1 KiB
Mathematica
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function [rx_datafield,MCS,PSDULength,failCheck,rec_frameNo,estNumerlogy,numeroError] = rx_preambleprocess(rx)
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searchOffset = 0; % Offset from start of waveform in samples
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rxWaveLen = 30000;
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cfg = wlanNonHTConfig('SignalChannelBandwidth',true, ...
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'BandwidthOperation','Static');
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% Generate field indices
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ind = wlanFieldIndices(cfg);
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chanBW = cfg.ChannelBandwidth;
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sr = wlanSampleRate(cfg); % Sample rate
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% while (searchOffset + minPktLen) <= rxWaveLen
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% Packet detection
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threshold = 0.8;
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[pktOffset,M] = wlanPacketDetect(rx,chanBW,searchOffset,threshold);
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plot(M)
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% Adjust packet offset
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pktOffset = searchOffset + pktOffset;
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if isempty(pktOffset) || (pktOffset + ind.LSIG(2) > rxWaveLen)
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error('** No packet detected **');
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end
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% Coarse frequency offset estimation and correction using L-STF
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rxLSTF = rx(pktOffset+(ind.LSTF(1):ind.LSTF(2)), :);
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coarseFreqOffset = wlanCoarseCFOEstimate(rxLSTF,chanBW);
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rx = helperFrequencyOffset(rx,sr,-coarseFreqOffset);
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% Symbol timing synchronization
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searchBufferLLTF = rx(pktOffset+(ind.LSTF(1):ind.LSIG(2)),:);
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pktOffset = pktOffset+wlanSymbolTimingEstimate(searchBufferLLTF,chanBW);
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% Fine frequency offset estimation and correction using L-STF
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rxLLTF = rx(pktOffset+(ind.LLTF(1):ind.LLTF(2)),:);
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fineFreqOffset = wlanFineCFOEstimate(rxLLTF,chanBW);
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rx = helperFrequencyOffset(rx,sr,-fineFreqOffset);
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% Scale the waveform based on L-STF power (AGC)
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gain = 1./(sqrt(mean(rxLSTF.*conj(rxLSTF))));
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rx = rx.*gain;
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% Packet Format Detection
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rxLLTF = rx(pktOffset+(ind.LLTF(1):ind.LLTF(2)),:);
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lltfDemod = wlanLLTFDemodulate(rxLLTF,chanBW);
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lltfChanEst = wlanLLTFChannelEstimate(lltfDemod,chanBW);
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noiseVar = helperNoiseEstimate(lltfDemod);
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% Recover L-SIG field bits
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[rxLSIGBits, failCheck, ~] = wlanLSIGRecover(rx(pktOffset + (ind.LSIG(1):ind.LSIG(2)), :), lltfChanEst, noiseVar, chanBW);
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[MCS,PSDULength] = interpretLSIG(rxLSIGBits);
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rec_frameNo = bi2de(rxLSIGBits(19:24).','right-msb');
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if failCheck % Skip L-STF length of samples and continue searching
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disp('** L-SIG check fail **');
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else
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disp('L-SIG check pass');
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end
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% Recover Numerology field bits
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rxLSTF = rx(pktOffset+(ind.LSTF(1):ind.LSTF(2)), :);
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[estNumerlogy,numeroError] = STS_demod(rxLSTF);
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if numeroError
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disp('** Numerology check fail **');
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else
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disp('Numerology check pass');
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end
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% output data field
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% rx_datafield = rx(pktOffset+(ind.NonHTData(1):ind.NonHTData(2)), :);
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rx_datafield = rx(pktOffset+ind.NonHTData(1):end, :);
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end
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%%
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function [MCS,PSDULength] = interpretLSIG(recLSIGBits)
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% InterpretLSIG Interprets recovered L-SIG bits
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%
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% [MCS,PSDULENGTH] = interpretLSIG(RECLSIGBITS) returns the
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% modulation and coding scheme and PSDU length given the recovered L-SIG
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% bits
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% Rate and length are determined from bits
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rate = double(recLSIGBits(1:3));
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length = double(recLSIGBits(5+(1:12)));
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% MCS rate table, IEEE Std 802.11-2016, Table 17-6.
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R = wlan.internal.nonHTRateSignalBits();
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mcstmp = find(all(bsxfun(@eq,R(1:3,:),rate)))-1;
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MCS = mcstmp(1); % For codegen
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PSDULength = bi2de(length.');
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end
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