802.11be Packet Error Rate Simulation for an EHT MU Single-User Packet Format

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This example shows how to measure the packet error rate of an IEEE® 802.11be™ (Wi-Fi 7) extremely high throughput multi-user (EHT MU) packet format link with a single user.

Introduction

This example determines the packet error rate for an 802.11be [ 1 ] single-user (SU) link by using an end-to-end simulation for a selection of signal-to-noise ratio (SNR) points. At each SNR point, the example simulates the transmission of multiple packets through a noisy TGax indoor channel, then demodulates the received packets and recovers the PSDUs. The example then compares the transmitted and received packets to determine the packet error rate. This diagram shows the processing steps for each packet.

Waveform Configuration

An EHT MU SU packet is a full-band transmission to a single user. Configure the transmission parameters for an SU packet format by using the wlanEHTMUConfig object. The properties of the object contain the physical layer (PHY) configuration.

Create a configuration object for an EHT MU transmission, setting a channel bandwidth of 20 MHz, an APEP length of 1000 bytes, two transmit antennas, two space-time streams, and a modulation and coding scheme (MCS) value of 13, which specifies 4096-point quadrature amplitude modulation (4096-QAM) and a coding rate of 5/6. If you specify mcs as a vector, the example performs the simulation for each MCS index value.

chanBW = 'CBW20';                           % Channel bandwidth
cfgEHT = wlanEHTMUConfig(chanBW);
cfgEHT.User{1}.APEPLength = 1e3;            % APEP length (bytes)
numTx = 2;                                  % Number of transmit antennas
numRx = 2;                                  % Number of receive antennas
cfgEHT.NumTransmitAntennas = numTx;
cfgEHT.User{1}.NumSpaceTimeStreams = numTx; % Number of space-time streams
mcs = 13;                                   % MCS index

Channel Configuration

This example uses a TGax non-line-of-sight (NLOS) indoor channel model with delay profile Model-B. Model-B is considered NLOS when the distance between transmitter and receiver is greater than or equal to 5 meters. For more information about the TGax channel model, see wlanTGaxChannel.

% Create and configure a 2x2 MIMO channel.
tgaxChannel = wlanTGaxChannel;
tgaxChannel.DelayProfile = 'Model-B';
tgaxChannel.NumTransmitAntennas = cfgEHT.NumTransmitAntennas;
tgaxChannel.NumReceiveAntennas = numRx;
tgaxChannel.TransmitReceiveDistance = 5; % Distance in meters for NLOS
tgaxChannel.ChannelBandwidth = chanBW;
tgaxChannel.LargeScaleFadingEffect = 'None';
fs = wlanSampleRate(chanBW);
tgaxChannel.SampleRate = fs;

Simulation Parameters

For each SNR point in snrRange, the example generates the specified number of packets, passes the packets through a channel, then demodulates the received signal to determine the packet error rate. Set the SNR values in the snrRange parameter to simulate the transition from all packets being decoded in error to all packets being decoded successfully as the SNR value increases for MCS 13. If you specify snrRange as a matrix, each row represents the SNR points for the corresponding MCS index, defined in mcs.

snrRange = 37:5:57; % Set the range of SNR values

These parameters control the number of packets tested for each SNR point.

maxNumErrors: the maximum number of packet errors simulated for each SNR point. When the number of packet errors reaches this limit, the simulation at this SNR point is complete.
maxNumPackets: the maximum number of packets simulated for each SNR point, which limits the length of the simulation if the simulation does not reach the packet error limit.

The default parameter values lead to a very short simulation. For meaningful results, increase these values.

maxNumErrors = 10;
maxNumPackets = 100;

Processing SNR Points

This section measures the packet error rate for each SNR point by performing these processing steps for the specified number of packets.

