HE/demodSIG.m

%% 解包头
function [cfgRx,cfgUsers,rmsEVM,failCRC] = demodSIG(rx,rx_format,cfgUI)%% Packet Format Detection
%% L-LTF Channel Estimate
% Demodulate the L-LTF and perform channel estimation. The demodulated
% L-LTF symbols include tone rotation for each 20 MHz segment as described
% in [ <#16 2> ], section 21.3.7.5. The L-LTF channel estimates (with tone
% rotation) are used to equalize and decode the pre-HE-LTF fields.

lltfDemod = wlanHEDemodulate(rxLLTF,'L-LTF',chanBW);
lltfChanEst = wlanLLTFChannelEstimate(lltfDemod,chanBW);

%% L-SIG and RL-SIG Decoding
% The L-SIG field is used to determine the receive time, or RXTIME, of the
% packet. The RXTIME is calculated using the length bits of the L-SIG
% payload. The L-SIG and RL-SIG fields are recovered to perform the channel
% estimate on the extra subcarriers in the L-SIG and RL-SIG fields. The
% |lltfChanEst| channel estimates are updated to include the channel
% estimates on extra subcarriers in the L-SIG and RL-SIG fields. The L-SIG
% payload is decoded using an estimate of the channel and noise power
% obtained from the L-LTF field. The L-SIG length property in
% <matlab:edit('wlanHERecoveryConfig.m') wlanHERecoveryConfig> is updated after L-SIG decoding.

disp('Decoding L-SIG... ');
% Extract L-SIG and RL-SIG fields
rxLSIG = rx(pktOffset+(ind.LSIG(1):ind.RLSIG(2)),:);

% OFDM demodulate
helsigDemod = wlanHEDemodulate(rxLSIG,'L-SIG',chanBW);

% Estimate CPE and phase correct symbols
helsigDemod = preHECommonPhaseErrorTracking(helsigDemod,lltfChanEst,'L-SIG',chanBW);

% Estimate channel on extra 4 subcarriers per subchannel and create full
% channel estimate
preheInfo = wlanHEOFDMInfo('L-SIG',chanBW);
preHEChanEst = preHEChannelEstimate(helsigDemod,lltfChanEst,preheInfo.NumSubchannels);

% Average L-SIG and RL-SIG before equalization
helsigDemod = mean(helsigDemod,2);

% Equalize data carrying subcarriers, merging 20 MHz subchannels
[eqLSIGSym,csi] = preHESymbolEqualize(helsigDemod(preheInfo.DataIndices,:,:), ...
    preHEChanEst(preheInfo.DataIndices,:,:),noiseVar,preheInfo.NumSubchannels);

% Decode L-SIG field
[~,failCheck,lsigInfo] = wlanLSIGBitRecover(eqLSIGSym,noiseVar,csi);

if failCheck
    disp(' ** L-SIG check fail **');
else
    disp(' L-SIG check pass');
end
% Get the length information from the recovered L-SIG bits and update the
% L-SIG length property of the recovery configuration object
lsigLength = lsigInfo.Length;
cfgRx.LSIGLength = lsigLength;

% Measure EVM of L-SIG symbols
EVM = comm.EVM;
EVM.ReferenceSignalSource = 'Estimated from reference constellation';
EVM.Normalization = 'Average constellation power';
EVM.ReferenceConstellation = wlanReferenceSymbols('BPSK');
rmsEVM = EVM(eqLSIGSym);
fprintf(' L-SIG EVM: %2.2fdB\n\n',20*log10(rmsEVM/100));

% Calculate the receive time and corresponding number of samples in the
% packet
RXTime = ceil((lsigLength + 3)/3) * 4 + 20; % In microseconds
numRxSamples = round(RXTime * 1e-6 * sr);   % Number of samples in time

fprintf(' RXTIME: %dus\n',RXTime);
fprintf(' Number of samples in the packet: %d\n\n',numRxSamples);

%%
% The waveform and spectrum of the detected packet within |rx| is
% displayed given the calculated RXTIME and corresponding number of
% samples.

sampleOffset = max((-lstfLength + pktOffset),1); % First index to plot
sampleSpan = numRxSamples + 2*lstfLength; % Number samples to plot
% Plot as much of the packet (and extra samples) as we can
plotIdx = sampleOffset:min(sampleOffset + sampleSpan,rxWaveLen);

% Configure timeScope to display the packet 展示
timeScope.TimeSpan = sampleSpan/sr;
timeScope.TimeDisplayOffset = sampleOffset/sr;
timeScope.YLimits = [0 max(abs(rx(:)))];
timeScope(abs(rx(plotIdx,:)));
release(timeScope);

% Display the spectrum of the detected packet 展示
spectrumAnalyzer(rx(pktOffset + (1:numRxSamples),:));
release(spectrumAnalyzer);

%% HE-SIG-A Decoding
% The HE-SIG-A field contains the transmission configuration of an HE
% packet. An estimate of the channel and noise power obtained from the
% L-LTF is required to decode the HE-SIG-A field.

disp('Decoding HE-SIG-A...')
rxSIGA = rx(pktOffset+(ind.HESIGA(1):ind.HESIGA(2)),:);
sigaDemod = wlanHEDemodulate(rxSIGA,'HE-SIG-A',chanBW);
hesigaDemod = preHECommonPhaseErrorTracking(sigaDemod,preHEChanEst,'HE-SIG-A',chanBW);

