Main Content


Recover VHT-SIG-B information bits



recBits = wlanVHTSIGBRecover(rxSig,chEst,noiseVarEst,cbw) returns the recovered information bits from the VHT-SIG-B1 field for a single-user transmission. Inputs include the received VHT-SIG-B field, the channel estimate, the noise variance estimate, and the channel bandwidth.

recBits = wlanVHTSIGBRecover(rxSig,chEst,noiseVarEst,cbw,userNumber,numSTS) returns the recovered information bits of a multiuser transmission for the user of interest, userNumber, and the number of space-time streams, numSTS.


recBits = wlanVHTSIGBRecover(___,Name,Value) specifies algorithm parameters by using one or more name-value pair arguments.


[recBits,eqSym] = wlanVHTSIGBRecover(___) returns the equalized symbols, eqSym, using the arguments from previous syntaxes.


[recBits,eqSym,cpe] = wlanVHTSIGBRecover(___) returns the common phase error, cpe.


collapse all

Recover VHT-SIG-B bits in a perfect channel having 80 MHz channel bandwidth, one space-time stream, and one receive antenna.

Create a wlanVHTConfig object having a channel bandwidth of 80 MHz. Using the object, create a VHT-SIG-B waveform.

cfg = wlanVHTConfig('ChannelBandwidth','CBW80');
[txSig,txBits] = wlanVHTSIGB(cfg);

For a channel bandwidth of 80 MHz, there are 242 occupied subcarriers. The channel estimate array dimensions for this example must be [Nst,Nsts,Nr] = [242,1,1]. The example assumes a perfect channel and one receive antenna. Therefore, specify the channel estimate as a column vector of ones and the noise variance estimate as zero.

chEst = ones(242,1);
noiseVarEst = 0;

Recover the VHT-SIG-B. Verify that the received information bits are identical to the transmitted bits.

rxBits = wlanVHTSIGBRecover(txSig,chEst,noiseVarEst,'CBW80');
ans = logical

Recover the VHT-SIG-B field using a zero-forcing equalizer in an AWGN channel with a channel bandwidth of 160 MHz, one space-time stream, and one receive antenna.

Create a wlanVHTConfig object, specifying a channel bandwidth of 160 MHz. Using the object, create a VHT-SIG-B waveform.

cfg = wlanVHTConfig('ChannelBandwidth','CBW160');
[txSig,txBits] = wlanVHTSIGB(cfg);

Pass the transmitted VHT-SIG-B through an AWGN channel.

noiseVarEst = 0.1;
awgnChan = comm.AWGNChannel('NoiseMethod','Variance','Variance',noiseVarEst);
rxSig = awgnChan(txSig);

Recover the VHT-SIG-B field, specifying zero-forcing equalization. Verify that the received information has no bit errors.

chEst = ones(484,1);
recBits = wlanVHTSIGBRecover(rxSig,chEst,noiseVarEst,'CBW160','EqualizationMethod','ZF');
numErr = biterr(txBits,recBits)
numErr = 0

Recover VHT-SIG-B in a 2x2 MIMO channel for an SNR=10 dB and a receiver that has a 9 dB noise figure. Confirm that the information bits are recovered correctly.

Set the channel bandwidth and the corresponding sample rate.

cbw = 'CBW20';
fs = 20e6;

Create a VHT configuration object with 20 MHz bandwidth and two transmission paths. Generate the L-LTF and VHT-SIG-B waveforms.

vht = wlanVHTConfig('ChannelBandwidth',cbw,'NumTransmitAntennas',2, ...

txVHTLTF = wlanVHTLTF(vht);
[txVHTSIGB,txVHTSIGBBits] = wlanVHTSIGB(vht);

Pass the VHT-LTF and VHT-SIG-B waveforms through a 2x2 TGac channel.

tgacChan = wlanTGacChannel('NumTransmitAntennas',2, ...
    'NumReceiveAntennas',2, 'ChannelBandwidth',cbw,'SampleRate',fs);
rxVHTLTF = tgacChan(txVHTLTF);
rxVHTSIGB = tgacChan(txVHTSIGB);

Add white noise for an SNR = 10dB.

chNoise = comm.AWGNChannel('NoiseMethod','Signal to noise ratio (SNR)',...

rxVHTLTF = chNoise(rxVHTLTF);
rxVHTSIGB = chNoise(rxVHTSIGB);

Add additional white noise corresponding to a receiver with a 9 dB noise figure. The noise variance is equal to k*T*B*F, where k is Boltzmann's constant, T is the ambient temperature, B is the channel bandwidth (sample rate), and F is the receiver noise figure.

nVar = 10^((-228.6+10*log10(290)+10*log10(fs)+9)/10);
rxNoise = comm.AWGNChannel('NoiseMethod','Variance','Variance',nVar);

rxVHTLTF = rxNoise(rxVHTLTF);
rxVHTSIGB = rxNoise(rxVHTSIGB);

Demodulate the VHT-LTF signal and use it to generate a channel estimate.

demodVHTLTF = wlanVHTLTFDemodulate(rxVHTLTF,vht);
chEst = wlanVHTLTFChannelEstimate(demodVHTLTF,vht);

Recover the VHT-SIG-B information bits. Display the scatter plot of the equalized symbols.

[recVHTSIGBBits,eqSym,cpe] = wlanVHTSIGBRecover(rxVHTSIGB,chEst,nVar,cbw);

Display the common phase error.

cpe = 0.0485

Determine the number of errors between the transmitted and received VHT-SIG-B information bits.

numErr = biterr(txVHTSIGBBits,recVHTSIGBBits)
numErr = 0

Input Arguments

collapse all

Received VHT-SIG-B field, specified as an NS-by-NR matrix. NS is the number of samples and increases with channel bandwidth.

