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wlanVHTSTF

Generate VHT-STF waveform

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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.

example

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

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Open Live Script

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')

Figure contains an axes object. The axes object with xlabel Samples, ylabel Amplitude contains an object of type line.

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

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Format configuration, specified as a wlanVHTConfig object.

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

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VHT-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.

ChannelBandwidthNS
'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

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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 VHT-STF in 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

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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 NFFT subcarriers made up of Ng guardband subcarriers on either side of Nst occupied bandwidth subcarriers.

FFT-based oversampling

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

See Also

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1 IEEE Std 802.11ac-2013 Adapted and reprinted with permission from IEEE. Copyright IEEE 2013. All rights reserved.