function txNDP = channelSounding(cfg)
% 产生NDP
guardInterval = 0.8;% Guard interval in Microseconds
cfgNDP = wlanHESUConfig('APEPLength',0,'GuardInterval',guardInterval); % No data in an NDP
cfgNDP.ChannelBandwidth = cfg.ChannelBandwidth;
cfgNDP.NumTransmitAntennas = cfg.numTx;
cfgNDP.NumSpaceTimeStreams = cfg.numTx;   
txNDP = wlanWaveformGenerator([],cfgNDP);

% 加入PN序列，正交序列，重复三次左右
soundingSeqMod_1 = zadoffChuSeq(29,255);
soundingSeqMod_2 = zadoffChuSeq(47,255);

% Concatenate multiple sequences to sound the channel periodically.
numSeq = 20;   % Number of transmitted sequences in a WSS period
if cfg.numTx == 1
soundingSeqMod = [soundingSeqMod_1];
txSignal = repmat(soundingSeqMod,numSeq,1);
else
soundingSeqMod = [soundingSeqMod_1, soundingSeqMod_2];
txSignal = repmat(soundingSeqMod,numSeq,1);
end

% with 50 sample padding.
% txNDP = [txNDP; zeros(50,size(txNDP,2))];
txNDP = [txNDP; txSignal; zeros(50,size(txNDP,2))];

end