wlanVHTLTFDemodulate

Create a VHT format configuration object.

vht = wlanVHTConfig;

Generate a VHT-LTF signal.

txVHTLTF = wlanVHTLTF(vht);

Add white noise to the signal.

rxVHTLTF = awgn(txVHTLTF,1);

Demodulate the received signal.

y = wlanVHTLTFDemodulate(rxVHTLTF,vht);

Specify a VHT format configuration object and generate a VHT-LTF.

vht = wlanVHTConfig;
txltf = wlanVHTLTF(vht);

Multiply the transmitted VHT-LTF by 0.1 + 0.1i. Pass the signal through an AWGN channel.

rxltfNoNoise = txltf * complex(0.1,0.1);
rxltf = awgn(rxltfNoNoise,20,'measured');

Demodulated the received VHT-LTF with a symbol offset of 0.5.

dltf = wlanVHTLTFDemodulate(rxltf,vht,0.5);

Estimate the channel using the demodulated VHT-LTF. Plot the result.

chEst = wlanVHTLTFChannelEstimate(dltf,vht);
scatterplot(chEst)

The estimate is very close to the previously introduced 0.1+0.1i multiplier.

Configure a VHT-format configuration object with two paths.

vht = wlanVHTConfig('NumTransmitAntennas',2,'NumSpaceTimeStreams',2);

Generate a random PSDU and create the corresponding VHT waveform.

txPSDU = randi([0 1],8*vht.PSDULength,1);
txSig = wlanWaveformGenerator(txPSDU,vht);

Pass the signal through a TGac 2x2 MIMO channel.

tgacChan = wlanTGacChannel('NumTransmitAntennas',2,'NumReceiveAntennas',2, ...
    'LargeScaleFadingEffect','Pathloss and shadowing');
rxSigNoNoise = tgacChan(txSig);

Add AWGN to the received signal. Set the noise variance for the case in which the receiver has a 9-dB noise figure.

nVar = 10^((-228.6+10*log10(290)+10*log10(80e6)+9)/10);
awgnChan = comm.AWGNChannel('NoiseMethod','Variance','Variance',nVar);
rxSig = awgnChan(rxSigNoNoise);

Determine the indices for the VHT-LTF and extract the field from the received signal.

indVHT = wlanFieldIndices(vht,'VHT-LTF');
rxLTF = rxSig(indVHT(1):indVHT(2),:);

Demodulate the VHT-LTF and estimate the channel coefficients.

dLTF = wlanVHTLTFDemodulate(rxLTF,vht);
chEst = wlanVHTLTFChannelEstimate(dLTF,vht);

Extract the VHT-Data field and recover the information bits.

indData = wlanFieldIndices(vht,'VHT-Data');
rxData = rxSig(indData(1):indData(2),:);
rxPSDU = wlanVHTDataRecover(rxData,chEst,nVar,vht);

Determine the number of bit errors.

numErrs = biterr(txPSDU,rxPSDU)

numErrs = 
0

Recover bits from the VHT-Data field of a VHT multi-user transmission recovered from a fading MU-MIMO channel by using channel estimation on the VHT-LTF.

This example can return high bit error rates because the transmission does not include precoding to mitigate the interference between space-time streams. However, the example shows a typical VHT signal recovery workflow and appropriate syntax use for the functions.

Configure a VHT transmission with a channel bandwidth of 160 MHz, two users, and four transmit antennas. Assign one space-time stream to the first user and three space-time streams to the second user.

cbw = 'CBW160';
numSTS = [1 3];
cfgVHT = wlanVHTConfig('ChannelBandwidth',cbw,'NumUsers',2, ...
    'NumTransmitAntennas',4,'NumSpaceTimeStreams',numSTS);

Generate a payload of bits for each user. This payload must be in a 1-by-N cell array, where N is the number of users.

psduLength = 8*cfgVHT.PSDULength;
numUsers = cfgVHT.NumUsers;
bits = cell(1,2);
for nu = 1:numUsers
    bits{nu} = randi([0 1],psduLength(nu),1);
end

Generate VHT-LTF and VHT-Data field signals.

txLTF  = wlanVHTLTF(cfgVHT); 
txDataSym = wlanVHTData(bits,cfgVHT);

Pass the VHT-Data field signal for the first user through a 4x1 channel because this signal consists of a single space-time stream. Pass the VHT-Data field for the second user through a 4x3 channel because this signal consists of three space-time streams. Apply AWGN to each signal, assuming an SNR of 15 dB.

snr = 15; 
H{1} = complex(randn(4,1),randn(4,1))/sqrt(2);
H{2} = complex(randn(4,3),randn(4,3))/sqrt(2);
number = zeros(2,1);
ratio = zeros(2,1);
for userIdx = 1:numUsers
    rxDataSym = awgn(txDataSym*H{userIdx},snr,'measured');

Apply the same channel processing to the VHT-LTF for each user.

    rxLTF = awgn(txLTF*H{userIdx},snr,'measured');

Calculate the received signal power for each user and estimate the noise variance.

    powerDB = 10*log10(var(rxDataSym));
    noiseVarEst = mean(10.^(0.1*(powerDB-snr)));

Estimate the channel characteristics by using the VHT-LTF.

    demod = wlanVHTLTFDemodulate(rxLTF,cbw,numSTS);
    chEst = wlanVHTLTFChannelEstimate(demod,cbw,numSTS);

Recover the bits from the received VHT-Data field for each user and determine the bit error rate by comparing the recovered bits with the original payload bits.

    dataBits = wlanVHTDataRecover(rxDataSym,chEst,noiseVarEst,cfgVHT,userIdx);
    [number(userIdx),ratio(userIdx)] = biterr(bits{userIdx},dataBits);
    disp(number(userIdx))
    disp(ratio(userIdx))
end

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