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wlanVHTSTF

Generate VHT-STF waveform

Syntax

y = wlanVHTSTF(cfg)

Description

example

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

Examples

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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')

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. The wlanVHTSTF 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

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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 the 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.

The VHT-STF is defined in IEEE® Std 802.11ac™-2013, Section 22.3.8.3.4.

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.

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.

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