wlanVHTSIGB

Generate VHT-SIG-B waveform

Syntax

y= wlanVHTSIGB(cfg)

[y,bits] = wlanVHTSIGB(cfg)

[___ = wlanVHTSIGB(cfg,OversamplingFactor=osf)

Description

y= wlanVHTSIGB(cfg) generates a VHT-SIG-B¹ time-domain waveform for the specified transmission parameters. See VHT-SIG-B Processing for waveform generation details.

[y,bits] = wlanVHTSIGB(cfg) also outputs VHT-SIG-B information bits.

[___ = wlanVHTSIGB(cfg,OversamplingFactor=osf) generates an oversampled waveform with the specified oversampling factor. For more information about oversampling, see FFT-Based Oversampling.

Examples

Generate VHT-SIG-B Waveform

Generate the VHT-SIG-B waveform for an 80 MHz transmission packet.

Create a VHT configuration object, assign an 80 MHz channel bandwidth, and generate the waveform.

cfgVHT = wlanVHTConfig('ChannelBandwidth','CBW80');
vhtsigb = wlanVHTSIGB(cfgVHT);
size(vhtsigb)

ans = 1×2

   320     1

The 80 MHz waveform has one OFDM symbol and is a total of 320 samples long.

Input Arguments

cfg — Transmission parameters

wlanVHTConfig object

Transmission parameters, specified as a wlanVHTConfig object.

osf — Oversampling factor

1 (default) | scalar greater than or equal to 1

Oversampling factor, specified as a scalar greater than or equal to 1. The oversampled cyclic prefix length must be an integer number of samples.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

y — VHT-SIG-B time-domain waveform

matrix

VHT-SIG-B time-domain waveform, returned as an N_S-by-N_T matrix. N_S is the number of time-domain samples and N_T is the number of transmit antennas.

N_S is proportional to the channel bandwidth.

ChannelBandwidth	NS
'CBW20'	80
'CBW40'	160
'CBW80'	320
'CBW160'	640

See VHT-SIG-B Processing. for waveform generation details.

Data Types: double
Complex Number Support: Yes

bits — Signaling bits used for the VHT-SIG-B field

N_bits column vector

Signaling bits used for VHT-SIG-B field, returned as an N_bits column vector. N_bits is the number of bits.

The number of output bits changes with the channel bandwidth.

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

See VHT-SIG-B Processing. for waveform generation details.

Data Types: int8

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.

Algorithms

VHT-SIG-B Processing

The VHT-SIG-B field is used to set up the data rate and to fine-tune MIMO reception. For single user packets, since the length information can be recovered from the L-SIG and VHT-SIG-A field information, it is not strictly required for the receiver to decode the VHT-SIG-B field.

For algorithm details, refer to IEEE Std 802.11ac™-2013 [1], Section 22.3.4.8.

FFT-Based Oversampling

An oversampled signal is a signal sampled at a frequency that is higher than the Nyquist rate. WLAN signals maximize occupied bandwidth by using small guardbands, which can pose problems for anti-imaging and anti-aliasing filters. Oversampling increases the guardband width relative to the total signal bandwidth, which increases the number of samples in the signal.

This function performs oversampling by using a larger IFFT and zero pad when generating an OFDM waveform. This diagram shows the oversampling process for an OFDM waveform with N_FFT subcarriers made up of N_g guardband subcarriers on either side of N_st occupied bandwidth subcarriers.

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.

Extended Capabilities

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

Version History

Introduced in R2015b