% Equalize data carrying subcarriers, merging 20 MHz subchannels
preheInfo = wlanHEOFDMInfo('HE-SIG-A',chanBW);
[eqSIGASym,csi] = preHESymbolEqualize(hesigaDemod(preheInfo.DataIndices,:,:), ...
                                      preHEChanEst(preheInfo.DataIndices,:,:), ...
                                      noiseVar,preheInfo.NumSubchannels);
% Recover HE-SIG-A bits
[sigaBits,failCRC] = wlanHESIGABitRecover(eqSIGASym,noiseVar,csi);

% Perform the CRC on HE-SIG-A bits
if failCRC
    disp(' ** HE-SIG-A CRC fail **');
else
    disp(' HE-SIG-A CRC pass');
end

% Measure EVM of HE-SIG-A symbols
release(EVM);
if strcmp(pktFormat,'HE-EXT-SU')
    % The second symbol of an HE-SIG-A field for an HE-EXT-SU packet is
    % QBPSK.
    EVM.ReferenceConstellation = wlanReferenceSymbols('BPSK',[0 pi/2 0 0]);
    % Account for scaling of L-LTF for an HE-EXT-SU packet
    rmsEVM = EVM(eqSIGASym*sqrt(2));
else
    EVM.ReferenceConstellation = wlanReferenceSymbols('BPSK');
    rmsEVM = EVM(eqSIGASym);
end
fprintf(' HE-SIG-A EVM: %2.2fdB\n\n',20*log10(mean(rmsEVM)/100));

%% Interpret Recovered HE-SIG-A bits
% The <matlab:edit('wlanHERecoveryConfig.m') wlanHERecoveryConfig> object
% is updated after interpreting the recovered HE-SIG-A bits. 

cfgRx = interpretHESIGABits(cfgRx,sigaBits);          
ind = wlanFieldIndices(cfgRx); % Update field indices
%%
% Display the common transmission configuration obtained from HE-SIG-A
% field for an HE-MU packet. The properties indicated by -1 are unknown or
% undefined. The unknown user-related properties are updated after
% successful decoding of the HE-SIG-B field.
disp(cfgRx)

%% HE-SIG-B Decoding
% For an HE-MU packet the HE-SIG-B field contains:
%
% * The RU allocation information for a non-compressed SIGB waveform is
% inferred from HE-SIG-B Common field [ <#16 1> Table. 27-23]. For a
% compressed SIGB waveform the RU allocation information is inferred from
% the recovered HE-SIG-A bits.
% * For a non-compressed SIGB waveform the number of HE-SIG-B symbols are
% updated in the <matlab:edit('wlanHERecoveryConfig.m') wlanHERecoveryConfig> object. 
% The symbols are only updated if the number of HE-SIG-B symbols indicated
% in the HE-SIG-A field is set to 15 and all content channels pass the CRC.
% The number of HE-SIG-B symbols indicated in the HE-SIG-A field are not
% updated if any HE-SIG-B content channel fails the CRC.
% * The user transmission parameters for both SIGB compressed and
% non-compressed waveforms are inferred from the HE-SIG-B user field [ <#16 1>
% Table. 27-25, 27-26].
%
% An estimate of the channel and noise power obtained from the L-LTF is
% required to decode the HE-SIG-B field.

if strcmp(pktFormat,'HE-MU')
    fprintf('Decoding HE-SIG-B...\n');
    if ~cfgRx.SIGBCompression
        fprintf(' Decoding HE-SIG-B common field...\n');
        s = getSIGBLength(cfgRx);
        % Get common field symbols. The start of HE-SIG-B field is known
        rxSym = rx(pktOffset+(ind.HESIGA(2)+(1:s.NumSIGBCommonFieldSamples)),:);
        % Decode HE-SIG-B common field
        [status,cfgRx] = heSIGBCommonFieldDecode(rxSym,preHEChanEst,noiseVar,cfgRx);

        % CRC on HE-SIG-B content channels
        if strcmp(status,'Success')
            fprintf('  HE-SIG-B (common field) CRC pass\n');
        elseif strcmp(status,'ContentChannel1CRCFail')
            fprintf('  ** HE-SIG-B CRC fail for content channel-1\n **');
        elseif strcmp(status,'ContentChannel2CRCFail')
            fprintf('  ** HE-SIG-B CRC fail for content channel-2\n **');
        elseif any(strcmp(status,{'UnknownNumUsersContentChannel1','UnknownNumUsersContentChannel2'}))
            error('  ** Unknown packet length, discard packet\n **');
        else
            % Discard the packet if all HE-SIG-B content channels fail
            error('  ** HE-SIG-B CRC fail **');
        end
        % Update field indices as the number of HE-SIG-B symbols are
        % updated
        ind = wlanFieldIndices(cfgRx);
    end

    % Get complete HE-SIG-B field samples
    rxSIGB = rx(pktOffset+(ind.HESIGB(1):ind.HESIGB(2)),:);
    fprintf(' Decoding HE-SIG-B user field... \n');
    % Decode HE-SIG-B user field
    [failCRC,cfgUsers] = heSIGBUserFieldDecode(rxSIGB,preHEChanEst,noiseVar,cfgRx);

    % CRC on HE-SIG-B users
    if ~all(failCRC)
        fprintf('  HE-SIG-B (user field) CRC pass\n\n');
        numUsers = numel(cfgUsers);
    elseif all(failCRC)
        % Discard the packet if all users fail the CRC
        error('  ** HE-SIG-B CRC fail for all users **');
    else
        fprintf('  ** HE-SIG-B CRC fail for at least one user\n **');
        % Only process users with valid CRC
        numUsers = numel(cfgUsers);
    end

else % HE-SU, HE-EXT-SU
    cfgUsers = {cfgRx};
    numUsers = 1;
end
end