wlanVHTSIGBRecover

Recover VHT-SIG-B information bits

Syntax

recBits = wlanVHTSIGBRecover(rxSig,chEst,noiseVarEst,cbw)

recBits = wlanVHTSIGBRecover(rxSig,chEst,noiseVarEst,cbw,userNumber,numSTS)

[recBits,eqSym] = wlanVHTSIGBRecover(___)

[recBits,eqSym,cpe] = wlanVHTSIGBRecover(___)

recBits = wlanVHTSIGBRecover(___,Name=Value)

Description

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

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

recBits = wlanVHTSIGBRecover(___,Name=Value) specifies algorithm parameters by using one or more name-value arguments in addition to any combination of input or output arguments from the previous syntaxes.

Examples

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.

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');
isequal(txBits,rxBits)

ans = logical
   1

Recover VHT-SIG-B Using Zero-Forcing Equalizer

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 2x2 MIMO Channel

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

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

rxSig — Received VHT-SIG-B

matrix

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

Channel Bandwidth	NS
'CBW20'	80
'CBW40'	160
'CBW80'	320
'CBW160'	640

N_R is the number of receive antennas.

Data Types: double | single
Complex Number Support: Yes

chEst — Channel estimate

3-D array

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

N_ST increases with channel bandwidth.

ChannelBandwidth	Number of Occupied Subcarriers (NST)	Number of Data Subcarriers (NSD)	Number of Pilot Subcarriers (NSP)
'CBW20'	56	52	4
'CBW40'	114	108	6
'CBW80'	242	234	8
'CBW160'	484	468	16

The channel estimate is based on the VHT-LTF.

Data Types: double | single

noiseVarEst — Noise variance estimate

nonnegative scalar

Noise variance estimate, specified as a nonnegative scalar.

Data Types: double | single

cbw — Channel bandwidth

'CBW20' | 'CBW40' | 'CBW80' | 'CBW160'

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

Data Types: char | string

userNumber — Number of the user

integer from 1 to N_Users

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

numSTS — Number of space-time streams

1-by-N_Users vector of integers from 1 to 4

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

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

Note

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.

Example: PilotPhaseTracking='None' disables pilot phase tracking.

OFDMSymbolOffset — OFDM symbol sampling offset

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

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.

Data Types: double

EqualizationMethod — Equalization method

'MMSE' (default) | 'ZF'

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

PilotPhaseTracking — Pilot phase tracking

'PreEQ' (default) | 'None'

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

recBits — Recovered VHT-SIG information

vector

Recovered VHT-SIG-B information bits, returned as an N_b-by-1 column vector. N_b 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.

ChannelBandwidth	Nb
'CBW20'	26
'CBW40'	27
'CBW80'	29
'CBW160'	29

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

eqSym — Equalized symbols

matrix

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

N_SD increases with the channel bandwidth.

ChannelBandwidth	NSD
'CBW20'	52
'CBW40'	108
'CBW80'	234
'CBW160'	468

cpe — Common phase error

column vector

Common phase error in radians, returned as a scalar.

More About

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-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.

PPDU

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.

Algorithms

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.

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.

For VHT-SIG-B details, refer to IEEE Std 802.11ac™-2013 [1], Section 22.3.4.8, and Perahia [2], Section 7.3.2.4.

References

[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

R2024a: Single precision support

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