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wlanVHTOFDMInfo

OFDM information for VHT transmission

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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.

example

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.

example

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.

example

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

Examples

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Open Live Script

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,:,:);
Open Live Script

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: [104x1 double]
          ActiveFFTIndices: [104x1 double]
               DataIndices: [96x1 double]
              PilotIndices: [8x1 double]
Open Live Script

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: [242x1 double]
          ActiveFFTIndices: [242x1 double]
               DataIndices: [234x1 double]
              PilotIndices: [8x1 double]

Input Arguments

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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

Transmission parameters, specified as a wlanVHTConfig object.

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

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

Data Types: char | string

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

double
NumTonesNonnegative integer

Number of active subcarriers

double
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

Algorithms

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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, 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 NFFT subcarriers made up of 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

See Also

Functions

Objects