wlanHETrackPilotError

R2026b

Track errors using pilot subcarriers of HE waveform

Since R2022a

Syntax

[y,cpe,ae] = wlanHETrackPilotError(x,chanEst,cfg,field)

[y,cpe,ae] = wlanHETrackPilotError(x,chanEst,cfg,field,ruNumber)

[y,cpe,ae] = wlanHETrackPilotError(x,chanEst,cbw,prehefield)

[y,cpe,ae] = wlanHETrackPilotError(___,Name=Value)

Description

[y,cpe,ae] = wlanHETrackPilotError(x,chanEst,cfg,field) tracks errors using the pilot subcarriers of a high-efficiency (HE) WLAN waveform. The function tracks errors using orthogonal frequency-division multiplexing (OFDM) symbols x of the field specified in field and channel estimate chanEst. The function returns the pilot-error-tracked symbols y, common phase error cpe, and amplitude error ae. To track errors in HE single-user (HE SU) waveforms, use this syntax.

[y,cpe,ae] = wlanHETrackPilotError(x,chanEst,cfg,field,ruNumber) also specifies the resource unit (RU) number. This syntax is required to track errors in the HE-LTF or HE-Data fields of HE multi-user (HE MU) waveforms.

[y,cpe,ae] = wlanHETrackPilotError(x,chanEst,cbw,prehefield) returns HE pilot-error-tracked OFDM symbols for pre-HE fields. The pre-HE field is specified in prehefield, and the channel bandwidth is specified in chanbw.

[y,cpe,ae] = wlanHETrackPilotError(___,Name=Value) specifies options using one or more name-value arguments in addition to either input argument combination from the previous syntaxes. For example, TrackAmplitude=true enables pilot amplitude tracking.

Examples

Track Pilot Error in HE SU Waveform

This example shows how to perform pilot phase and amplitude tracking on the L-SIG field of a distorted HE SU waveform.

Generate HE SU Waveform

Configure an HE SU waveform with default transmission parameters and get the nominal sample rate and field indices.

cfgHE = wlanHESUConfig;
cbw = cfgHE.ChannelBandwidth;
fs = wlanSampleRate(cfgHE);
ind = wlanFieldIndices(cfgHE);

Generate the waveform, specifying PSDU bits to transmit.

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

Impair Waveform

Model a step power amplifier droop impairment by applying a step gain change at the start of the L-SIG field.

Specify the droop gain and length.

dbGain = 1; % Droop gain in dB
linearGain = db2mag(dbGain); % Magnitude droop gain
len = double(ind.LSIG(1));

Apply the magnitude droop gain to each time-domain sample of the waveform.

numSamples = size(waveform,1);
droopPerSample = ones(numSamples,1);
droopPerSample(1:len,:) = linearGain*droopPerSample(1:len,:);
rx = droopPerSample.*waveform;

Perform Pilot Amplitude and Phase Tracking

Estimate the channel using the L-LTF.

lltf = rx(ind.LLTF(1):ind.LLTF(2),:);
lltfDemod = wlanHEDemodulate(lltf,"L-LTF",cbw);
chanEst = wlanLLTFChannelEstimate(lltfDemod,cbw);

Demodulate the L-SIG field.

lsig = rx(ind.LSIG(1):ind.LSIG(2),:);
field = "L-SIG";
x = wlanHEDemodulate(lsig,field,cbw);

Track pilot errors using the L-SIG field and display the errors.

[y,cpe,ae] = wlanHETrackPilotError(x, ...
    chanEst,cfgHE,field,TrackAmplitude=true);
disp([cpe ae])

   -0.0000   -1.0000

Input Arguments

x — Received OFDM symbols

complex-valued 3-D array

Received OFDM symbols, specified as a complex-valued array of size N_st-by-N_sym-by-N_r.

• N_st is the number of active subcarriers, which comprises data and pilot subcarriers.

• N_sym is the number of OFDM symbols.

• N_r is the number of receive antennas.

Data Types: single | double
Complex Number Support: Yes

chanEst — Channel estimates

complex-valued 3-D array

Channel estimates at the data and pilot subcarriers or channel estimates at the pilot subcarriers only, specified as a complex-valued array of size N_st-by-N_sts-by-N_r or N_sp-by-N_sts-by-N_r, respectively.

• N_st is the number of occupied subcarriers.

