Recover VHT-SIG-B information bits
Recover VHT-SIG-B bits in a perfect channel having 80 MHz channel bandwidth, one space-time stream, and one receive antenna.
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'); isequal(txBits,rxBits)
ans = logical 1
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.
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, ... 'NumSpaceTimeStreams',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)',... 'SNR',10); 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); scatterplot(eqSym)
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
rxSig— Received VHT-SIG-B
Received VHT-SIG-B field, specified as an NS-by-NR matrix. NS is the number of samples and increases with channel bandwidth.
NR is the number of receive antennas.
Complex Number Support: Yes
chEst— Channel estimate
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.
|Number of Occupied Subcarriers (NST)||Number of Data Subcarriers (NSD)||Number of Pilot Subcarriers (NSP)|
The channel estimate is based on the VHT-LTF.
noiseVarEst— Noise variance estimate
Noise variance estimate, specified as a nonnegative scalar.
cbw— Channel bandwidth
Channel bandwidth, specified as
userNumber— Number of the user
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.
numSTS— Number of space-time streams
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.
[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.
comma-separated pairs of
the argument name and
Value is the corresponding value.
Name must appear inside quotes. You can specify several name and value
pair arguments in any order as
'PilotPhaseTracking','None'disables pilot phase tracking.
recBits— Recovered VHT-SIG information
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
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.
eqSym— Equalized symbols
Equalized symbols, returned as an NSD-by-1 column vector. NSD is the number of data subcarriers.
NSD increases with the channel bandwidth.
cpe— Common phase error
Common phase error in radians, returned as a scalar.
The very high throughput signal B field (VHT-SIG-B) is used for multiuser scenario to set up the data rate and to fine-tune MIMO reception. It is modulated using MCS 0 and is transmitted in a single OFDM symbol.
The VHT-SIG-B field consists of a single OFDM symbol located between the VHT-LTF and the data portion of the VHT format PPDU.
The very high throughput signal B (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 184.108.40.206.6 of IEEE® Std 802.11™-2016. The number of bits in the VHT-SIG-B field varies with the channel bandwidth and the assignment depends on whether single user or multiuser scenario in allocated. 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)
80 MHz, 160 MHz
80 MHz, 160 MHz
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.
A four-bit field that is included for multiuser scenarios only.
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 located between the VHT-STF and VHT-SIG-B portion of 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 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 220.127.116.11.5 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.
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.
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.
 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.
 Perahia, E., and R. Stacey. Next Generation Wireless LANs: 802.11n and 802.11ac . 2nd Edition, United Kingdom: Cambridge University Press, 2013.
 IEEE Std 802.11ac™-2013 Adapted and reprinted with permission from IEEE. Copyright IEEE 2013. All rights reserved.