wlanVHTTrackPilotError

Track errors using pilot subcarriers of VHT waveform

Since R2025a

Syntax

[trackedSym,cpe,ae] = wlanVHTTrackPilotError(sym,chEst,cfg,field)

[trackedSym,cpe,ae] = wlanVHTTrackPilotError(___,Name=Value)

Description

[trackedSym,cpe,ae] = wlanVHTTrackPilotError(sym,chEst,cfg,field) tracks errors using the pilot subcarriers of a very high-throughput (VHT) waveform. The function tracks errors using OFDM symbols sym of the field specified in field and channel estimate chEst. The function returns the pilot-error-tracked symbols trackedSym, common phase error cpe, and amplitude error ae.

[trackedSym,cpe,ae] = wlanVHTTrackPilotError(___,Name=Value) specifies additional options using one or more name-value arguments in combination with the previous syntax.

Examples

Track Pilot Amplitude Errors in VHT Waveform Using L-SIG Field

Create a VHT configuration object with default parameters. Generate time-domain waveforms for the legacy long training field (L-LTF) and legacy signal (L-SIG) field.

cfg = wlanVHTConfig;
txLLTF = wlanLLTF(cfg);
txLSIG = wlanLSIG(cfg);

Demodulate the L-LTF and use the demodulated symbols to estimate the channel.

demodLLTF = wlanVHTDemodulate(txLLTF,"L-LTF",cfg);
chEst = wlanLLTFChannelEstimate(demodLLTF,cfg);

Demodulate the L-SIG field. Introduce phase and amplitude errors of 25 degrees and 3 dB, respectively.

demodLSIG = wlanVHTDemodulate(txLSIG,"L-SIG",cfg);
phaseError = 25;
ampError = 3;
sym = demodLSIG*exp(1i*deg2rad(phaseError))*db2mag(ampError);

Pilot-error-track the symbols, returning the phase and amplitude errors.

[trackedSym,cpe,ae] = wlanVHTTrackPilotError(sym,chEst,cfg,"L-SIG",TrackAmplitude=true);

Compare the errors with the values that the function returned.

phaseErrorDiff = rad2deg(cpe) - phaseError

phaseErrorDiff = 
3.5527e-15

ampErrorDiff = ae - ampError

ampErrorDiff = 
4.4409e-16

Input Arguments

sym — Received OFDM symbols

complex-valued 3-D array

Received OFDM symbols, specified as a complex-valued 3-D array. The array has size N_SC-by-N_SYM-by-N_R.

• N_SC is the number of active subcarriers, which comprises data and pilot subcarriers. The number depends on the channel bandwidth.

• N_SYM is the number of OFDM symbols.

• N_R is the number of receive antennas.

Data Types: double | single
Complex Number Support: Yes

chEst — Channel estimate

complex-valued 3-D array

Channel estimate, specified as a complex-valued 3-D array. The channel estimate can be from the data and pilot subcarriers, or from the pilot subcarriers only. The size of the array depends on the value you specify for field and is equal to N_SC-by-N_STS-by-N_R where:

• N_SC is either the total number of data and pilot subcarriers, or the number of pilot subcarriers.

• N_STS is equal to:

  • 1 when field is "L-SIG" or "VHT-SIG-A".

  • The total number of space-time streams when field is "VHT-LTF", "VHT-SIG-B", or "VHT-Data".

• N_R is the number of receive antennas.

Data Types: double | single
Complex Number Support: Yes

cfg — Format configuration

wlanVHTConfig object

Format configuration, specified as a wlanVHTConfig object.

field — Field of received OFDM symbols

"L-SIG" | "VHT-SIG-A" | "VHT-LTF" | "VHT-SIG-B" | "VHT-Data"

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

• "L-SIG" — Legacy signal (L-SIG) field

• "VHT-SIG-A" — VHT signal A (VHT-SIG-A) field

• "VHT-LTF" — VHT long training field (VHT-LTF)

• "VHT-SIG-B" — VHT signal B (VHT-SIG-B) field

• "VHT-Data" — VHT-Data field

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.

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).

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 pilot amplitude tracking algorithm, when filtering a waveform through a MIMO fading channel, disable the TrackAmplitude option.

Output Arguments

trackedSym — Pilot-error-tracked OFDM symbols

complex-valued 3-D array

Pilot-error-tracked OFDM symbols, returned as a complex-valued array of size N_SC-by-N_SYM-by-N_R. The size is equal to the size of the sym input.

If you specify either sym or chEst as single, then trackedSym is single. Otherwise, it is double.

Data Types: double | single
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 with length equal to N_SYM. Each entry of this vector contains the common phase error for the corresponding OFDM symbol.