• N_sts is the number of space-time streams.

• N_r is the number of receive antennas.

• N_sp is the number of pilot subcarriers.

Data Types: single | double
Complex Number Support: Yes

cfg — HE transmission parameters

wlanHESUConfig object | wlanHEMUConfig object | wlanHERecoveryConfig object

HE transmission parameters, specified as one of these objects.

• wlanHESUConfig — Set parameters for an HE SU transmission.

• wlanHEMUConfig — Set parameters for an HE MU transmission.

• wlanHERecoveryConfig — Set or recover parameters for an HE SU or HE MU transmission.

field — Field of received OFDM symbols

"L-SIG" | "RL-SIG" | "HE-SIG-A" | "HE-SIG-B" | "HE-LTF" | "HE-Data"

Field of received OFDM symbols, specified as one of these values.

• "L-SIG" — Legacy signal field

• "RL-SIG" — Repeated legacy signal field

• "HE-SIG-A" — HE SIGNAL A field

• "HE-SIG-B" — HE SIGNAL B field

• "HE-LTF"— HE long training field

• "HE-Data" — HE data field

Data Types: char | string

cbw — Channel bandwidth

"CBW20" | "CBW40" | "CBW80" | "CBW160"

Channel bandwidth in MHz, specified as "CBW20","CBW40","CBW80", or "CBW160".

Data Types: char | string

prehefield — Pre-HE field of received OFDM symbols

"L-SIG" | "RL-SIG" | "HE-SIG-A" | "HE-SIG-B"

Pre-HE field of received OFDM symbols, specified as one of these values.

• "L-SIG" — Legacy signal field

• "RL-SIG" — Repeated legacy signal field

• "HE-SIG-A" — HE SIGNAL A field

• "HE-SIG-B" — HE SIGNAL B field

Data Types: char | string

ruNumber — RU number in HE MU transmission

1 (default) | positive integer

RU number in HE MU transmission, 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).

Note

The function requires this input when both of these conditions are satisfied:

• the cfg input is a wlanHEMUConfig object.

• the field input is "HE-Data" or "HE-LTF".

(since R2024a)

Data Types: double

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.

Example: TrackAmplitude=true enables pilot amplitude tracking.

TrackPhase — Pilot phase tracking

1 or true (default) | 0 or false

Enable pilot phase tracking, specified as a numeric or logical 1 (true) or 0 (false). To estimate and correct a common phase offset across all subcarriers and receive antennas, set this property to 1 (true). Otherwise, set this property to 0 (false).

Data Types: logical

TrackAmplitude — Pilot amplitude tracking

0 or false (default) | 1 or true

Enable pilot amplitude tracking, specified as a numeric or logical 1 (true) or 0 (false). To estimate and correct an average amplitude error across all subcarriers for each OFDM symbol and receive antenna, set this property to 1 (true). Otherwise, set this property to 0 (false).

Note

Due to the limitations of the algorithm used, disable pilot amplitude tracking when filtering a waveform through a MIMO fading channel.

Data Types: logical

Output Arguments

y — Pilot-error-tracked OFDM symbols

complex-valued 3-D array

Pilot-error-tracked OFDM symbols, returned as a complex-valued array of size N_st-by-N_sym-by-N_r.

• N_st is the number of occupied subcarriers.

• N_sym is the number of OFDM symbols.

• N_r is the number of receive antennas.

Data Types: single | double
Complex Number Support: Yes

cpe — Common phase error

real-valued row vector

Common phase error, in radians, averaged over all receive antennas, returned as a real-valued row vector of length equal to the number of OFDM symbols. Each element of this vector contains the common phase error for the corresponding OFDM symbol.

Data Types: single | double

ae — Average amplitude error

real-valued matrix

Average amplitude error, in dB, returned as a real-valued matrix of size N_sym-by-N_r.

• N_sym is the number of OFDM symbols.

• N_r is the number of receive antennas.

Each element of this matrix contains the amplitude error for all subcarriers with respect to the estimated received pilots for the corresponding OFDM symbol and receive antenna.

Data Types: single | double

Extended Capabilities

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

Version History

Introduced in R2022a

R2024a: ruNumber required for HE MU pilot error tracking

ruNumber is now a required input when you specify cfg as a wlanHEMUConfig object and field as "HE-LTF" or "HE-Data".