Generate HT-Data field 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
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.
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.
psdu— PLCP Service Data Unit
PLCP Service Data Unit (PSDU), specified as an
Nb is the number of bits
PSDULength × 8.
cfg— Transmission parameters
Transmission parameters, specified as a
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.
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
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 126.96.36.199.
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 , Section 20.3.11.
wlanHTData function performs transmitter
processing on the HT-Data field and
outputs the time-domain waveform for NT transmit
|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.
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.
 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.
 IEEE Std 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.