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OFDM information for non-HT transmission



info = wlanNonHTOFDMInfo(field) returns orthogonal frequency-division multiplexing (OFDM) information for the specified field of a non-high-throughput (non-HT) transmission.


info = wlanNonHTOFDMInfo(field,bandwidth) specifies the channel bandwidth of the non-HT transmission.


info = wlanNonHTOFDMInfo(field,cfg) specifies non-HT transmission parameters.

info = wlanNonHTOFDMInfo(___,OversamplingFactor=osf) returns OFDM information for the specified oversampling factor. For more information about oversampling, see FFT-Based Oversampling.


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Get and display the OFDM information for the non-HT-Data field.

info = wlanNonHTOFDMInfo('NonHT-Data');
                 FFTLength: 64
                SampleRate: 20000000
                  CPLength: 16
            NumSubchannels: 1
                  NumTones: 52
    ActiveFrequencyIndices: [52x1 double]
          ActiveFFTIndices: [52x1 double]
               DataIndices: [48x1 double]
              PilotIndices: [4x1 double]

OFDM demodulate the L-LTF in a non-HT transmission, then extract the data and pilot subcarriers.

Generate a WLAN waveform for a non-HT transmission.

cfg = wlanNonHTConfig;
bits = [1; 0; 0; 1];
waveform = wlanWaveformGenerator(bits,cfg);

Obtain the field indices and extract the L-LTF.

ind = wlanFieldIndices(cfg);
rx = waveform(ind.LLTF(1):ind.LLTF(2),:);

Perform OFDM demodulation on the L-LTF.

sym = wlanLLTFDemodulate(rx,cfg);

Get the OFDM information, then extract the data and pilot subcarriers.

bandwidth = cfg.ChannelBandwidth;
info = wlanNonHTOFDMInfo('L-LTF',bandwidth);
data = sym(info.DataIndices,:,:);
pilots = sym(info.PilotIndices,:,:);

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

Input Arguments

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Field for which the function returns OFDM information, specified as one of these values.

  • 'L-LTF' – Return OFDM information for the legacy long training field (L-LTF).

  • 'L-SIG' – Return OFDM information for the legacy signal (L-SIG) field.

  • 'NonHT-Data' – Return OFDM information for the non-HT Data field.

Data Types: char | string

Channel bandwidth of PPDU transmission, 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 for non-HT duplicate

  • 'CBW80' — Channel bandwidth of 80 MHz for non-HT duplicate

  • 'CBW160' — Channel bandwidth of 160 MHz for non-HT duplicate

Data Types: char | string

Non-HT transmission parameters, specified as a wlanNonHTConfig object. Because this function supports only OFDM modulation, you must set the Modulation property of this input to 'OFDM'.

Oversampling factor, specified as a scalar greater than or equal to 1. The oversampled cyclic prefix length must be an integer number of samples.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

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OFDM information, returned as a structure containing these fields.

NameValuesDescriptionData Types
FFTLengthPositive integerLength of the fast Fourier transform (FFT)double
SampleRatePositive scalarSample rate of the waveformdouble
CPLengthPositive integer

Cyclic prefix length, in samples

NumTonesNonnegative integer

Number of active subcarriers

NumSubchannelsPositive integerNumber of 20 MHz subchannelsdouble
ActiveFrequencyIndicesColumn vector of integers in the interval [–FFTLength/2, (FFTLength/2 – 1)]Indices of active subcarriers. Each element of this field is the index of an active subcarrier, such that the direct current (DC) or null subcarrier is at the center of the frequency band.double
ActiveFFTIndicesColumn vector of integers in the interval [1, FFTLength]Indices of active subcarriers within the FFTdouble
DataIndicesColumn vector of integers in the interval [1, NumTones]Indices of data within the active subcarriersdouble
PilotIndicesColumn vector of integers in the interval [1, NumTones]Indices of pilots within the active subcarriersdouble

Data Types: struct


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FFT-Based Oversampling

An oversampled signal is a signal sampled at a frequency that is higher than the Nyquist rate. WLAN signals maximize occupied bandwidth by using small guardbands, which can pose problems for anti-imaging and anti-aliasing filters. Oversampling increases the guardband width relative to the total signal bandwidth, thereby increasing the number of samples in the signal.

This function performs oversampling by using a larger IFFT and zero pad when generating an OFDM waveform. This diagram shows the oversampling process for an OFDM waveform with NFFT subcarriers comprising Ng guardband subcarriers on either side of Nst occupied bandwidth subcarriers.

FFT-based oversampling

Extended Capabilities

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

Version History

Introduced in R2019a