Generate L-STF waveform
Generate the L-STF waveform for a 40 MHz single antenna VHT packet.
Create a VHT configuration object. Use this object to generate the L-STF waveform.
cfgVHT = wlanVHTConfig('ChannelBandwidth','CBW40'); y = wlanLSTF(cfgVHT); size(y)
ans = 1×2 320 1
plot(abs(y)) xlabel('Samples') ylabel('Amplitude')
The output L-STF waveform contains 320 samples for a 40 MHz channel bandwidth.
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 resultant inverse fast Fourier transform (IFFT) length must be even.
y— L-STF time-domain waveform
(L-STF) 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.
NS is proportional to the channel bandwidth. The time-domain waveform consists of two symbols.
Complex Number Support: Yes
The legacy short training field (L-STF) is the first field of the 802.11™ OFDM PLCP legacy preamble. The L-STF is a component of VHT, HT, and non-HT PPDUs.
The L-STF duration varies with channel bandwidth.
|Channel Bandwidth (MHz)||Subcarrier Frequency Spacing, ΔF (kHz)||Fast Fourier Transform (FFT) Period (TFFT = 1 / ΔF)||L-STF Duration (TSHORT = 10 × TFFT / 4)|
|20, 40, 80, 160, and 320||312.5||3.2 μs||8 μs|
|10||156.25||6.4 μs||16 μs|
|5||78.125||12.8 μs||32 μs|
Because the sequence has good correlation properties, it is used for start-of-packet detection, for coarse frequency correction, and for setting the AGC. The sequence uses 12 of the 52 subcarriers that are available per 20 MHz channel bandwidth segment. For 5 MHz, 10 MHz, and 20 MHz bandwidths, the number of channel bandwidths segments is 1.
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 802.11ac™-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.
 IEEE® Std 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.