wlanHTOFDMInfo

OFDM information for HT transmission

Syntax

info = wlanHTOFDMInfo(field,cfg)

info = wlanHTOFDMInfo(field,cbw,gi)

info = wlanHTOFDMInfo(field,cbw)

info = wlanHTOFDMInfo(___,OversamplingFactor=osf)

Description

info = wlanHTOFDMInfo(field,cfg) returns info, a structure containing orthogonal frequency-division multiplexing (OFDM) information for the input field in a high-throughput (HT) transmission parameterized by cfg.

info = wlanHTOFDMInfo(field,cbw,gi) returns OFDM information for channel bandwidth cbw and guard interval gi. To return OFDM information for the HT-Data field when the format configuration is unknown, use this syntax.

info = wlanHTOFDMInfo(field,cbw) returns OFDM information for the specified field and channel bandwidth. To return OFDM information for any field other than HT-Data when the format configuration is unknown, use this syntax.

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

Examples

Demodulate HT-LTF and Get OFDM Information

Perform OFDM demodulation on the HT-LTF, then extract the data and pilot subcarriers.

Generate a WLAN waveform for an HT transmission.

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

Obtain the field indices and extract the HT-LTF.

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

Perform OFDM demodulation on the HT-LTF.

sym = wlanHTLTFDemodulate(rx,cfg);

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

info = wlanHTOFDMInfo('HT-LTF',cfg);
data = sym(info.DataIndices,:,:);
pilots =  sym(info.PilotIndices,:,:);

Get OFDM Information for HT-Data Field

Get OFDM information for the HT-Data field.

Specify the channel bandwidth and guard interval duration.

cbw = 'CBW40';
gi = 'Long';

Return and display the OFDM information for the HT-Data field.

info = wlanHTOFDMInfo('HT-Data',cbw,gi);
disp(info);

                 FFTLength: 128
                SampleRate: 40000000
                  CPLength: 32
            NumSubchannels: 2
                  NumTones: 114
    ActiveFrequencyIndices: [114×1 double]
          ActiveFFTIndices: [114×1 double]
               DataIndices: [108×1 double]
              PilotIndices: [6×1 double]

Get OFDM Information for HT L-LTF

Get OFDM information for the L-LTF in a transmission with specified channel bandwidth.

Specify a channel bandwidth of 40 MHz.

cbw = 'CBW40';

Return and display the OFDM information for the L-LTF.

info = wlanHTOFDMInfo('L-LTF',cbw);
disp(info);

                 FFTLength: 128
                SampleRate: 40000000
                  CPLength: [64 0]
            NumSubchannels: 2
                  NumTones: 104
    ActiveFrequencyIndices: [104×1 double]
          ActiveFFTIndices: [104×1 double]
               DataIndices: [96×1 double]
              PilotIndices: [8×1 double]

Input Arguments

field — Field for which to return OFDM information

'L-LTF' | 'L-SIG' | 'HT-SIG' | 'HT-LTF' | 'HT-Data'

Field for which to return 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.

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

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

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

Data Types: char | string

cfg — Transmission parameters

wlanHTConfig object

Transmission parameters, specified as a wlanHTConfig object.

cbw — Channel bandwidth

'CBW20' | 'CBW40'

Channel bandwidth, specified as one of these values.

• 'CBW20' – Channel bandwidth of 20 MHz

• 'CBW40' – Channel bandwidth of 40 MHz

Data Types: char | string

gi — Guard interval duration

'Short' | 'Long'

Guard interval duration, specified as 'Short' or 'Long'.

Data Types: char | string

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, which increases 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 made up of 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