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wlanLSTF

Generate L-STF waveform

Syntax

y = wlanLSTF(cfg)

Description

example

y = wlanLSTF(cfg) generates an L-STF[1] time-domain waveform using the specified configuration object.

Examples

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Generate the L-STF waveform for a 40 MHz single antenna VHT packet.

Create a VHT configuration object. Use this object to generate the L-STF waveform.

cfgVHT = wlanVHTConfig('ChannelBandwidth','CBW40');
y = wlanLSTF(cfgVHT);
size(y)
plot(abs(y))
xlabel('Samples')
ylabel('Amplitude')
ans =

   320     1

The output L-STF waveform contains 320 samples for a 40 MHz channel bandwidth.

Input Arguments

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Format configuration, specified as a wlanVHTConfig, wlanHTConfig, or wlanNonHTConfig object. For a specified format, the wlanLSTF function uses only the object properties indicated.

Transmission FormatApplicable Object Properties

VHT

ChannelBandwidth, NumTransmitAntennas

HT

ChannelBandwidth, NumTransmitAntennas

non-HT

See note 1

ChannelBandwidth, NumTransmitAntennas

Note:
  1. For non-HT format, when channel bandwidth is 5 MHz or 10 MHz, NumTransmitAntennas is not applicable because only one transmit antenna is permitted.

Example: wlanVHTConfig

Output Arguments

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(L-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. The time-domain waveform consists of two symbols.

ChannelBandwidthNS
'CBW5', 'CBW10', 'CBW20'160
'CBW40'320
'CBW80'640
'CBW160'1280

Data Types: double
Complex Number Support: Yes

More About

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L-STF

The legacy short training field (L-STF) is the first field of the 802.11™ OFDM PLCP legacy preamble. The L-STF is a component of VHT, HT, and non-HT PPDUs.

The L-STF duration varies with channel bandwidth.

Channel Bandwidth (MHz)Subcarrier Frequency Spacing, ΔF (kHz)Fast Fourier Transform (FFT) Period (TFFT = 1 / ΔF)L-STF Duration (TSHORT = 10 × TFFT / 4)
20, 40, 80, and 160312.53.2 μs8 μs
10156.256.4 μs16 μs
578.12512.8 μs32 μs

Because the sequence has good correlation properties, it is used for start-of-packet detection, for coarse frequency correction, and for setting the AGC. The sequence uses 12 of the 52 subcarriers that are available per 20 MHz channel bandwidth segment. For 5 MHz, 10 MHz, and 20 MHz bandwidths, the number of channel bandwidths segments is 1.

Algorithms

The L-STF is two OFDM symbols long and is the first field in the packet structure for the VHT, HT, and non-HT OFDM formats. For algorithm details, refer to IEEE Std 802.11ac™-2013 [1], Section 22.3.8.2.2.

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 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.

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