HE/isDataEmpty.m

function flag = isDataEmpty(rx,cfgUI)
chanBW = cfgUI.ChannelBandwidth;
cfgHE=wlanHESUConfig;
cfgHE.NumTransmitAntennas = cfgUI.numTx;
%% Setup Waveform Recovery Parameters
% Perform synchronization with 11ac components
% chanBW = cfg.ChannelBandwidth;
fs = wlanSampleRate(cfgHE);
cfgRx = wlanHERecoveryConfig;
cfgRx.ChannelBandwidth = chanBW;

% Get the field indices for extract fields from the PPDU
% ind = wlanFieldIndices(cfg);
ind = wlanFieldIndices(cfgRx);

% Minimum packet length is 10 OFDM symbols
lstfLength = double(ind.LSTF(2));
minPktLen = lstfLength*5; % Number of samples in L-STF

rxWaveLen = size(rx,1);

%% Front-End Processing
searchOffset = 0; % Offset from start of waveform in samples
while (searchOffset + minPktLen) <= rxWaveLen
    % Packet detection
    coarsePktOffset = wlanPacketDetect(rx,chanBW,searchOffset);

    rxLSTF = rx(coarsePktOffset+(ind.LSTF(1):ind.LSTF(2)), :);
    coarseFreqOffset = wlanCoarseCFOEstimate(rxLSTF,chanBW);
    rx = helperFrequencyOffset(rx,fs,-coarseFreqOffset);
    % 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;
    
    % Extract L-LTF and perform fine frequency offset correction
    rxLLTF = rx(pktOffset+(ind.LLTF(1):ind.LLTF(2)),:);
    fineFreqOff = wlanFineCFOEstimate(rxLLTF,chanBW);
    rx = helperFrequencyOffset(rx,fs,-fineFreqOff);
    
    % Timing synchronization complete: packet detected
    fprintf('Packet detected at index %d\n',pktOffset + 1);

    % Display estimated carrier frequency offset
    cfoCorrection = coarseFreqOffset + fineFreqOff; % Total CFO
    fprintf('Estimated CFO: %5.1f Hz\n\n',cfoCorrection);
    
    break; % Front-end processing complete, stop searching for a packet
    
end

% Scale the waveform based on L-STF power (AGC)
gain = 1./(sqrt(mean(rxLSTF.*conj(rxLSTF))));
rx = rx.*gain;

%% Packet Format Detection

rxLLTF = rx(pktOffset+(ind.LLTF(1):ind.LLTF(2)),:);
lltfDemod = wlanLLTFDemodulate(rxLLTF,chanBW);
lltfChanEst = wlanLLTFChannelEstimate(lltfDemod,chanBW);
noiseVar = helperNoiseEstimate(lltfDemod);

rxSIGA = rx(pktOffset+(ind.LSIG(1):ind.HESIGA(2)),:);
pktFormat = wlanFormatDetect(rxSIGA,lltfChanEst,noiseVar,chanBW);
fprintf('  %s packet detected\n\n',pktFormat);

% Set the packet format in the recovery object and update the field indices
cfgRx.PacketFormat = pktFormat;
ind = wlanFieldIndices(cfgRx);

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

%% L-SIG and RL-SIG Decoding
% 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;


%% HE-SIG-A Decoding
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

%% Interpret Recovered HE-SIG-A bits
cfgRx = interpretHESIGABits(cfgRx,sigaBits);
ind = wlanFieldIndices(cfgRx); % Update field indices
if isempty(ind.HEData)
    flag = true;
else
    flag = false;
end
% %% HE-SIG-B Decoding
% if flag
%     if ~cfgRx.SIGBCompression
%         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