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wlanVHTSIGB

Generate VHT-SIG-B waveform

Syntax

y= wlanVHTSIGB(cfg)
[y,bits] = wlanVHTSIGB(cfg)

Description

example

y= wlanVHTSIGB(cfg) generates a VHT-SIG-B[1] time-domain waveform for the specified configuration object. See VHT-SIG-B Processing for waveform generation details.

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

Examples

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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 =

   320     1

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

Input Arguments

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Format configuration, specified as a wlanVHTConfig object. The wlanVHTSIGB function uses the object properties indicated.

Channel bandwidth, specified as 'CBW20', 'CBW40', 'CBW80', or 'CBW160'. If the transmission has multiple users, the same channel bandwidth is applied to all users. The default value of 'CBW80' sets the channel bandwidth to 80 MHz.

Data Types: char | string

Number of users, specified as 1, 2, 3, or 4. (NUsers)

Data Types: double

Number of transmit antennas, specified as a scalar integer from 1 to 8.

Data Types: double

Number of space-time streams in the transmission, specified as a scalar or vector.

  • For a single user, the number of space-time streams is a scalar integer from 1 to 8.

  • For multiple users, the number of space-time streams is a 1-by-NUsers vector of integers from 1 to 4, where the vector length, NUsers, 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.

Data Types: double

Spatial mapping scheme, specified as 'Direct', 'Hadamard', 'Fourier', or 'Custom'. The default value of 'Direct' applies when NumTransmitAntennas and NumSpaceTimeStreams are equal.

Data Types: char | string

Spatial mapping matrix, specified as a scalar, matrix, or 3-D array. Use this property to apply a beamforming steering matrix, and to rotate and scale the constellation mapper output vector. If applicable, scale the space-time block coder output instead. SpatialMappingMatrix applies when the SpatialMapping property is set to 'Custom'. For more information, see IEEE Std 802.11™-2012, Section 20.3.11.11.2.

  • When specified as a scalar, a constant value applies to all the subcarriers.

  • When specified as a matrix, the size must be NSTS_Total-by-NT. The spatial mapping matrix applies to all the subcarriers. NSTS_Total is the sum of space-time streams for all users, and NT is the number of transmit antennas.

  • When specified as a 3-D array, the size must be NST-by-NSTS_Total-by-NT. NST is the sum of the occupied data (NSD) and pilot (NSP) subcarriers, as determined by ChannelBandwidth. NSTS_Total is the sum of space-time streams for all users. NT is the number of transmit antennas.

    NST increases with channel bandwidth.

    ChannelBandwidthNumber of Occupied Subcarriers (NST)Number of Data Subcarriers (NSD)Number of Pilot Subcarriers (NSP)
    'CBW20'56524
    'CBW40'1141086
    'CBW80'2422348
    'CBW160'48446816

The calling function normalizes the spatial mapping matrix for each subcarrier.

Example: [0.5 0.3 0.4; 0.4 0.5 0.8] represents a spatial mapping matrix having two space-time streams and three transmit antennas.

Data Types: double
Complex Number Support: Yes

Modulation and coding scheme used in transmitting the current packet, specified as a scalar or vector.

  • For a single user, the MCS value is a scalar integer from 0 to 9.

  • For multiple users, MCS is a 1-by-NUsers vector of integers or a scalar with values from 0 to 9, where the vector length, NUsers, is an integer from 1 to 4.

MCSModulationCoding Rate
0BPSK1/2
1QPSK1/2
2QPSK3/4
316QAM1/2
416QAM3/4
564QAM2/3
664QAM3/4
764QAM5/6
8256QAM3/4
9256QAM5/6

Data Types: double

Number of bytes in the A-MPDU pre-EOF padding, specified as a scalar integer or vector of integers.

  • For a single user, APEPLength is a scalar integer from 0 to 1,048,575.

  • For multi-user, APEPLength is a 1-by-NUsers vector of integers or a scalar with values from 0 to 1,048,575, where the vector length, NUsers, is an integer from 1 to 4.

  • APEPLength = 0 for a null data packet (NDP).

APEPLength is used internally to determine the number of OFDM symbols in the data field. For more information, see IEEE Std 802.11ac™-2013, Table 22-1.

Data Types: double

Output Arguments

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VHT-SIG-B 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.

ChannelBandwidthNS
'CBW20'80
'CBW40'160
'CBW80'320
'CBW160'640

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

Data Types: double
Complex Number Support: Yes

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

The number of output bits changes with the channel bandwidth.

ChannelBandwidthNb
'CBW20'26
'CBW40'27
'CBW80'29
'CBW160'29

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

Data Types: int8

More About

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VHT-SIG-B

The very high throughput signal B field (VHT-SIG-B) is used for multi-user 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. The VHT-SIG-B is defined in IEEE® Std 802.11ac-2013, Section 22.3.8.3.6, and Table 22–14. The number of bits in the VHT-SIG-B field varies with the channel bandwidth and the assignment depends on whether single user or multi-user 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.

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)

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.

VHT-MCS

B16-19 (4)

B17-20 (4)

B19-22 (4)

N/A

N/A

N/A

A four-bit field that 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)

Six zero-bits used to terminate the convolutional code.

Total # bits

26

27

29

26

27

29

 

Bit field repetition

1

2

4

For 160 MHz, the 80 MHz channel is repeated twice.

1

2

4

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 IEEE Std 802.11ac-2013, Table 22-15.

Algorithms

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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.

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

Introduced in R2015b


[1] IEEE Std 802.11ac-2013 Adapted and reprinted with permission from IEEE. Copyright IEEE 2013. All rights reserved.

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