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Demodulate fields of non-HT OFDM waveform



sym = wlanNonHTOFDMDemodulate(rx,field,cfg) recovers a frequency-domain signal by orthogonal frequency-division multiplexing (OFDM) demodulating non-high-throughput (non-HT) time-domain signal rx. The function demodulates rx by using non-HT transmission parameters cfg and signal field value field.

sym = wlanNonHTOFDMDemodulate(rx,field,bandwidth) specifies the channel bandwidth of the transmission.


sym = wlanNonHTOFDMDemodulate(___,'OFDMSymbolOffset',symOffset) specifies the OFDM symbol sampling offset as a fraction of the cyclic prefix length in addition to any combination of input arguments from the previous syntaxes..


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Configure and generate a non-HT time-domain waveform.

cfg = wlanNonHTConfig('MCS',4);
bits = randi([0 1],8*cfg.PSDULength,1,'int8');
waveform = wlanWaveformGenerator(bits,cfg);

Transmit the waveform through an additive white Gaussian noise (AWGN) channel with a signal-to-noise ratio (SNR) of 30.

snr = 30;
rxWaveform = awgn(waveform,snr);

Extract the non-HT Data field from the received waveform.

field = 'NonHT-Data';
ind = wlanFieldIndices(cfg,field);
rx = rxWaveform(ind(1):ind(2),:);

Recover the frequency-domain signal by OFDM demodulating the time-domain data signal.

sym = wlanNonHTOFDMDemodulate(rx,field,cfg);

Extract the data subcarriers from the demodulated signal.

info = wlanNonHTOFDMInfo(field,cfg);
sym = sym(info.DataIndices,:,:);

Recover the PSDU and confirm that it matches the transmitted PSDU.

noiseVarEst = 10^(-snr/10);
psdu = wlanNonHTDataBitRecover(sym,noiseVarEst,cfg);
ans = logical

Configure and generate a non-HT Data signal with a channel bandwidth of 160 MHz and dynamic bandwidth operation.

bandwidth = 'CBW160';
cfg = wlanNonHTConfig('ChannelBandwidth',bandwidth,'PSDULength',1, ...
bits = randi([0 1],8*cfg.PSDULength,1,'int8');
[range,~] = scramblerRange(cfg);
scramInit = randi(range);
y = wlanNonHTData(bits,cfg,scramInit);

Transmit the waveform through an AWGN channel with an SNR of 50.

snr = 50;
noiseVarEst = 10^(-snr/10);
rx = awgn(y,snr);

Recover the frequency-domain signal by OFDM demodulating the non-HT Data signal, specifying an OFDM symbol sampling offset.

field = 'NonHT-Data';
symOffset = 0.5;
sym = wlanNonHTOFDMDemodulate(rx,field,bandwidth,'OFDMSymbolOffset',symOffset);

Extract the data subcarriers.

info = wlanNonHTOFDMInfo(field,bandwidth);
sym = sym(info.DataIndices,:);

Recover the first 20 MHz subchannel of the PSDU, enhancing the demapping of the OFDM subcarriers by specifying channel state information. Confirm that the received and transmitted PSDUs match.

csi = ones(48,1);
[psdu,scramInit] = wlanNonHTDataBitRecover(sym(1:48,:),noiseVarEst,csi,cfg);
ans = logical

Recover and display bandwidth signaling by interpreting the scrambler state.

[bandwidth,dyn] = wlanInterpretScramblerState(scramInit)
bandwidth = 
dyn = logical

Input Arguments

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Received time-domain signal, specified as a complex-valued matrix of size Ns-by-Nr.

  • Ns is the number of time-domain samples. If Ns is not an integer multiple of the OFDM symbol length, Ls, for the specified field,then the function ignores the remaining mod(Ns,Ls) symbols.

  • Nr is the number of receive antennas.

Data Types: double
Complex Number Support: Yes

Field to be demodulated, specified as one of these values.

  • 'L-LTF' – Demodulate legacy long training field (L-LTF).

  • 'L-SIG' – Demodulate the legacy signaling (L-SIG) field.

  • 'NonHT-Data' – Demodulate the non-HT Data field.

Data Types: char | string

Non-HT transmission parameters, specified as a wlanNonHTConfig object.

Channel bandwidth, specified as one of these values.

  • 'CBW5' – Channel bandwidth of 5 MHz

  • 'CBW10' – Channel bandwidth of 10 MHz

  • 'CBW20' – Channel bandwidth of 20 MHz

  • 'CBW40' – Channel bandwidth of 40 MHz

  • 'CBW80' – Channel bandwidth of 80 MHz

  • 'CBW160' – Channel bandwidth of 160 MHz

Data Types: char | string

OFDM symbol sampling offset, as a fraction of the cyclic prefix length, specified as a scalar in the interval [0, 1].

The value that you specify indicates the start location for OFDM demodulation relative to the beginning of the cyclic prefix.

Example: 0.45

Data Types: double

Output Arguments

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Demodulated frequency-domain signal, returned as a complex-valued array of size Nsc-by-Nsym-by-Nr.

  • Nsc is the number of active occupied subcarriers in the demodulated field.

  • Nsym is the number of OFDM symbols.

  • Nr is the number of receive antennas.

Data Types: double
Complex Number Support: Yes

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Introduced in R2020b