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wlanHTData

Generate HT-Data field waveform

Description

example

y = wlanHTData(psdu,cfg) generates the HT-Data field[1] time-domain waveform for the input PLCP service data unit, psdu, and specified configuration object, cfg. See HT-Data Field Processing for waveform generation details.

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

Examples

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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

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

Data Types: double

Format configuration, specified as a wlanHTConfig object.

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 (Physical Layer Service Data Unit) are placed into a bit stream, and within each octet, bit 0 (LSB) is first and bit 7 (MSB) is last. The generation of the sequence and the XOR operation are shown in this figure:

Conversion from integer to bits uses left-MSB orientation. For the initialization of the scrambler with decimal 1, the bits are mapped to the elements shown.

ElementX7X6X5X4X3X2X1
Bit Value0000001

To generate the bit stream equivalent to a decimal, use de2bi. For example, for decimal 1:

de2bi(1,7,'left-msb')
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

Output Arguments

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HT-Data field time-domain waveform for HT-mixed format, returned as an NS-by-NT matrix. NS is the number of time domain samples, and NT is the number of transmit antennas.

More About

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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 is 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

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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 × NES 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 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. STBC and spatial mapping are optional modes for HT format.

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™.

Introduced in R2015b

[1] IEEE Std 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.