Basic VHT Data Recovery

Basic Data Recovery

WLAN Toolbox™ provides functions to generate and recover IEEE® 802.11ac™ standards-compliant waveforms. The data recovery process comprises these steps.

The block diagram shows these steps, along with their corresponding commands.

Create VHT configuration object.

cfg = wlanVHTConfig;

Create a VHT transmit waveform by using the VHT configuration object. Set the data sequence to [1;0;1;1]. The waveform generator function repeats the data sequence to generate the specified number of packets.

txSig = wlanWaveformGenerator([1;0;1;1],cfg);

Pass the received signal through an AWGN channel.

rxSig = awgn(txSig,10);

Determine the field indices of the waveform.

ind = wlanFieldIndices(cfg);

Extract the VHT-LTF from the received signal.

rxVHTLTF = rxSig(ind.VHTLTF(1):ind.VHTLTF(2),:);

Demodulate the VHT-LTF. Estimate the channel response by using the demodulated signal.

demodVHTLTF = wlanVHTLTFDemodulate(rxVHTLTF,cfg);
chEst = wlanVHTLTFChannelEstimate(demodVHTLTF,cfg);

Extract the VHT data field.

rxData = rxSig(ind.VHTData(1):ind.VHTData(2),:);

Recover the information bits by using the channel and noise variance estimates. Confirm that the first 8 bits match two repetitions of the input data sequence of [1;0;1;1].

rxBits = wlanVHTDataRecover(rxData,chEst,0.1,cfg);

rxBits(1:8)

ans = 8x1 int8 column vector

   1
   0
   1
   1
   1
   0
   1
   1

Data Recovery with Frequency Correction

Data recovery when a carrier frequency offset is present is accomplished by these steps.

The block diagram shows these steps, along with their corresponding commands.

Set the channel bandwidth and sample rate.

cbw = 'CBW160';
fs = 160e6;

Create a VHT configuration object that supports a 2x2 MIMO transmission.

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

Generate a VHT waveform containing a random PSDU.

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

Create a 2x2 TGac channel.

tgacChan = wlanTGacChannel('SampleRate',fs,'ChannelBandwidth',cbw, ...
    'NumTransmitAntennas',2,'NumReceiveAntennas',2);

Create a phase and frequency offset object.

pfOffset = comm.PhaseFrequencyOffset('SampleRate',fs,'FrequencyOffsetSource','Input port');

Pass the transmitted waveform through the noisy TGac channel.

rxSigNoNoise = tgacChan(txSig);
rxSig = awgn(rxSigNoNoise,15);

Introduce a frequency offset of 500 Hz to the received signal.

rxSigFreqOffset = pfOffset(rxSig,500);

Find the start and stop indices for all component fields of the PPDU.

ind = wlanFieldIndices(cfg);

Extract the L-STF. Estimate and correct for the carrier frequency offset.

rxLSTF = rxSigFreqOffset(ind.LSTF(1):ind.LSTF(2),:);

foffset1 = wlanCoarseCFOEstimate(rxLSTF,cbw);
rxSig1 = pfOffset(rxSigFreqOffset,-foffset1);

Extract the L-LTF from the corrected signal. Estimate and correct for the residual frequency offset.

rxLLTF = rxSig1(ind.LLTF(1):ind.LLTF(2),:);

foffset2 = wlanFineCFOEstimate(rxLLTF,cbw);
rxSig2 = pfOffset(rxSig1,-foffset2);

Extract and demodulate the VHT-LTF. Estimate the channel coefficients.

rxVHTLTF = rxSig2(ind.VHTLTF(1):ind.VHTLTF(2),:);
demodVHTLTF = wlanVHTLTFDemodulate(rxVHTLTF,cfg);
chEst = wlanVHTLTFChannelEstimate(demodVHTLTF,cfg);

Extract the VHT data field from the received and frequency-corrected PPDU. Recover the data field.

rxData = rxSig2(ind.VHTData(1):ind.VHTData(2),:);
rxPSDU = wlanVHTDataRecover(rxData,chEst,0.03,cfg);

Calculate the number of bit errors in the received packet.

numErr = biterr(txPSDU,rxPSDU)

numErr = 0