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wlanHTSTF

Generate HT-STF waveform

Description

example

y = wlanHTSTF(cfg) generates an HT-STF[1] time-domain waveform for an HT-mixed transmission parameterized by cfg.

y = wlanHTSTF(cfg,OversamplingFactor=osf) generates an oversampled HT-mixed waveform with the specified oversampling rate. For more information about oversampling, see FFT-Based Oversampling.

Examples

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Create a wlanHTConfig object with a 40 MHz bandwidth.

cfg = wlanHTConfig('ChannelBandwidth','CBW40');

Generate an HT-STF. The function returns a complex output of 160 samples.

stf = wlanHTSTF(cfg);
size(stf)
ans = 1×2

   160     1

Change the channel bandwidth to 20 MHz and create a new HT-STF.

cfg.ChannelBandwidth = 'CBW20';
stf = wlanHTSTF(cfg);

Verify that the number of samples has been halved due to the bandwidth reduction.

size(stf)
ans = 1×2

    80     1

Input Arguments

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Transmission parameters, specified as a wlanHTConfig 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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HT-STF waveform, returned as an NS-by-NT matrix. NS is the number of samples, and NT is the number of transmit antennas.

Data Types: double
Complex Number Support: Yes

More About

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HT-STF

The high throughput short training field (HT-STF) is located between the HT-SIG and HT-LTF fields of an HT-mixed packet. The HT-STF is 4 μs in length and is used to improve automatic gain control estimation for a MIMO system. For a 20 MHz transmission, the frequency sequence used to construct the HT-STF is identical to that of the L-STF. For a 40 MHz transmission, the upper subcarriers of the HT-STF are constructed from a frequency-shifted and phase-rotated version of the L-STF.

HT-mixed

As described in IEEE Std 802.11™-2012, Section 20.1.4, high throughput mixed (HT-mixed) format packets contain a preamble compatible with IEEE Std 802.11-2012, Section 18 and Section 19 receivers. Non-HT (Section 18 and Section19) STAs can decode the non-HT fields (L-STF, L-LTF, and L-SIG). The remaining preamble fields (HT-SIG, HT-STF, and HT-LTF) are for HT transmission, so the Section 18 and Section 19 STAs cannot decode them. The HT portion of the packet is described in IEEE Std 802.11-2012, Section 20.3.9.4. Support for the HT-mixed format is mandatory.

Algorithms

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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 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.

FFT-based oversampling.

References

[1] 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.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Introduced in R2015b

[1] IEEE® Std 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.