Generate VHT-SIG-A waveform
Generate the VHT-SIG-A waveform for an 80 MHz transmission packet.
Create a VHT configuration object, assign an 80 MHz channel bandwidth, and generate the waveform.
cfgVHT = wlanVHTConfig; cfgVHT.ChannelBandwidth = 'CBW80'; 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.
Generate the VHT-SIG-A waveform for a 40 MHz transmission packet.
Create a VHT configuration object, and assign a 40 MHz channel bandwidth.
cfgVHT = wlanVHTConfig; cfgVHT.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); bi2de(bwBits)
ans = 2x1 int8 column vector 1 0
As defined in IEEE Std 802.11ac-2013, Table 22-12, a value of
'1' corresponds to 40 MHz bandwidth.
cfg— Format configuration
Format configuration, specified as a
wlanVHTSIGA function uses the object properties
Applicable Object Properties
y— VHT-SIG-A time-domain waveform
VHT-SIG-A time-domain waveform, returned as an NS-by-NT matrix. NS is the number of time-domain samples, and NT is the number of transmit antennas.
NS is proportional to the channel bandwidth. The time-domain waveform consists of two symbols.
See VHT-SIG-A Processing for waveform generation details.
Complex Number Support: Yes
bits— Signaling bits used for the VHT-SIG-A field
Signaling bits used for the VHT-SIG-A, returned as a 48-bit column vector.
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.
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 is defined in IEEE Std 802.11ac-2013, Section 18.104.22.168.3.
The VHT-SIG-A field includes these components. The bit field structures for VHT-SIG-A1 and VHT-SIG-A2 vary for single user or multiuser 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.
NSTS — A three-bit field for a single user or 4 three-bit fields for a multiuser 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 if 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 Coding — A bit field that indicates if convolutional or LDPC coding is used for a single user or for user MU in a multiuser 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 multiuser scenario, it indicates 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.
 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.
 IEEE Std 802.11ac-2013 Adapted and reprinted with permission from IEEE. Copyright IEEE 2013. All rights reserved.