wlanVHTLTF

Generate VHT-LTF waveform

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.

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

Generate VHT-LTF Waveform

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

cfg — Transmission parameters

wlanVHTConfig object

Transmission parameters, 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.

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

Output Arguments

y — VHT-LTF time-domain waveform

matrix

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

Data Types: double
Complex Number Support: Yes

More About

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.

Receivers use this field 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. The VHT-LTF consists of eight symbols at most.

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

Algorithms

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 (N_VHTLTF) is derived from the total number of space-time streams (N_{STS_Total}). N_{STS_Total} = ΣN_STS(u) for user u, u = 0,…, N_Users–1 and N_STS(u) is the number of space-time streams per user.

NSTS_Total	NVHTLTF
1	1
2	2
3	4
4	4
5	6
6	6
7	8
8	8

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 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