wlanVHTOFDMInfo

OFDM information for VHT transmission

Syntax

info = wlanVHTOFDMInfo(field,cfg)

info = wlanVHTOFDMInfo(field,cbw,gi)

info = wlanVHTOFDMInfo(field,cbw)

info = wlanVHTOFDMInfo(___,OversamplingFactor=osf)

Description

info = wlanVHTOFDMInfo(field,cfg) returns info, a structure containing orthogonal frequency-division multiplexing (OFDM) information for the input field of a very-high-throughput (VHT) transmission parameterized by cfg.

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

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

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

Examples

Demodulate VHT-LTF and Get OFDM Information

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

Generate a WLAN waveform for a VHT transmission.

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

Obtain the field indices and extract the VHT-LTF.

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

Perform OFDM demodulation on the VHT-LTF.

sym = wlanVHTLTFDemodulate(rx,cfg);

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

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

Get OFDM Information for the VHT L-LTF

Get OFDM information for the VHT-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 = wlanVHTOFDMInfo('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]

Get OFDM Information for VHT-Data Field

Get OFDM information for the VHT-Data field in a transmission with specified channel bandwidth and guard interval.

Specify a channel bandwidth of 80 MHz and a short guard interval.

cbw = 'CBW80';
gi = 'Short';

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

info = wlanVHTOFDMInfo('VHT-Data',cbw,gi);
disp(info);

                 FFTLength: 256
                SampleRate: 80000000
                  CPLength: 32
            NumSubchannels: 4
                  NumTones: 242
    ActiveFrequencyIndices: [242×1 double]
          ActiveFFTIndices: [242×1 double]
               DataIndices: [234×1 double]
              PilotIndices: [8×1 double]

Input Arguments

field — Field for which to return OFDM information

'L-LTF' | 'L-SIG' | 'VHT-SIG-A' | 'VHT-SIG-B' | 'VHT-LTF' | 'VHT-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.

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

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

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

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

Data Types: char | string

cfg — Transmission parameters

wlanVHTConfig object

Transmission parameters, specified as a wlanVHTConfig object.

cbw — Channel bandwidth

'CBW20' | 'CBW40' | 'CBW80' | 'CBW160'

Channel bandwidth, specified as one of these values.

• '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

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