wlanVHTSIGA

Generate VHT-SIG-A waveform

Syntax

y = wlanVHTSIGA(cfg)

[y,bits] = wlanVHTSIGA(cfg)

[___] = wlanVHTSIGA(cfg,OversamplingFactor=osf)

Description

y = wlanVHTSIGA(cfg) generates a VHT-SIG-A¹ time-domain waveform for the specified transmission parameters. See VHT-SIG-A Processing for waveform generation details.

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

[___] = wlanVHTSIGA(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-A Waveform

Create a VHT configuration object, specifying an 80 MHz channel bandwidth.

cfgVHT = wlanVHTConfig(ChannelBandwidth="CBW80");
cfgVHT.ChannelBandwidth = 'CBW80';

Generate a waveform for the VHT-SIG-A field.

y = wlanVHTSIGA(cfgVHT);
size(y)

ans = 1×2

   640     1

The 80 MHz waveform has two OFDM symbols and is a total of 640 samples long. Each symbol contains 320 samples.

Extract VHT-SIG-A Bandwidth Information

Create a VHT configuration object, specifying a 40 MHz channel bandwidth.

cfgVHT = wlanVHTConfig(ChannelBandwidth="CBW40");

Generate the VHT-SIG-A waveform and information bits.

[y,bits] = wlanVHTSIGA(cfgVHT);

Extract the bandwidth from the returned bits and analyze. The bandwidth information is contained in the first two bits.

bwBits = bits(1:2);
bit2int(bwBits,2,false)

ans = int8

1

As defined in IEEE Std 802.11ac-2013, Table 22-12, a value of '1' corresponds to a 40 MHz channel bandwidth.

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-A time-domain waveform

matrix

VHT-SIG-A 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. The time-domain waveform consists of two symbols.

ChannelBandwidth	NS
'CBW20'	160
'CBW40'	320
'CBW80'	640
'CBW160'	1280

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

Data Types: double
Complex Number Support: Yes

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

48-bit column vector

Signaling bits used for the VHT-SIG-A, returned as a 48-bit column vector.

Data Types: int8

More About

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.

Algorithms

VHT-SIG-A Processing

The VHT-SIG-A field includes information required to process VHT format packets.

For algorithm details, refer to IEEE Std 802.11ac™-2013 [1], Section 22.3.4.5. The wlanVHTSIGA function performs transmitter processing on the VHT-SIG-A field and outputs the time-domain waveform.

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