wlanLSTF

Generate L-STF waveform

Syntax

y = wlanLSTF(cfg)

y = wlanLSTF(cfg,OversamplingFactor=osf)

Description

y = wlanLSTF(cfg) generates an L-STF¹ time-domain waveform using the specified transmission parameters.

y = wlanLSTF(cfg,OversamplingFactor=osf) generates an L-STF waveform for the specified oversampling factor. For more information about oversampling, see FFT-Based Oversampling.

Examples

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.

Input Arguments

cfg — Transmission parameters

wlanVHTConfig object | wlanHTConfig object | wlanNonHTConfig object

Transmission parameters, specified as a wlanVHTConfig, wlanHTConfig, or wlanNonHTConfig object.

Example: wlanVHTConfig

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.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

y — L-STF time-domain waveform

matrix

(L-STF) time-domain waveform, 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.

N_S is proportional to the channel bandwidth. The time-domain waveform consists of two symbols.

ChannelBandwidth	NS
'CBW5', 'CBW10', 'CBW20'	160
'CBW40'	320
'CBW80'	640
'CBW160'	1280
'CBW320'	2560

Data Types: double
Complex Number Support: Yes

More About

L-STF

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 EHT, HE, 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, receivers use it for start-of-packet detection, coarse frequency correction, and 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 bandwidth segments is one.

Algorithms

L-STF Processing

The L-STF is two OFDM symbols long and is the first field in the packet structure for the EHT, HE, VHT, HT, and non-HT OFDM formats. For algorithm details, see IEEE Std 802.11ac™-2013 [1], Section 22.3.8.2.2.

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 802.11ac™-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™.

Version History

Introduced in R2015b