Create a PSDU and encode to generate a single-packet waveform.
Pass the waveform through an indoor TGax channel model, using different channel realizations for each packet.
Add AWGN to the received waveform to create the desired average SNR per subcarrier after OFDM demodulation. The configuration accounts for the normalization within the channel by the number of receive antennas and the noise energy in unused subcarriers. The example removes the unused subcarriers during OFDM demodulation.
Detect the packet
Estimate and correct coarse carrier frequency offset (CFO)
Perform fine timing synchronization by using L-STF, L-LTF, and L-SIG samples. This synchronization enables packet detection at the start or end of the L-STF.
Estimate and correct fine CFO
Extract the EHT-LTF from the synchronized received waveform
OFDM demodulate the EHT-LTF and perform channel estimation
Extract the data field from the synchronized received waveform and perform OFDM demodulation
Track any residual CFO by performing common phase error pilot tracking
Perform noise estimation by using the demodulated data field pilots and single-stream channel estimation at pilot subcarriers
Equalize the phase corrected OFDM symbols by using channel estimation
Recover the PSDU by demodulating and decoding the equalized symbols

This example also demonstrates how to speed up simulations by using a parfor loop instead of a for loop when simulating each SNR point. The parfor function executes processing for each SNR in parallel to reduce the total simulation time. Use a parfor loop to parallelize processing of the SNR points. To use parallel computing for increased speed, comment out the for statement and uncomment the parfor statement in this code.

numSNR = size(snrRange,2); % Number of SNR points
numMCS = numel(mcs); % Number of MCS
packetErrorRate = zeros(numMCS,numSNR);

for imcs = 1:numel(mcs)
    cfgEHT.User{1}.MCS = mcs(imcs);
    ofdmInfo = wlanEHTOFDMInfo('EHT-Data',cfgEHT);
    % SNR points to simulate from MCS
    snr = snrRange(imcs,:);
    ind = wlanFieldIndices(cfgEHT);

    %parfor isnr = 1:numSNR % Use parfor to speed up the simulation
    for isnr = 1:numSNR % Use for to debug the simulation
                        % Set random substream index per iteration to ensure that each
                        % iteration uses a repeatable set of random numbers
        stream = RandStream('combRecursive','Seed',99);
        stream.Substream = isnr;
        RandStream.setGlobalStream(stream);

        % Convert the SNR per active subcarrier to total SNR to account for
        % noise energy in nulls
        snrValue = convertSNR(snr(isnr),"snrsc","snr",...
            FFTLength=ofdmInfo.FFTLength,...
            NumActiveSubcarriers=ofdmInfo.NumTones);

        % Loop to simulate multiple packets
        numPacketErrors = 0;
        numPkt = 1; % Index of packet transmitted
        while numPacketErrors<=maxNumErrors && numPkt<=maxNumPackets
            % Generate waveform
            txPSDU = randi([0 1],psduLength(cfgEHT)*8,1); % PSDULength (bytes)
            tx = wlanWaveformGenerator(txPSDU,cfgEHT);

            % Add trailing zeros to allow for channel delay
            txPad = [tx; zeros(50,cfgEHT.NumTransmitAntennas)];

            % Pass through fading indoor TGax channel
            reset(tgaxChannel); % Reset channel for different realization
            rx = tgaxChannel(txPad);

            % Pass waveform through an AWGN channel
            rx = awgn(rx,snrValue);

            % Detect packet and determine coarse packet offset
            coarsePktOffset = wlanPacketDetect(rx,chanBW);
            if isempty(coarsePktOffset) % If empty no L-STF detected, packet error
                numPacketErrors = numPacketErrors+1;
                numPkt = numPkt+1;
                continue; % Go to next loop iteration
            end

            % Extract L-STF and perform coarse frequency offset correction
            lstf = rx(coarsePktOffset+(ind.LSTF(1):ind.LSTF(2)),:);
            coarseFreqOff = wlanCoarseCFOEstimate(lstf,chanBW);
            rx = frequencyOffset(rx,fs,-coarseFreqOff);

            % Extract the non-HT fields and determine fine packet offset
            nonhtfields = rx(coarsePktOffset+(ind.LSTF(1):ind.LSIG(2)),:);
            finePktOffset = wlanSymbolTimingEstimate(nonhtfields,chanBW);

            % Determine final packet offset
            pktOffset = coarsePktOffset+finePktOffset;

            % If packet detected outwith range of expected delays from
            % the channel modeling, packet error
            if pktOffset>50
                numPacketErrors = numPacketErrors+1;
                numPkt = numPkt+1;
                continue; % Go to next loop iteration
            end

            % Extract L-LTF and perform fine frequency offset correction
            rxLLTF = rx(pktOffset+(ind.LLTF(1):ind.LLTF(2)),:);
            fineFreqOff = wlanFineCFOEstimate(rxLLTF,chanBW);
            rx = frequencyOffset(rx,fs,-fineFreqOff);

