wlanHTData

Generate HT-Data field waveform

Syntax

y = wlanHTData(psdu,cfg)

y = wlanHTData(psdu,cfg,scramInit)

y = wlanHTData(___,OversamplingFactor=osf)

Description

y = wlanHTData(psdu,cfg) generates an HT-Data field¹ time-domain waveform for PLCP service data unit psdu and specified transmission parameters cfg. See HT-Data Field Processing for waveform generation details.

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

y = wlanHTData(___,OversamplingFactor=osf) generates an HT-Data field waveform with an oversampling factor. For more information about oversampling, see FFT-Based Oversampling.

Examples

Generate HT-Data Waveform

Generate the waveform signal for a 40 MHz HT-mixed data field with multiple transmit antennas. Create an HT format configuration object. Specify 40 MHz channel bandwidth, two transmit antennas, and two space-time streams.

cfgHT = wlanHTConfig('ChannelBandwidth','CBW40','NumTransmitAntennas',2,'NumSpaceTimeStreams', 2,'MCS',12)

cfgHT = 
  wlanHTConfig with properties:

       ChannelBandwidth: 'CBW40'
    NumTransmitAntennas: 2
    NumSpaceTimeStreams: 2
         SpatialMapping: 'Direct'
                    MCS: 12
          GuardInterval: 'Long'
          ChannelCoding: 'BCC'
             PSDULength: 1024
         AggregatedMPDU: 0
     RecommendSmoothing: 1

Assign PSDULength bytes of random data to a bit stream and generate the HT data waveform.

PSDU =  randi([0 1],cfgHT.PSDULength*8,1);
y = wlanHTData(PSDU,cfgHT);

Determine the size of the waveform.

size(y)

ans = 1×2

        2080           2

The function returns a complex two-column time-domain waveform. Each column contains 2080 samples, corresponding to the HT-Data field for each transmit antenna.

Input Arguments

psdu — PLCP Service Data Unit

vector

PLCP Service Data Unit (PSDU), specified as an N_b-by-1 vector. N_b is the number of bits and equals PSDULength × 8.

Data Types: double

cfg — Transmission parameters

wlanHTConfig object

Transmission parameters, specified as a wlanHTConfig object.

scramInit — Scrambler initialization state

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

Scrambler initialization state for each packet generated, specified as an integer in the interval [1, 127] or as the corresponding binary vector of length seven. The default value of 93 is the example state given in IEEE Std 802.11™-2012, Section L.1.5.2.

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 — HT-Data field time-domain waveform

matrix

HT-Data field time-domain waveform for HT-mixed format, 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.

More About

HT-Data field

The HT-Data field follows the last HT-long training field (HT-LTF) of an HT-mixed packet.

The HT-Data field carries one or more frames from the medium access control (MAC) layer and consists of four subfields.

• Service — Contains 16 zeros to initialize the data scrambler

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

• Tail — Contains six zeros for each encoding stream, required to terminate a convolutional code

• Pad Bits — Variable-length field required to ensure that the HT-Data field consists of an integer number of symbols

PSDU

Physical layer (PHY) service data unit (PSDU). This field is composed of a variable number of octets. The minimum is 0 (zero) and the maximum is 2500. For more information, see IEEE Std 802.11™-2012, Section 15.3.5.7.

Algorithms

HT-Data Field Processing

The HT-Data field follows the last HT-LTF in the packet structure.

The HT-Data field includes the user payload in the PSDU, plus 16 service bits, 6 × N_ES tail bits, and additional padding bits as required to fill out the last OFDM symbol.

For algorithm details, refer to IEEE Std 802.11™-2012 [1], Section 20.3.11. The wlanHTData function performs transmitter processing on the HT-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. STBC and spatial mapping are optional modes for HT format.

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 802.11™-2012 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.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2015b