wlanVHTSTF

Generate VHT-STF waveform

Syntax

y = wlanVHTSTF(cfg)

y = wlanVHTSTF(cfg,OversamplingFactor=osf)

Description

y = wlanVHTSTF(cfg) generates a VHT-STF¹ time-domain waveform for the specified transmission parameters. See VHT-STF Processing for waveform generation details.

y = wlanVHTSTF(cfg,OversamplingFactor=osf) generates an oversampled VHT-STF waveform with the specified oversampling factor. For more information about oversampling, see FFT-Based Oversampling.

Examples

Generate VHT-STF Waveform

Create a VHT configuration object with an 80 MHz channel bandwidth. Generate and plot the VHT-STF waveform.

cfgVHT = wlanVHTConfig;
cfgVHT.ChannelBandwidth = 'CBW80';

vstfOut = wlanVHTSTF(cfgVHT);
size(vstfOut);
plot(abs(vstfOut))
xlabel('Samples')
ylabel('Amplitude')

The 80 MHz waveform is a single OFDM symbol with 320 complex time-domain output samples. The waveform contains the repeating short training field pattern.

Input Arguments

cfg — Format configuration

wlanVHTConfig object

Format configuration, specified as a wlanVHTConfig object.

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 — VHT-STF time-domain waveform

matrix

VHT-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.

ChannelBandwidth	NS
'CBW20'	80
'CBW40'	160
'CBW80'	320
'CBW160'	640

See VHT-STF Processing for waveform generation details.

Data Types: double
Complex Number Support: Yes

More About

VHT-STF

The very high throughput short training field (VHT-STF) is a single OFDM symbol (4 μs in length) that is used to improve automatic gain control estimation in a MIMO transmission. It is located between the VHT-SIG-A and VHT-LTF portions of a VHT packet.

The frequency domain sequence used to construct the VHT-STF for a 20 MHz transmission is identical to the L-STF sequence. Duplicate L-STF sequences are frequency shifted and phase rotated to support VHT transmissions for the 40 MHz, 80 MHz, and 160 MHz channel bandwidths. As such, the L-STF and HT-STF are subsets of the VHT-STF.

For a detailed description of the VHT-STF, see Section 21.3.8.3.4 of IEEE^® Std 802.11™-2016.

Algorithms

VHT-STF Processing

The VHT-STF is one OFDM symbol long and is processed for improved gain control in MIMO configurations. For algorithm details, refer to IEEE Std 802.11ac™-2013 [1], Section 22.3.4.6.

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