If you specify either sym or chEst as single, then cpe is single. Otherwise, it is double.

Data Types: double | single

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

If you specify either sym or chEst as single, then ae is single. Otherwise, it is double.

Data Types: double | single

More About

L-SIG

The L-SIG is the third field of the 802.11™ OFDM PLCP legacy preamble. This field is a component of EHT, HE, VHT, HT, and non-HT PPDUs. It consists of 24 bits that contain rate, length, and parity information. The L-SIG field uses BPSK modulation with rate 1/2 binary convolutional coding (BCC).

The L-SIG consists of one OFDM symbol with a duration that varies with channel bandwidth.

Channel Bandwidth (MHz)	Subcarrier Frequency Spacing ΔF (kHz)	Fast Fourier Transform (FFT) Period (TFFT = 1 / ΔF)	Guard Interval (GI) Duration (TGI = TFFT / 4)	L-SIG Duration (TSIGNAL = TGI + TFFT)
20, 40, 80, 160, and 320	312.5	3.2 μs	0.8 μs	4 μs
10	156.25	6.4 μs	1.6 μs	8 μs
5	78.125	12.8 μs	3.2 μs	16 μs

The L-SIG contains packet information for the received configuration.

• Bits 0 through 3 specify the data rate (modulation and coding rate) for the non-HT format.

  Rate (Bits 0–3)	Modulation	Coding Rate (R)	Data Rate (Mb/s)
  			20 MHz Channel Bandwidth	10 MHz Channel Bandwidth	5 MHz Channel Bandwidth
  1101	BPSK	1/2	6	3	1.5
  1111	BPSK	3/4	9	4.5	2.25
  0101	QPSK	1/2	12	6	3
  0111	QPSK	3/4	18	9	4.5
  1001	16-QAM	1/2	24	12	6
  1011	16-QAM	3/4	36	18	9
  0001	64-QAM	2/3	48	24	12
  0011	64-QAM	3/4	54	27	13.5

  For HT and VHT formats, the L-SIG rate bits are set to '1 1 0 1'. Data rate information for HT and VHT formats is signaled in format-specific signaling fields.

• Bit 4 is reserved for future use.

• Bits 5 through 16:

  • For non-HT formats, specify the data length (amount of data transmitted in octets) as described in Table 17-1 and Section 10.27.4 IEEE^® Std 802.11-2020.

  • For HT-mixed formats, specify the transmission time as described in Sections 19.3.9.3.5 and 10.27.4 of IEEE Std 802.11-2020.

  • For VHT formats, specify the transmission time as described in Section 21.3.8.2.4 of IEEE Std 802.11-2020.

• Bit 17 has the even parity of bits 0 through 16.

• Bits 18 through 23 contain all zeros for the signal tail bits.

Note

Signaling fields added for HT (wlanHTSIG) and VHT (wlanVHTSIGA, wlanVHTSIGB) formats provide data rate and configuration information for those formats.

• For the HT-mixed format, Section 19.3.9.4.3 of IEEE Std 802.11-2020 describes HT-SIG bit settings.

• For the VHT format, Sections 21.3.8.3.3 and 21.3.8.3.6 of IEEE Std 802.11-2020 describe bit settings for the VHT-SIG-A and VHT-SIG-B fields, respectively.

VHT-SIG-A

The very high throughput signal A (VHT-SIG-A) field contains information required to interpret VHT format packets. Similar to the non-HT signal (L-SIG) field for the non-HT OFDM format, this field stores the actual rate value, channel coding, guard interval, MIMO scheme, and other configuration details for the VHT format packet. Unlike the HT-SIG field, this field does not store the packet length information. Packet length information is derived from L-SIG and is captured in the VHT-SIG-B field for the VHT format.

For a detailed description of the VHT-SIG-A field, see Section 21.3.8.3.3 of IEEE Std 802.11-2016. The VHT-SIG-A field consists of two symbols: VHT-SIG-A1 and VHT-SIG-A2. These symbols are located between the L-SIG and the VHT-STF portion of the VHT format PPDU.

The VHT-SIG-A field includes the following components. The bit field structures for VHT-SIG-A1 and VHT-SIG-A2 vary for single-user or multi-user transmissions.

• BW — A two-bit field that indicates 0 for 20 MHz, 1 for 40 MHz, 2 for 80 MHz, or 3 for 160 MHz.

• STBC — A bit that indicates the presence of space-time block coding.

• Group ID — A six-bit field that indicates the group and user position assigned to a STA.

• N_STS — A three-bit field for a single user or 4 three-bit fields for a multi-user scenario that indicates the number of space-time streams per user.