Channel BandwidthNS

NR is the number of receive antennas.

Data Types: double | single
Complex Number Support: Yes

Channel estimate, specified as an NST-by-NSTS-by-NR array. NST is the number of occupied subcarriers. NSTS is the number of space-time streams. For multiuser transmissions, NSTS is the total number of space-time streams for all users. NR is the number of receive antennas.

NST increases with channel bandwidth.

ChannelBandwidthNumber of Occupied Subcarriers (NST)Number of Data Subcarriers (NSD)Number of Pilot Subcarriers (NSP)

The channel estimate is based on the VHT-LTF.

Data Types: double | single

Noise variance estimate, specified as a nonnegative scalar.

Data Types: double | single

Channel bandwidth, specified as 'CBW20', 'CBW40', 'CBW80', or 'CBW160'.

Data Types: char | string

Number of the user in a multiuser transmission, specified as an integer having a value from 1 to NUsers. NUsers is the total number of users.

Number of space-time streams in a multiuser transmission, specified as a vector. The number of space-time streams is a 1-by-NUsers vector of integers from 1 to 4, where NUsers is an integer from 1 to 4.

Example: [1 3 2] is the number of space-time streams for each user.


The sum of the space-time stream vector elements must not exceed eight.

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: 'PilotPhaseTracking','None' disables pilot phase tracking.

OFDM symbol sampling offset represented as a fraction of the cyclic prefix (CP) length, specified as the name-value pair consisting of 'OFDMSymbolOffset' and a scalar in the interval [0, 1]. The value you specify indicates the start location for OFDM demodulation relative to the beginning of the CP. The value 0 represents the start of the CP, and the value 1 represents the end of the CP.

Different values of the OFDMSymbolOffset argument

Data Types: double

Equalization method, specified as one of these values.

  • 'MMSE' — The receiver uses a minimum mean-square error equalizer.

  • 'ZF' — The receiver uses a zero-forcing equalizer.

When the received signal has multiple receive antennas, the function exploits receiver diversity during equalization. When the number of transmitted space-time streams is one and you specify this argument as 'ZF', the function performs maximal-ratio combining.

Data Types: char | string

Pilot phase tracking, specified as the name-value pair consisting of 'PilotPhaseTracking' and one of these values.

  • 'PreEQ' — Enable pilot phase tracking, which the function performs before any equalization operation.

  • 'None' — Disable pilot phase tracking.

Data Types: char | string

Output Arguments

collapse all

Recovered VHT-SIG-B information bits, returned as an Nb-by-1 column vector. Nb is the number of recovered VHT-SIG-B information bits and increases with the channel bandwidth. The output is for a single user as determined by userNumber.

The number of output bits is proportional to the channel bandwidth.


See VHT-SIG-B for information about the meaning of each bit in the field.

Equalized symbols, returned as an NSD-by-1 column vector. NSD is the number of data subcarriers.

NSD increases with the channel bandwidth.


Common phase error in radians, returned as a scalar.

More About

collapse all


Receivers use the very high throughput signal B field (VHT-SIG-B) 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 in a VHT packet

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 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.


VHT MU PPDU Allocation (bits)

VHT SU PPDU Allocation (bits)



20 MHz

40 MHz

80 MHz, 160 MHz

20 MHz

40 MHz

80 MHz, 160 MHz



B0-15 (16)

B0-16 (17)

B0-18 (19)

B0-16 (17)

B0-18 (19)

B0-20 (21)

A variable-length field that indicates the size of the data payload in four-byte units. The length of the field depends on the channel bandwidth.


B16-19 (4)

B17-20 (4)

B19-22 (4)




A four-bit field that is included for multiuser scenarios only.





B17–19 (3)

B19-20 (2)

B21-22 (2)

All ones


B20-25 (6)

B21-26 (6)

B23-28 (6)

B20-25 (6)

B21-26 (6)

B23-28 (6)

Six zero-bits used to terminate the convolutional code.

Total # bits








Bit field repetition




For 160 MHz, the 80 MHz channel is repeated twice.




For 160 MHz, the 80 MHz channel is repeated 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.


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

The VHT-LTF in the VHT packet

It is used 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. A maximum of eight symbols are permitted in the VHT-LTF.

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


PLCP protocol data unit

The PPDU is the complete PLCP frame, including PLCP headers, MAC headers, the MAC data field, and the MAC and PLCP trailers.


collapse all

VHT-SIG-B Recovery

The VHT-SIG-B field consists of one symbol and resides between the VHT-LTF field and the data portion of the packet structure for the VHT format PPDUs.

Structure of VHT format PPDU

For single-user packets, you can recover the length information from the L-SIG and VHT-SIG-A field information. Therefore, it is not strictly required for the receiver to decode the VHT-SIG-B field. For multiuser transmissions, recovering the VHT-SIG-B field provides packet length and MCS information for each user.

Process of recovering bits from VHT-SIG-B waveform

For VHT-SIG-B details, refer to IEEE Std 802.11ac™-2013 [1], Section, and Perahia [2], Section


[1] IEEE Std 802.11ac™-2013 IEEE Standard for Information technology — Telecommunications and information exchange between systems — Local and metropolitan area networks — Specific requirements — Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications — Amendment 4: Enhancements for Very High Throughput for Operation in Bands below 6 GHz.

[2] Perahia, E., and R. Stacey. Next Generation Wireless LANs: 802.11n and 802.11ac. 2nd Edition, United Kingdom: Cambridge University Press, 2013.

Extended Capabilities

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

Version History

Introduced in R2015b

expand all

1 IEEE Std 802.11ac™-2013 Adapted and reprinted with permission from IEEE. Copyright IEEE 2013. All rights reserved.