wlanLSIGRecover

Recover L-SIG information transmitted in a noisy 2x2 MIMO channel, and calculate the number of bit errors present in the received information bits.

Set the channel bandwidth and sample rate.

chanBW = "CBW40";
fs = 40e6;

Create a VHT configuration object corresponding to a 40 MHz 2x2 MIMO channel.

cfg = wlanVHTConfig( ...
    ChannelBandwidth=chanBW, ...
    NumTransmitAntennas=2, ...
    NumSpaceTimeStreams=2);

Generate the L-LTF and L-SIG field signals.

txLLTF = wlanLLTF(cfg);
[txLSIG,txLSIGData] = wlanLSIG(cfg);

Create a 2x2 TGac channel

tgacChan = wlanTGacChannel(SampleRate=fs,ChannelBandwidth=chanBW, ...
    NumTransmitAntennas=2,NumReceiveAntennas=2,NormalizeChannelOutputs=false);

Pass the signals through the noisy 2x2 multipath fading channel.and add noise

snrdB = 10; % SNR (dB)
% Convert the SNR per active subcarrier to total SNR to account for noise energy in null subcarriers
ofdmInfo = wlanVHTOFDMInfo("VHT-LTF",cfg);
snrValue = convertSNR(snrdB,"snrsc","snr",FFTLength=ofdmInfo.FFTLength,NumActiveSubcarriers=ofdmInfo.NumTones);
nVar = 10^((-snrValue-30)/10); % Noise variance (W) for 0 dBm (-30 dBW) signal power
rxLLTF = awgn(tgacChan(txLLTF),snrValue);
rxLSIG = awgn(tgacChan(txLSIG),snrValue);

Perform channel estimation based on the L-LTF.

demodLLTF = wlanLLTFDemodulate(rxLLTF,chanBW,1);
chanEst = wlanLLTFChannelEstimate(demodLLTF,chanBW);

Recover the L-SIG information bits.

rxLSIGData = wlanLSIGRecover(rxLSIG,chanEst,nVar,chanBW);

Verify that there are no bit errors in the recovered L-SIG data.

numErrors = biterr(txLSIGData,rxLSIGData)

numErrors = 
0

Recover L-SIG information using the zero-forcing equalizer algorithm. Calculate the number of bit errors in the received data.

Create an HT configuration object.

cfgHT = wlanHTConfig;

Generate the L-SIG field and pass it through an AWGN channel.

[txLSIG,txLSIGData] = wlanLSIG(cfgHT);
rxSIG = awgn(txLSIG,20);

Recover the L-SIG field using the zero-forcing algorithm. The channel estimate is a vector of ones because fading was not introduced.

chanEst = ones(52,1);
nVar = 0.1;
rxLSIGData = wlanLSIGRecover(rxSIG,chanEst,nVar,"CBW20",EqualizationMethod="ZF");

Verify that there are no bit errors in the recovered L-SIG data.

numErrors = biterr(txLSIGData,rxLSIGData)

numErrors = 
0

Recover the L-SIG field from a channel that introduces a fixed phase and frequency offset.

Create a VHT configuration object corresponding to a 160 MHz SISO channel. Generate the transmitted L-SIG field.

cfgVHT = wlanVHTConfig(ChannelBandwidth="CBW160");
txLSIG = wlanLSIG(cfgVHT);

To introduce a 45 degree phase offset and a 100 Hz frequency offset, create a phase and frequency offset System object.

pfOffset = comm.PhaseFrequencyOffset(SampleRate=160e6,PhaseOffset=45, ...
    FrequencyOffset=100);

Introduce phase and frequency offsets to the transmitted L-SIG field, then pass it through an AWGN channel.

rxSIG = awgn(pfOffset(txLSIG),20);

Recover the L-SIG information bits, the failure check status, and the equalized symbols, disabling pilot phase tracking.

chanEst = ones(416,1);
nVar = 0.01;
[recBits,failCheck,eqSym] = wlanLSIGRecover(rxSIG,chanEst,nVar,"CBW160",PilotPhaseTracking="None");

Verify that the L-SIG passed the failure checks.

disp(failCheck)

   0

Visualize the phase offset by plotting the equalized symbols.

scatterplot(eqSym)
grid