wlanVHTData

Generate VHT-Data field

Syntax

y = wlanVHTData(psdu,cfg)

y = wlanVHTData(psdu,cfg,scramInit)

y = wlanVHTData(___,OversamplingFactor=osf)

Description

y = wlanVHTData(psdu,cfg) generates a VHT-Data field¹ time-domain waveform from user data bits psdu for transmission parameters cfg. See VHT-Data Field Processing for waveform generation details.

y = wlanVHTData(psdu,cfg,scramInit) uses scramInit for the scrambler initialization state.

y = wlanVHTData(___,OversamplingFactor=osf) generates an oversampled VHT-Data waveform with the specified oversampling factor. For more information about oversampling, see FFT-Based Oversampling.

Examples

Generate VHT-Data Waveform

Generate the waveform for a MIMO 20 MHz VHT-Data field.

Create a VHT configuration object. Assign a 20 MHz channel bandwidth, two transmit antennas, two space-time streams, and set MCS to four.

cfgVHT = wlanVHTConfig('ChannelBandwidth','CBW20','NumTransmitAntennas',2,'NumSpaceTimeStreams',2,'MCS',4);

Generate the user payload data and the VHT-Data field waveform.

psdu = randi([0 1],cfgVHT.PSDULength*8,1);
y = wlanVHTData(psdu,cfgVHT);
size(y)

ans = 1×2

        2160           2

The 20 MHz waveform is an array with two columns, corresponding to two transmit antennas. There are 2160 complex samples in each column.

y(1:10,:)

ans = 10×2 complex

  -0.0598 + 0.1098i  -0.1904 + 0.1409i
   0.6971 - 0.3068i  -0.0858 - 0.2701i
  -0.1284 + 0.9268i  -0.8318 + 0.3314i
  -0.1180 + 0.0731i   0.1313 + 0.4956i
   0.3591 + 0.5485i   0.9749 + 0.2859i
  -0.9751 + 1.3334i   0.0559 + 0.4248i
   0.0881 - 0.8230i  -0.1878 - 0.2959i
  -0.2952 - 0.4433i  -0.1005 - 0.4035i
  -0.5562 - 0.3940i  -0.1292 - 0.5976i
   1.0999 + 0.3292i  -0.2036 - 0.0200i

Input Arguments

psdu — PHY service data unit

binary column vector | row cell array

PHY service data unit (PSDU), specified as a binary column vector or row cell array.

If you specify psdu as a column vector, it must have N_b elements. N_b is the number of bits and is equal to the PSDULength property of the cfg input multiplied by eight.

If you specify psdu as a row cell array, its length must be equal to the NumUsers property of the cfg input. The ith element of the cell array must be a binary column vector. The length of this vector must be equal to eight times the ith element of the PSDULength property.

Data Types: double | int8

cfg — Transmission parameters

wlanVHTConfig object

Transmission parameters, specified as a wlanVHTConfig object.

scramInit — Scrambler initialization state

93 (default) | integer in the interval [1, 127] | integer row vector | binary vector | binary matrix

Initial scrambler state of the data scrambler for each packet generated, specified as an integer, a binary vector, a 1-by-N_U integer row vector, or a 7-by-N_U binary matrix. N_U is the number of users, from 1 to 4. If specified as an integer or binary vector, the setting applies to all users. If specified as a row vector or binary matrix, the setting for each user is specified in the corresponding column, as an integer in the interval [1, 127] or the corresponding binary vector.

The scrambler initialization used on the transmission data follows the process described in IEEE^® Std 802.11™-2012, Section 18.3.5.5 and IEEE Std 802.11ad™-2012, Section 21.3.9. The header and data fields that follow the scrambler initialization field (including data padding bits) are scrambled by XORing each bit with a length-127 periodic sequence generated by the polynomial S(x) = x⁷+x⁴+1. The octets of the PSDU are placed into a bit stream and, within each octet, bit 0 (LSB) is first and bit 7 (MSB) is last. This figure shows the generation of the sequence and the XOR operation.

Conversion from integer to bits uses left-MSB orientation. For example, initializing the scrambler with decimal 1, the bits map to these elements.

Element	X7	X6	X5	X4	X3	X2	X1
Bit Value	0	0	0	0	0	0	1

To generate the bit stream equivalent to a decimal, use the int2bit function. For example, for decimal 1:

int2bit(1,7)'
ans =

     0     0     0     0     0     0     1

Example: [1;0;1;1;1;0;1] conveys the scrambler initialization state of 93 as a binary vector.

Data Types: double | int8

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-Data field time-domain waveform

matrix

VHT-Data field 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. See VHT-Data Field Processing for waveform generation details.

More About

VHT-Data field

The VHT-Data field carries one or more frames from the medium access control (MAC) layer. This field follows the VHT-SIG-B field in a VHT PPDU.

For a detailed description of the VHT-Data field, see section 21.3.10 of IEEE Std 802.11-2020. The VHT Data field consists of four subfields.

• Service field — Contains a seven-bit scrambler initialization state, one bit reserved for future considerations, and eight bits for the VHT-SIG-B cyclic redundancy check (CRC) field

• PSDU — Variable-length field containing a PLCP service data unit

• PHY Pad — Variable number of bits passed to the transmitter to create a complete OFDM symbol

• Tail — Bits required to terminate a convolutional code (not required when the transmission uses LDPC channel coding)

PSDU

Physical layer (PHY) Service Data Unit (PSDU). A PSDU can consist of one medium access control (MAC) protocol data unit (MPDU) or several MPDUs in an aggregate MPDU (A-MPDU). In a single user scenario, the VHT-Data field contains one PSDU. In a multi-user scenario, the VHT-Data field carries up to four PSDUs for up to four users.

Algorithms

VHT-Data Field Processing

The VHT-Data field encodes the service, PSDU, pad bits, and tail bits. The wlanVHTData function performs transmitter processing on the VHT-Data field and outputs the time-domain waveform for N_T transmit antennas.

NES is the number of BCC encoders.

NSS is the number of spatial streams.

NSTS is the number of space-time streams.

NT is the number of transmit antennas.

BCC channel coding is shown.

For algorithm details, refer to IEEE Std 802.11ac™-2013 [1], Section 22.3.4.9 and 22.3.4.10, respectively, single user and multi-user.

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