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Wlansymboltimingestimate

Fine symbol timing estimate using L-LTF

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句法

StartOffset = Wlansymboltimingestimate（RXSIG，CBW）
startOffset = wlansymboltimingestimate（rxsig，cbw，阈值）
[[StartOffset，，，，m] = wlansymboltimingestimate（___）

Description

例子

StartOffset=Wlansymboltimingestimate(rxSig，，，，cbw）估计接收波形的开始之间的时间偏移rxSig到开始l-STF1用于频道带宽cbw。

例子

StartOffset=Wlansymboltimingestimate(rxSig，，，，cbw，，，，threshold）specifies the threshold that the decision metric must meet or exceed to obtain a symbol timing estimate.

例子

[[StartOffset，，，，m] = wlansymboltimingestimate（___）还使用先前语法中的任何输入参数组合返回符号正时算法的决策度量。

Examples

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Open Live Script

Detect a received 802.11n™ packet and estimate its symbol timing at 20 dB SNR.

Create an HT format configuration object and TGn channel configuration object.

cfgHT = wlanHTConfig; tgn = wlanTGnChannel;

生成传输波形并在波形开始时添加延迟。

txwaveform = wlanwaveformgenerator（[1; 0; 0; 0; 1]，cfght）;txWaveform = [zeros(100,1);txWaveform];

Pass the waveform through the TGn channel model and add noise.

snr=20;% In decibelsfadedsig = tgn（txwaveform）;rxwaveform = awgn（fadedsig，snr，0）;

Detect the packet. Extract the non-HT fields. Estimate the fine packet offset using the coarse detection for the first symbol of the waveform and the non-HT preamble field indices.

startOffset = wlanpacketDetect（rxwaveform，cfght.channelbandwidth）;ind = wlanfieldIndices（cfght）;nonhtfields = rxwaveform（startOffset+（ind.lstf（1）：ind.lsig（2）），:);startOffset = wlansymboltimingestimate（nonhtfields，...cfgHT.ChannelBandwidth)
StartOffset = 6
Open Live Script

通过将其传递到配置的TGN通道来模拟大量延迟扩展，从而损害了HT波形。检测波形并估计符号正时。调整决策度量阈值，并再次估算符号正时。

Create an HT format configuration object and TGn channel configuration object. Specify the Model-E delay profile, which introduces a large delay spread.

cfgHT = wlanHTConfig; tgn = wlanTGnChannel; tgn.DelayProfile ='Model-E';

生成传输波形并在波形开始时添加延迟。

txwaveform = wlanwaveformgenerator（[1; 0; 0; 0; 1]，cfght）;txWaveform = [zeros(100,1);txWaveform];

Pass the waveform through the TGn channel model and add noise.

SNR = 50;% In decibelsfadedsig = tgn（txwaveform）;rxwaveform = awgn（fadedsig，snr，0）;

Detect the packet. Extract the non-HT fields. Estimate the fine packet offset using the coarse detection for the first symbol of the waveform and the non-HT preamble field indices. Adjust the decision metric threshold and estimate the fine packet offset again.

startOffset = wlanpacketDetect（rxwaveform，cfght.channelbandwidth）;ind = wlanfieldIndices（cfght）;nonhtfields = rxwaveform（startOffset+（ind.lstf（1）：ind.lsig（2）），:);startOffset = wlansymboltimingestimate（nonhtfields，...cfgHT.ChannelBandwidth)
StartOffset = 5
threshold = 0.1
threshold = 0.1000
startOffset = wlansymboltimingestimate（nonhtfields，...CFGHT.CHANNELBANDWIDTH，阈值）
StartOffset = 9

Detecting the correct timing offset is more challenging for a channel model with large delay spread. For large delay spread channels, you can try lowering the threshold setting to see if performance improves in an end-to-end simulation.

Open Live Script

Detect a received 802.11n™ packet and estimate its symbol timing at 15 dB SNR.

创建一个配置对象HT格式。指定两个传输天线和两个时空流。

cfgHT = wlanHTConfig; nAnt = 2; cfgHT.NumTransmitAntennas = nAnt; cfgHT.NumSpaceTimeStreams = nAnt;

显示BPSK调制的MC选择背后的逻辑。

ifcfght.numspacetimestreams == 1 cfght.mcs = 0;ElseifcfgHT.NumSpaceTimeStreams == 2 cfgHT.MCS = 8;ElseifcfgHT.NumSpaceTimeStreams == 3 cfgHT.MCS = 16;ElseifcfgHT.NumSpaceTimeStreams == 4 cfgHT.MCS = 24;end

生成传输波形并在波形开始时添加延迟。

txwaveform = wlanwaveformgenerator（[1; 0; 0; 0; 1]，cfght）;txwaveform = [zeros（100，cfght.numtransmitantennas）; txwaveform];

创建一个TGn通道配置对象transmit antennas and two receive antennas. Specify the Model-B delay profile. Pass the waveform through the TGn channel model and add noise.

tgn = wlanTGnChannel; tgn.NumTransmitAntennas = nAnt; tgn.NumReceiveAntennas = nAnt; tgn.DelayProfile ='Model-B';snr=15;% In decibelsfadedsig = tgn（txwaveform）;rxwaveform = awgn（fadedsig，snr，0）;

Detect the packet. Extract the non-HT fields. Estimate the fine packet offset using the coarse detection for the first symbol of the waveform and the non-HT preamble field indices.

