wlanNonHTOFDMInfo

OFDM information for non-HT transmission

Since R2019a

Syntax

info = wlanNonHTOFDMInfo(field)

info = wlanNonHTOFDMInfo(field,bandwidth)

info = wlanNonHTOFDMInfo(field,cfg)

info = wlanNonHTOFDMInfo(___,OversamplingFactor=osf)

Description

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.

Examples

Get OFDM Information for Non-HT-Data Field

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

info = wlanNonHTOFDMInfo('NonHT-Data');
disp(info);

                 FFTLength: 64
                SampleRate: 20000000
                  CPLength: 16
            NumSubchannels: 1
                  NumTones: 52
    ActiveFrequencyIndices: [52x1 double]
          ActiveFFTIndices: [52x1 double]
               DataIndices: [48x1 double]
              PilotIndices: [4x1 double]

Demodulate Non-HT L-LTF and Get OFDM Information

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,:,:);

Recover PSDU from Non-HT Data Signal

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);
isequal(bits,psdu)

ans = logical
   1

Input Arguments

field — Field for which the function returns OFDM information

'L-LTF' | 'L-SIG' | 'NonHT-Data'

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

bandwidth — Channel bandwidth of transmission

'CBW20' (default) | 'CBW5' | 'CBW10' | 'CBW40' | 'CBW80' | 'CBW160'

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

cfg — Non-HT transmission parameters

wlanNonHTConfig object

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'.

osf — Oversampling factor

1 (default) | scalar greater than or equal to 1

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

info — OFDM information

structure

OFDM information, returned as a structure containing these fields.

Name	Values	Description	Data Types
FFTLength	Positive integer	Length of the fast Fourier transform (FFT)	double
SampleRate	Positive scalar	Sample rate of the waveform	double
CPLength	Positive integer	Cyclic prefix length, in samples	double
NumTones	Nonnegative integer	Number of active subcarriers	double
NumSubchannels	Positive integer	Number of 20 MHz subchannels	double
ActiveFrequencyIndices	Column 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
ActiveFFTIndices	Column vector of integers in the interval [1, FFTLength]	Indices of active subcarriers within the FFT	double
DataIndices	Column vector of integers in the interval [1, NumTones]	Indices of data within the active subcarriers	double
PilotIndices	Column vector of integers in the interval [1, NumTones]	Indices of pilots within the active subcarriers	double

Data Types: struct

Algorithms

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 N_FFT subcarriers comprising N_g guardband subcarriers on either side of N_st occupied bandwidth subcarriers.

Extended Capabilities

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

Version History

Introduced in R2019a