Documentation

This is machine translation

Translated by Microsoft
Mouseover text to see original. Click the button below to return to the English verison of the page.

Note: This page has been translated by MathWorks. Please click here
To view all translated materals including this page, select Japan from the country navigator on the bottom of this page.

wlanVHTLTF

Generate VHT-LTF waveform

Syntax

y = wlanVHTLTF(cfg)

Description

example

y = wlanVHTLTF(cfg) generates a VHT-LTF [1] time-domain waveform for the specified configuration object. See VHT-LTF Processing for waveform generation details.

Examples

collapse all

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 =

   320     1

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

Input Arguments

collapse all

Format configuration, specified as a wlanVHTConfig object. The wlanVHTLTF function uses the object properties indicated.

Channel bandwidth, specified as 'CBW20', 'CBW40', 'CBW80', or 'CBW160'. If the transmission has multiple users, the same channel bandwidth is applied to all users. The default value of 'CBW80' sets the channel bandwidth to 80 MHz.

Data Types: char | string

Number of transmit antennas, specified as a scalar integer from 1 to 8.

Data Types: double

Number of space-time streams in the transmission, specified as a scalar or vector.

  • For a single user, the number of space-time streams is a scalar integer from 1 to 8.

  • For multiple users, the number of space-time streams is a 1-by-NUsers vector of integers from 1 to 4, where the vector length, NUsers, is an integer from 1 to 4.

Example: [1 3 2] is the number of space-time streams for each user.

Note

The sum of the space-time stream vector elements must not exceed eight.

Data Types: double

Spatial mapping scheme, specified as 'Direct', 'Hadamard', 'Fourier', or 'Custom'. The default value of 'Direct' applies when NumTransmitAntennas and NumSpaceTimeStreams are equal.

Data Types: char | string

Spatial mapping matrix, specified as a scalar, matrix, or 3-D array. Use this property to apply a beamforming steering matrix, and to rotate and scale the constellation mapper output vector. If applicable, scale the space-time block coder output instead. SpatialMappingMatrix applies when the SpatialMapping property is set to 'Custom'. For more information, see IEEE Std 802.11™-2012, Section 20.3.11.11.2.

  • When specified as a scalar, a constant value applies to all the subcarriers.

  • When specified as a matrix, the size must be NSTS_Total-by-NT. The spatial mapping matrix applies to all the subcarriers. NSTS_Total is the sum of space-time streams for all users, and NT is the number of transmit antennas.

  • When specified as a 3-D array, the size must be NST-by-NSTS_Total-by-NT. NST is the sum of the occupied data (NSD) and pilot (NSP) subcarriers, as determined by ChannelBandwidth. NSTS_Total is the sum of space-time streams for all users. NT is the number of transmit antennas.

    NST increases with channel bandwidth.

    ChannelBandwidthNumber of Occupied Subcarriers (NST)Number of Data Subcarriers (NSD)Number of Pilot Subcarriers (NSP)
    'CBW20'56524
    'CBW40'1141086
    'CBW80'2422348
    'CBW160'48446816

The calling function normalizes the spatial mapping matrix for each subcarrier.

Example: [0.5 0.3 0.4; 0.4 0.5 0.8] represents a spatial mapping matrix having two space-time streams and three transmit antennas.

Data Types: double
Complex Number Support: Yes

Output Arguments

collapse all

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

collapse all

VHT-LTF

The very high throughput long training field (VHT-LTF) is located between the VHT-STF and VHT-SIG-B portion of 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 MCS. Each symbol is 4 μs long. A maximum of eight symbols are permitted in the VHT-LTF.

The VHT-LTF is defined in IEEE® Std 802.11ac™-2013, Section 22.3.8.3.5.

Algorithms

collapse all

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.

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

Introduced in R2015b


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

Was this topic helpful?