startOffset = wlanpacketDetect（rxwaveform，cfght.channelbandwidth）;ind = wlanfieldIndices（cfght）;nonhtfields = rxwaveform（startOffset+（ind.lstf（1）：ind.lsig（2）），:);startOffset = wlansymboltimingestimate（nonhtfields，...cfgHT.ChannelBandwidth)
StartOffset = 8
Open Live Script

返回802.11ac™数据包的符号正时和决策指标，而无需通道障碍。

创建VHT格式配置对象。指定两个传输天线和两个时空流。

cfgvht = wlanvhtconfig;cfgvht.numtransmitantennas = 2;cfgvht.numspacetimestreams = 2;

生成VHT格式传输波形。在波形开始时添加50样本延迟。

txWaveform = wlanWaveformGenerator([1;0;0;1],cfgVHT); txWaveform = [zeros(50,cfgVHT.NumTransmitAntennas); txWaveform];

Extract the non-HT preamble fields. Obtain the timing offset estimate and decision metric.

ind = wlanfieldindices（cfgvht）;nonhtfields = txwaveform（ind.lstf（1）：ind.lsig（2），:);[startOffset，m] = wlansymboltimingestimate（nonhtfields，...cfgVHT.ChannelBandwidth);

Plot the returned decision metric for the non-HT preamble of the VHT format transmission waveform.

图图（M）Xlabel（“符号正时索引”）ylabel('Decision Metric (M)'）

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

Input Arguments

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received signal containing an L-LTF, specified as a complex-valued matrix of sizens-by-nr。ns是L-LTF中的时间域样本的数量，并且nr是接收天线的数量。

Data Types:单身的|double
Complex Number Support:是的

通道带宽，指定为这些值之一。

  • 'CBW5'- 5 MHz的频道带宽

  • 'cbw10'- 10 MHz的频道带宽

  • 'cbw20'- 20 MHz的频道带宽

  • 'cbw40'-信道带宽of 40 MHz

  • 'CBW80'- 80 MHz的频道带宽

  • 'CBW160'-信道带宽of 160 MHz

  • 'CBW320'-信道带宽of 320 MHz

Data Types:char|细绳

决策阈值，，，，specified as a scalar in the interval [0, 1].

为了最大程度地提高数据包接收性能，您可以尝试此输入的不同价值。对于相对于循环前缀长度的延迟延伸较小的通道，数学®recommends the default value. For a wireless channel with large delay spread with respect to the cyclic prefix length, such as TGn channel with'Model E'delay profile, MathWorks suggests a value of 0.5.

By lowering the threshold setting, you add a nonnegative corrector to the symbol timing estimate as compared to the estimate using the default threshold setting. The range of the timing corrector is [0, CSD ns/sampling duration]. For more information, seeCyclic Shift Delay (CSD)。

Data Types:double

输出参数

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timing offset, in samples, between the start ofrxSigL-STF的开始，在间隔中以整数返回[ -l，，，，ns-2l].lis the length of the L-LTF andnsis the number of samples. Using thecbw输入要确定符号正时的范围，该函数通过与本地生成的接收信号交叉相关的信号来估计L-STF开始的偏移l-LTF第一个天线。

  • 该功能将此输出返回[[]whenns小于l。

  • 该功能将此输出返回a negative integer when the input waveform does not contain a completel-STF。

Data Types:double

Cross-correlation between the received signal and the locally generated L-LTF of the first transmit antenna, returned as a real-valued row vector of lengthns-l+ 1。

Data Types:double

更多关于

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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.

l-STF location within legacy preamble.

the L-STF duration varies with channel bandwidth.

频道带宽（MHz） subcarrier Frequency Spacing,ΔF(kHz) Fast Fourier Transform (FFT) Period (tFFt=1/ΔF） l-STF Duration (tsHORT=10×tFFt/ 4）
20, 40, 80, 160, and 320 312.5 3.2μs 8 μs
10 156.25 6.4μs 16 μs
5 78.125 12.8μs 32 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.

l-LTF

传统长期训练领域（L-LTF）是802.11 OFDM PLCP传统序言中的第二个领域。L-LTF是VHT，HT和NON-HT PPDU的组件。

通道估计，良好的频率偏移估计和细符号正时偏移估计取决于L-LTF。

the L-LTF is composed of a cyclic prefix (CP) followed by two identical long training symbols (C1 and C2). The CP consists of the second half of the long training symbol.

L-LTF持续时间随通道带宽而变化。

频道带宽（MHz） subcarrier Frequency Spacing,ΔF(kHz) Fast Fourier Transform (FFT) Period (tFFt=1/ΔF） 循环前缀或训练符号护罩间隔（GI2）持续时间（tGI2=tFFt/ 2) l-LTF Duration (t长=tGI2+ 2×tFFt）
20, 40, 80, 160, and 320 312.5 3.2μs 1。6 μs 8 μs
10 156.25 6.4μs 3.2μs 16 μs
5 78.125 12.8μs 6.4μs 32 μs

Cyclic Shift Delay (CSD)

A CSD is added to the L-LTF for each transmit antenna, which causes multiple strong peaks in the correlation functionm。the multiple peaks affect the accuracy of fine symbol timing estimation. For more information, see section 21.3.8.2.1 and Table 21-10 of[[1]。

references

[1] IEEE STD 802.11-2020（IEEE STD 802.11-2016的修订版）。“第11部分：无线LAN中型访问控制（MAC）和物理层（PHY）规格。”IEEE信息技术标准 - 系统之间的电信和信息交换。本地和都会区网络 - 特定要求。

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