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wlanLLTF

Generate L-LTF waveform

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Syntax

y = wlanlltf（CFG）
y = wlanLLTF(cfg,OversamplingFactor=osf)

Description

example

y= wlanLLTF(cfg)生成一个L-LTF1time-domain waveform with transmission parameterscfg.

y= wlanLLTF(cfg，过采样factor =osf)生成一个超采样L-LTF waveform with the specified oversampling factor. For more information about oversampling, seeFFT-Based Oversampling.

Examples

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打开实时脚本

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

cfgvht = wlanvhtconfig（'ChannelBandwidth',“CBW40”）；y = wlanlltf（cfgvht）;尺寸（y）
ans =1×2320 1
plot(abs(y)) xlabel('Samples'）ylabel（'振幅')

Figure contains an axes object. The axes object contains an object of type line.

输出L-LTF波形包含40 MHz通道带宽的320个时域样品。

Input Arguments

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Transmission parameters, specified as awlanVHTConfig,wlanhtconfig, orwlanNonHTConfig目的。

过采样因子，指定为标量大于或等于1的标量。过采样的循环前缀长度必须是整数样品数量。

Data Types:single|double|int8|INT16|INT32|int64|uint8|UINT16|uint32|uint64

Output Arguments

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L-LTFtime-domain waveform, returned as anNS-经过-NTmatrix.NSis the number of time-domain samples, andNTis the number of transmit antennas.

NSis proportional to the channel bandwidth. The time-domain waveform consists of two symbols.

ChannelBandwidth NS
'CBW5','CBW10','CBW20' 160
“CBW40” 320
'CBW80' 640
'cbw160' 1280
'CBW320' 2560

Data Types:double
Complex Number Support:Yes

More About

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L-LTF

The legacy long training field (L-LTF) is the second field in the 802.11™ OFDM PLCP legacy preamble. The L-LTF is a component of VHT, HT, and non-HT PPDUs.

Channel estimation, fine frequency offset estimation, and fine symbol timing offset estimation rely on the L-LTF.

L-LTF由循环前缀（CP）组成，然后是两个相同的长训练符号（C1和C2）。CP由长训练符号的后半部分组成。

The L-LTF duration varies with channel bandwidth.

Channel Bandwidth (MHz) Subcarrier Frequency Spacing,δF（千赫） Fast Fourier Transform (FFT) Period (TFFT= 1 /δF) Cyclic Prefix or Training Symbol Guard Interval (GI2) Duration (TGI2=TFFT/ 2） L-LTF Duration (TLONG=TGI2+ 2 ×TFFT)
20、40、80、160和320 312.5 3.2 μs 1.6μs 8 μs
10 156.25 6.4 μs 3.2 μs 16 μs
5 78.125 12.8 μs 6.4 μs 32μs

算法

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L-LTF Processing

TheL-LTF是两个OFDM符号，并遵循VHT，HT和非HT格式的数据包结构中的序言的L-STF。有关算法详细信息，请参阅IEEE STD 802.11ac™-2013[1], Section 22.3.8.2.3 and IEEE Std 802.11-2012[2], Section 20.3.9.3.4.

FFT-Based Oversampling

An超采样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 guardband width relative to the total signal bandwidth, thereby increasing 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 withNFFT子载体组成Ngguardband subcarriers on either side ofNstoccupied bandwidth subcarriers.

基于FFT的过采样。

参考

[1] IEEE STD 802.11AC™-2013 IEEE信息技术标准 - 系统之间的电信和信息交换 - 本地和大都市区域网络 - 特定要求 - 第11部分：无线LAN媒体访问控制（MAC）和物理层（PHY）规格- 修正案4：在6 GHz以下的频段中进行非常高吞吐量的增强功能。

[2]IEEE Std 802.11™-2012 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.

Extended Capabilities

C/C++ Code Generation
使用MATLAB®CODER™生成C和C ++代码。

更小ion History

在R2015B中引入

See Also

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1IEEE®Std 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.