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wlanVHTLTF

Generate VHT-LTF waveform

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Syntax

y = wlanVHTLTF(cfg)
y = wlanVHTLTF(cfg,OversamplingFactor=osf)

Description

y = wlanVHTLTF(cfg) generates a VHT-LTF 1 time-domain waveform for the specified transmission parameters. See VHT-LTF Processing for waveform generation details.

example

y = wlanVHTLTF(cfg,OversamplingFactor=osf) generates an oversampled VHT-LTF 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.

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

Generate a VHT-LTF waveform.

vltfOut = wlanVHTLTF(cfgVHT);
size(vltfOut)
ans = 1×2

   320     1

The 80 MHz waveform is a single OFDM symbol with 320 complex output samples.

Input Arguments

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Transmission parameters, 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.

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

Output Arguments

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VHT-LTF time-domain waveform, returned as an (NS × NVHTLTF)-by-NT matrix. NS is the number of time-domain samples per NVHTLTF, where NVHTLTF is the number of OFDM symbols in the VHT-LTF. 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-LTF Processing for waveform generation details.

Data Types: double
Complex Number Support: Yes

More About

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VHT-LTF

The very high throughput long training field (VHT-LTF) is between the VHT-STF and VHT-SIG-B portion of the VHT packet.

The VHT-LTF in the VHT packet

It is used for MIMO channel estimation and pilot subcarrier tracking. The VHT-LTF includes one VHT long training symbol for each spatial stream indicated by the selected modulation and coding scheme (MCS). Each symbol is 4 μs long. A maximum of eight symbols are permitted in the VHT-LTF.

For a detailed description of the VHT-LTF, see Section 21.3.8.3.5 of IEEE® Std 802.11™-2016.

Algorithms

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VHT-LTF Processing

The VHT-LTF is used for MIMO channel estimation and pilot subcarrier tracking. The number of OFDM symbols in the VHT-LTF (NVHTLTF) is derived from the total number of space-time streams (NSTS_Total). NSTS_Total = ΣNSTS(u) for user u, u = 0,…, NUsers–1 and NSTS(u) is the number of space-time streams per user.

NSTS_TotalNVHTLTF
11
22
34
44
56
66
78
88

For algorithm details refer to IEEE Std 802.11ac™-2013 [1], Section 22.3.4.7.

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.