wlanHEOFDMInfo

OFDM information for HE transmission

Syntax

info = wlanHEOFDMInfo(field,cfg)

info = wlanHEOFDMInfo(field,cfg,ruNumber)

info = wlanHEOFDMInfo(field,cbw,hegi,ru)

info = wlanHEOFDMInfo(field,cbw)

info = wlanHEOFDMInfo(___,OversamplingFactor=osf)

Description

info = wlanHEOFDMInfo(field,cfg) returns info, a structure containing orthogonal frequency-division multiplexing (OFDM) information for the input field in a high-efficiency (HE) transmission parameterized by configuration object cfg.

info = wlanHEOFDMInfo(field,cfg,ruNumber) returns OFDM information for the resource unit (RU) of interest determined by its number ruNumber, when you specify cfg as an HE multi-user (HE MU) configuration. To return OFDM information for either the HE-Data field or the HE long training field (HE-LTF) in an HE MU transmission, use this syntax.

info = wlanHEOFDMInfo(field,cbw,hegi,ru) returns OFDM information for channel bandwidth cbw, guard interval hegi, and RU of interest determined by its size and index specified in ru. If you do not specify ru, then wlanHEOFDMInfo returns information assuming a full band configuration. To return OFDM information for either the HE-Data field or the HE-LTF when the PHY format configuration is unknown, use this syntax.

info = wlanHEOFDMInfo(field,cbw) returns OFDM information for the specified field and channel bandwidth. To return OFDM information for one of the L-LTF, L-SIG, RL-SIG, HE-SIG-A, or HE-SIG-B fields when the PHY format configuration is unknown, use this syntax.

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

Examples

Demodulate HE-SIG-A Field and Get OFDM Information

Perform OFDM demodulation on the HE-SIG-A field and extract the data and pilot subcarriers.

Generate a WLAN waveform for an HE SU transmission.

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

Obtain the field indices and extract the HE-SIG-A field.

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

Perform OFDM demodulation on the HE-SIG-A field.

sym = wlanHEDemodulate(rx,'HE-SIG-A',cfg);

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

info = wlanHEOFDMInfo('HE-SIG-A',cfg);
data = sym(info.DataIndices,:,:);
pilots =  sym(info.PilotIndices,:,:);

Get OFDM Information for RUs in HE MU Waveform

Get OFDM information for each RU in an HE MU waveform.

Create a WLAN HE-MU-format configuration object with the allocation index set to 16.

AllocationIndex = 16;
cfg = wlanHEMUConfig(AllocationIndex);

Get the OFDM information pertaining to the HE-Data field for each RU and extract the number of active subcarriers in each case.

NumTones =  zeros(numel(cfg.RU),1);
for ruNumber = 1:numel(cfg.RU)
    info = wlanHEOFDMInfo('HE-Data',cfg,ruNumber);
    NumTones(ruNumber) = info.NumTones;
end

Display the number of active subcarriers for each RU.

disp(NumTones');

    52    52   106

Get OFDM Information for L-LTF

Get OFDM information for the legacy long training field (L-LTF) for a specified channel bandwidth.

Specify a channel bandwidth of 40 MHz.

cbw = 'CBW40';

Get the OFDM information for the L-LTF and display the fast Fourier transform (FFT) length.

info = wlanHEOFDMInfo('L-LTF',cbw);
disp(info.FFTLength);

   128

Input Arguments

field — Field for which to return OFDM information

'L-LTF' | 'L-SIG' | 'RL-SIG' | 'HE-SIG-A' | 'HE-SIG-B' | 'HE-LTF' | 'HE-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.

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

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

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

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

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

Data Types: char | string

cfg — PHY format configuration

wlanHESUConfig object | wlanHEMUConfig object | wlanHETBConfig object | wlanHERecoveryConfig object

Physical layer (PHY) format configuration, specified as an object of type wlanHESUConfig, wlanHEMUConfig, wlanHETBConfig, or wlanHERecoveryConfig.

When you specify this input as a wlanHETBConfig object with the FeedbackNDP property set to 1 (true), the function interleaves the symbols for active and complementary tone sets for the value of the RUToneSetIndex property in accordance with Table 27-30 of [1].

ruNumber — Number of RU of interest

positive integer

Number of the RU of interest, specified as a positive integer. The RU number specifies the location of the RU within the channel. For example, consider an 80-MHz transmission with two 242-tone RUs and one 484-tone RU, in order of absolute frequency. For this allocation:

• RU number 1 corresponds to the 242-tone RU in the 20-MHz subchannel at the lowest absolute frequency (size 242, index 1).

• RU number 2 corresponds to the 242-tone RU in the 20-MHz subchannel at the next lowest absolute frequency (size 242, index 2).

• RU number 3 corresponds to the 484-tone RU in the 40-MHz subchannel at the highest absolute frequency (size 484, index 2).

Data Types: double

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

hegi — Guard interval duration

0.8 | 1.6 | 3.2

Guard interval duration, in microseconds, specified as 0.8, 1.6, or 3.2.

Data Types: double

ru — RU size and index

1-by-2 vector of positive scalars

RU size and index, specified as a 1-by-2 vector of positive scalars. Specify ru in the form [size,index], where size must be 26, 52, 106, 242, 484, 996, or 1992 in accordance with the specified channel bandwidth. For example, an 80-MHz transmission has four possible 242-tone RUs (one for each 20-MHz subchannel). RU number 242-1 (size = 242 and index = 1) is the lowest absolute frequency within the 80-MHz channel. RU number 242-4 is the highest absolute frequency.

Data Types: double

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
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 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.

References

[1] IEEE P802.11ax™/D4.1. “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 1: Enhancements for High Efficiency WLAN.” Draft Standard for Information technology — Telecommunications and information exchange between systems. Local and metropolitan area networks — Specific requirements.

Extended Capabilities

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