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wlanVHTData

Generate VHT-Data field

Description

example

y = wlanVHTData(psdu,cfg) generates a VHT-Data field[1] 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

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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

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PHY service data unit (PSDU), specified as an Nb-by-1 vector. Nb is the number of bits and equals PSDULength × 8.

Data Types: double

Transmission parameters, specified as a wlanVHTConfig object.

Initial scrambler state of the data scrambler for each packet generated, specified as an integer, a binary vector, a 1-by-NU integer row vector, or a 7-by-NU binary matrix. NU 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.

ElementX7X6X5X4X3X2X1
Bit Value0000001

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

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

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

More About

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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 PPDUs.

For a detailed description of the VHT-Data field, see section 21.3.10 of IEEE Std 802.11-2016. 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

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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 NT 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 guardband width relative to the total signal bandwidth, thereby increasing 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 NFFT subcarriers comprising Ng guardband subcarriers on either side of Nst occupied bandwidth subcarriers.

FFT-based oversampling.

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™.

Introduced in R2015b

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