            % EHT-LTF demodulation and channel estimation
            rxHELTF = rx(pktOffset+(ind.EHTLTF(1):ind.EHTLTF(2)),:);
            heltfDemod = wlanEHTDemodulate(rxHELTF,'EHT-LTF',cfgEHT);
            [chanEst,pilotEst] = wlanEHTLTFChannelEstimate(heltfDemod,cfgEHT);

            % Demodulate the Data field
            rxData = rx(pktOffset+(ind.EHTData(1):ind.EHTData(2)),:);
            demodSym = wlanEHTDemodulate(rxData,'EHT-Data',cfgEHT);

            % Perform pilot phase tracking
            demodSym = wlanEHTTrackPilotError(demodSym,chanEst,cfgEHT,'EHT-Data');

            % Estimate noise power in EHT fields
            nVarEst = wlanEHTDataNoiseEstimate(demodSym(ofdmInfo.PilotIndices,:,:),pilotEst,cfgEHT);

            % Extract data subcarriers from demodulated symbols and channel
            % estimate
            demodDataSym = demodSym(ofdmInfo.DataIndices,:,:);
            chanEstData = chanEst(ofdmInfo.DataIndices,:,:);

            % Equalization
            [eqSym,csi] = wlanEHTEqualize(demodDataSym,chanEstData,nVarEst,cfgEHT,'EHT-Data');

            % Recover data field bits
            rxPSDU = wlanEHTDataBitRecover(eqSym,nVarEst,csi,cfgEHT);

            % Determine if any bits are in error
            packetError = any(biterr(txPSDU,rxPSDU));
            numPacketErrors = numPacketErrors+packetError;
            numPkt = numPkt+1;
        end

        % Calculate PER at SNR point
        packetErrorRate(imcs,isnr) = numPacketErrors/(numPkt-1);
        disp(['MCS ' num2str(mcs(imcs)) ','...
              ' SNR ' num2str(snr(isnr)) ...
              ' completed after ' num2str(numPkt-1) ' packets,'...
              ' PER:' num2str(packetErrorRate(imcs,isnr))]);
    end
end

MCS 13, SNR 37 completed after 11 packets, PER:1
MCS 13, SNR 42 completed after 11 packets, PER:1
MCS 13, SNR 47 completed after 23 packets, PER:0.47826
MCS 13, SNR 52 completed after 64 packets, PER:0.17188
MCS 13, SNR 57 completed after 100 packets, PER:0.02

Plot Packet Error Rate vs SNR

markers = 'ox*sd^v><ph+ox*sd^v><ph+';
figure;
for imcs = 1:numMCS
    semilogy(snrRange(imcs,:),packetErrorRate(imcs,:).',['-' markers(imcs)]);
    hold on;
end
grid on;
xlabel('SNR (dB)');
ylabel('PER');
dataStr = arrayfun(@(x)sprintf('MCS %d',x),mcs,'UniformOutput',false);
legend(dataStr,'Location','NorthEastOutside');
title(['PER (EHT MU), ' num2str(cfgEHT.ChannelBandwidth) ', Model-B, ' num2str(numTx) '-by-' num2str(numRx)]);

Further Exploration

The maxNumErrors and maxNumPackets parameters control the number of packets tested for each SNR point. For meaningful results, increase these values. For example, this figure shows results for a channel bandwidth of 320 MHz, an APEP length of 16000 bytes, MCS values of 0-13, a maxNumErrors value of 100, and a maxNumPackets value of 1000. The corresponding SNR values for MCS between 0 and 13 are:

snrRange = [...
    8:1:13; ... % MCS 0
    8:2:18; ... % MCS 1
    16:2:26; ... % MCS 2
    18:2:28; ... % MCS 3
    24:2:34; ... % MCS 4
    26:2:36; ... % MCS 5
    28:2:38; ... % MCS 6
    32:2:42; ... % MCS 7
    34:2:44; ... % MCS 8
    36:2:46; ... % MCS 9
    38:2:48; ... % MCS 10
    42:2:52; ... % MCS 11
    44:2:54; ... % MCS 12
    45:3:60]; ...% MCS 13

Selected Bibliography

IEEE Std 802.11be™/D5.0 Draft Standard for Information technology - Telecommunications and information exchange between systems Local and metropolitan area networks - Specific requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 8: Enhancements for Extremely High Throughput (EHT).