• Partial AID — An identifier that combines the association ID and the BSSID.

• TXOP_PS_NOT_ALLOWED — An indicator bit that shows whether client devices are allowed to enter dose state. This bit is set to false when the VHT-SIG-A structure is populated, indicating that the client device is allowed to enter dose state.

• Short GI — A bit that indicates use of the 400 ns guard interval.

• Short GI NSYM Disambiguation — A bit that indicates if an extra symbol is required when the short GI is used.

• SU/MU[0] Coding — A bit field that indicates if convolutional or LDPC coding is used for a single user or for user MU[0] in a multi-user scenario.

• LDPC Extra OFDM Symbol — A bit that indicates if an extra OFDM symbol is required to transmit the data field.

• MCS — A four-bit field.

  • For a single-user scenario, it indicates the modulation and coding scheme used.

  • For a multi-user scenario, it indicates the use of convolutional or LDPC coding and the MCS setting is conveyed in the VHT-SIG-B field.

• Beamformed — An indicator bit set to 1 when a beamforming matrix is applied to the transmission.

• CRC — An eight-bit field used to detect errors in the VHT-SIG-A transmission.

• Tail — A six-bit field used to terminate the convolutional code.

VHT-LTF

The very high throughput long training field (VHT-LTF) is between the VHT-STF and VHT-SIG-B portion of the VHT packet.

Receivers use this field for MIMO channel estimation and pilot subcarrier tracking. The VHT-LTF includes one VHT long training symbol for each spatial stream indicated by the selected modulation and coding scheme (MCS). Each symbol is 4 μs long. The VHT-LTF consists of eight symbols at most.

For a detailed description of the VHT-LTF, see Section 21.3.8.3.5 of IEEE Std 802.11-2016.

VHT-SIG-B

Receivers use the very high throughput signal B (VHT-SIG-B) field in multi-user scenarios to set up the data rate and to fine-tune MIMO reception. The field uses MCS 0 and consists of a single OFDM symbol.

The VHT-SIG-B field is located between the VHT-LTF and the data portion of the VHT format PPDU.

The VHT-SIG-B field contains the actual rate and A-MPDU length value per user. For a detailed description of the VHT-SIG-B field, see Section 21.3.8.3.6 of IEEE Std 802.11-2016. The number of bits in the VHT-SIG-B field varies with the channel bandwidth. The assignment of the bits depends on whether there is a single user or multiple users. For single-user configurations, the same information is available in the L-SIG field, but the VHT-SIG-B field is included for continuity purposes.

Field	VHT MU PPDU Allocation (bits)			VHT SU PPDU Allocation (bits)			Description
	20 MHz	40 MHz	80 MHz, 160 MHz	20 MHz	40 MHz	80 MHz, 160 MHz
VHT-SIG-B	B0–15 (16)	B0–16 (17)	B0–18 (19)	B0–16 (17)	B0–18 (19)	B0–20 (21)	This variable-length field indicates the size of the data payload in four-byte units. The length of the field depends on the channel bandwidth.
VHT-MCS	B16–19 (4)	B17–20 (4)	B19–22 (4)	N/A	N/A	N/A	This four-bit field is included for multi-user scenarios only.
Reserved	N/A	N/A	N/A	B17–19 (3)	B19–20 (2)	B21–22 (2)	All ones
Tail	B20–25 (6)	B21–26 (6)	B23–28 (6)	B20–25 (6)	B21–26 (6)	B23–28 (6)	This six bit field contains all zeros to terminate the convolutional code.
Total number of bits	26	27	29	26	27	29	N/A
Bit field repetition	1	2	4	1	2	4	For 160 MHz, the 80 MHz channel repeats twice.

For a null data packet (NDP), the VHT-SIG-B bits are set according to Table 21-15 of IEEE Std 802.11-2016.

VHT-Data

The VHT-Data field carries one or more frames from the medium access control (MAC) layer. This field follows the VHT-SIG-B field in a VHT PPDU.

For a detailed description of the VHT-Data field, see section 21.3.10 of IEEE Std 802.11-2020. The VHT Data field consists of four subfields.

• Service field — Contains a seven-bit scrambler initialization state, one bit reserved for future considerations, and eight bits for the VHT-SIG-B cyclic redundancy check (CRC) field

• PSDU — Variable-length field containing a PLCP service data unit

• PHY Pad — Variable number of bits passed to the transmitter to create a complete OFDM symbol

• Tail — Bits required to terminate a convolutional code (not required when the transmission uses LDPC channel coding)

References

[1] IEEE Std 802.11-2020 (Revision of IEEE Std 802.11-2016). “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.” IEEE 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™.

Version History

Introduced in R2025a