wlanNonHTOFDMDemodulate

Demodulate fields of non-HT OFDM waveform

Since R2020b

Syntax

sym = wlanNonHTOFDMDemodulate(rx,field,cfg)

sym = wlanNonHTOFDMDemodulate(rx,field,bandwidth)

sym = wlanNonHTOFDMDemodulate(___,Name=Value)

Description

sym = wlanNonHTOFDMDemodulate(rx,field,cfg) recovers a frequency-domain signal by orthogonal frequency-division multiplexing (OFDM) demodulating non-high-throughput (non-HT) time-domain signal rx. The function demodulates rx by using non-HT transmission parameters cfg and signal field value field.

sym = wlanNonHTOFDMDemodulate(rx,field,bandwidth) specifies the channel bandwidth of the transmission.

sym = wlanNonHTOFDMDemodulate(___,Name=Value) specifies options using one or more name-value arguments in addition to any combination of input arguments from the previous syntaxes.

Examples

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

Recover Bandwidth Signaling from Initial Scrambler State

Configure and generate a non-HT Data signal with a channel bandwidth of 160 MHz and dynamic bandwidth operation.

bandwidth = 'CBW160';
cfg = wlanNonHTConfig(ChannelBandwidth=bandwidth,PSDULength=1, ...
    SignalChannelBandwidth=true,BandwidthOperation='Dynamic');
bits = randi([0 1],8*cfg.PSDULength,1,'int8');
[range,~] = scramblerRange(cfg);
scramInit = randi(range);
y = wlanNonHTData(bits,cfg,scramInit);

Transmit the waveform through an AWGN channel with an SNR of 50.

snr = 50;
noiseVarEst = 10^(-snr/10);
rx = awgn(y,snr);

Recover the frequency-domain signal by OFDM-demodulating the non-HT Data signal, specifying an OFDM symbol sampling offset.

field = 'NonHT-Data';
symOffset = 0.5;
sym = wlanNonHTOFDMDemodulate(rx,field,bandwidth,OFDMSymbolOffset=symOffset);

Extract the data subcarriers.

info = wlanNonHTOFDMInfo(field,bandwidth);
sym = sym(info.DataIndices,:);

Recover the first 20 MHz subchannel of the PSDU, enhancing the demapping of the OFDM subcarriers by specifying channel state information. Confirm that the received and transmitted PSDUs match.

csi = ones(48,1);
[psdu,scramInit] = wlanNonHTDataBitRecover(sym(1:48,:),noiseVarEst,csi,cfg);
isequal(bits,psdu)

ans = logical
   1

Recover and display bandwidth signaling by interpreting the scrambler state.

[bandwidth,dyn] = wlanInterpretScramblerState(scramInit)

bandwidth = 
'CBW160'

dyn = logical
   1

Input Arguments

rx — Received time-domain signal

complex-valued matrix

Received time-domain signal, specified as a complex-valued matrix of size N_s-by-N_r.

• N_s is the number of time-domain samples. If N_s is not an integer multiple of the OFDM symbol length, L_s, for the specified field, then the function ignores the remaining mod(Ns,Ls) symbols.

• N_r is the number of receive antennas.

Data Types: single | double
Complex Number Support: Yes

field — Field to be demodulated

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

Field to be demodulated, specified as one of these values.

• 'L-LTF' — Demodulate legacy long training field (L-LTF).

• 'L-SIG' — Demodulate the legacy signaling (L-SIG) field.

• 'NonHT-Data' — Demodulate the non-HT Data field.

Data Types: char | string

cfg — Non-HT transmission parameters

wlanNonHTConfig object

Non-HT transmission parameters, specified as a wlanNonHTConfig object.

bandwidth — Channel bandwidth

'CBW5' | 'CBW10' | 'CBW20' | 'CBW40' | 'CBW80' | 'CBW160'

Channel bandwidth, 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

• 'CBW80' — Channel bandwidth of 80 MHz

• 'CBW160' — Channel bandwidth of 160 MHz

Data Types: char | string

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: symOffset=0.5

OFDMSymbolOffset — OFDM symbol sampling offset

0.75 (default) | scalar in the interval [0, 1]

OFDM symbol sampling offset, as a fraction of the cyclic prefix length, specified as a scalar in the interval [0, 1].

The value that you specify indicates the start location for OFDM demodulation relative to the beginning of the cyclic prefix.

Example: 0.45

Data Types: double

OversamplingFactor — Oversampling factor

1 (default) | scalar greater than 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. For more information, see FFT-Based Oversampling.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

sym — Demodulated frequency-domain signal

complex-valued array

Demodulated frequency-domain signal, returned as a complex-valued array of size N_sc-by-N_sym-by-N_r.

• N_sc is the number of active occupied subcarriers in the demodulated field.

• N_sym is the number of OFDM symbols.

• N_r is the number of receive antennas.

Data Types: single | double
Complex Number Support: Yes

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 R2020b

R2024a: FFT-based oversampling

The function now supports FFT-based oversampling. To specify an oversampling factor, use the OversamplingFactor name-value argument.

R2023b: Single precision support

This function supports single-precision values for its numeric input arguments.