Comm.CoarseFrequencyCompensator

补偿PAM，PSK或QAM信号的频率偏移

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描述

这Comm.CoarseFrequencyCompensator系统对象™ compensates for the frequency offset of received signals using an open-loop technique.

To compensate for the frequency offset of a PAM, PSK, or QAM signal:

创建Comm.CoarseFrequencyCompensatorobject and set its properties.
Call the object with arguments, as if it were a function.

To learn more about how System objects work, see什么是系统对象？

创建

Syntax

croumfreqcomp = comm.coarsefrequencyCompensator

crialfreqcomp = comm。

描述

example

croumfreqcomp= Comm.CoarseFrequencyCompensatorcreates a coarse frequency offset compensator System object. This object uses an open-loop technique to estimate and compensate for the carrier frequency offset in a received signal. For more information about the estimation algorithm options, seeAlgorithms。

croumfreqcomp= Comm.CoarseFrequencyCompensator(Name,Value)specifies properties using one or more name-value arguments. For example,调制='QPSK'specifies quadrature phase-shift keying modulation.

特性

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除非另有说明，否则属性是不可否认，这意味着您在调用对象后不能更改其值。呼叫时锁定对象，然后releasefunction unlocks them.

如果财产是可调, you can change its value at any time.

For more information on changing property values, seeSystem Design in MATLAB Using System Objects。

`调制`—调制type
`'QAM'`（默认）|`'8psk'`|`'bpsk'`|`'OQPSK'`|`'PAM'`|`'QPSK'`

调制类型,指定为一个,

'bpsk'– Binary phase shift keying
'QPSK'– Quadrature phase shift keying
'OQPSK'– Offset quadrature phase shift keying
'8psk'– 8-phase shift keying
'PAM'- 脉冲振幅调制
'QAM'- 正交振幅调制

数据类型：char|细绳

`Algorithm`—Algorithm used to estimate frequency offset
`'FFT-based'`（默认）|`“基于相关”'`

Algorithm used to estimate the frequency offset, specified as'FFT-based'or“基于相关”'。

Dependency

要启用此属性，请设置调制to'bpsk','QPSK','8psk', or'PAM'。该表显示了调制类型和估计算法的有效组合。

调制	FFT-Based艾尔gorithm	Correlation-Based Algorithm
`bpsk`,`QPSK`,`8psk`,`PAM`	是的	是的
`OQPSK`,`QAM`	是的	No

Use the correlation-based algorithm for HDL implementations and for other situations in which you want to avoid using an FFT.

数据类型：char|细绳

`FrequencyResolution`—Frequency resolution
`0.001`（默认）|positive scalar

Frequency resolution for the offset frequency estimation in hertz, specified as a positive scalar. This property establishes the FFT length used to perform spectral analysis and must be less than the sample rate.

数据类型：双倍的

`最大频率OFFENDSET`—Maximum measurable frequency offset
`0.05`（默认）|positive scalar

Maximum measurable frequency offset in hertz, specified as a positive scalar.

该物业的价值必须小于f_samp/M。For more details, see基于相关的估计。

Dependency

要启用此属性，请设置Algorithmproperty to“基于相关”'。

数据类型：双倍的

`采样率`—Sample rate
`1`（默认）|positive scalar

Sample rate in samples per second, specified as a positive scalar.

数据类型：双倍的

`Samplespersymbol`—Samples per symbol
`4`（默认）|即使是整数,大于或等于`4`

Samples per symbol, specified as an even positive integer greater than or equal to4。

Dependency

要启用此属性，请设置调制to'OQPSK'。

Usage

Syntax

y = coarseFreqComp(x)

[y,estimate] = coarseFreqComp(x)

描述

example

y= coolfreqcomp（x)returns a signal that compensates for the carrier frequency offset of the input signal.

example

[y,estimate] = coolfreqcomp（x)returns a scalar estimate of the frequency offset.

Input Arguments

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`x`—输入信号
column vector

输入信号，指定为列向量。

数据类型：single|双倍的

输出参数

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`y`— Compensated output signal
complex column vector

补偿输出信号，作为复杂的列向量返回，具有相同的维度和数据类型与输入x。

`estimate`- 频率偏移的估计值
scalar

频率偏移的估计，返回为标量。

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object namedobj，使用此语法：

release(obj)

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特定于`Comm.CoarseFrequencyCompensator`

`info`	有关粗频率补偿器的特征信息
`clone`	创建重复系统对象
`isLocked`	确定是否系统对象正在使用

Common to All System Objects

`步`	Run系统对象algorithm
`release`	Release resources and allow changes to系统对象property values and input characteristics
`重置`	重置内部状态系统对象

例子

collapse all

Compensate for Frequency Offset in QPSK Signal

Open Live Script

补偿在嘈杂的QPSK信号上施加的4 kHz频率偏移。

Set up the example parameters.

nsym = 2048;％输入符号数量sps = 4;% Samples per symbolnSamp = nSym*sps;样品数量的％fs = 80000;% Sampling frequency (Hz)

创建一个平方根凸起的余弦传输过滤器。

txfilter = comm.RaisedCosineTransmitFilter(。。。'RolloffFactor',0.2,。。。“ Filterspaninsymbols”,8,。。。'OutputSamplesPerSymbol',sps);

克雷亚te a phase frequency offset object to introduce the 4 kHz frequency offset.

freqOffset = comm.PhaseFrequencyOffset(。。。“频率offset”,-4000,。。。'采样率',fs);

克雷亚te a coarse frequency compensator object to compensate for the offset.

freqComp = comm.CoarseFrequencyCompensator(。。。'Modulation','QPSK',。。。'采样率',fs,。。。“频率分辨”,1);

生成QPSK符号，过滤调制数据，通过AWGN通道传递信号，然后应用频率偏移。

data = randi([0 3],nSym,1); modData = pskmod(data,4,pi/4); txSig = txfilter(modData); rxSig = awgn(txSig,20,“测量”）；offsetData = freqoffset（rxsig）;

Compensate for the frequency offset using the coarse frequency compensator. When the frequency offset is high, applying coarse frequency compensation prior to receive filtering is benefitial because filtering suppresses energy in the useful spectrum.

[ERSSEDDATA，ESTFREQOFFSET] = FREQCOMP（OFFSETDATA）;

Display the estimate of the frequency offset.

estFreqOffset

estFreqOffset = -4.0001e+03

Return information about the coarse frequency compensator System object. To obtain the FFT length, you must call coarse frequency compensator System object prior to calling theinfoobject function.

freqcompinfo =info(freqComp)

freqcompinfo =struct with fields:FFTLength: 131072 Algorithm: 'FFT-based'

创建一个频谱分析仪对象并绘制偏移和补偿光谱。验证补偿信号在0 Hz时具有中心频率，并且偏移信号的中心频率为-4 kHz。

specAnal = dsp.SpectrumAnalyzer('采样率',fs,'ShowLegend',true,。。。“频道名称”,{'Offset Signal','Compensated Signal'}); specAnal([offsetData compensatedData])

Figure Spectrum Analyzer contains an axes object and other objects of type uiflowcontainer, uimenu, uitoolbar. The axes object contains 2 objects of type line. These objects represent Offset Signal, Compensated Signal.

Compensate for Frequency Offset Using Coarse and Fine Compensation

Open Live Script

使用载体同步器在嘈杂的QAM信号中纠正相位和频率偏移。然后使用载体同步器和粗频薪补偿器校正偏移量。

Set the example parameters.

fs = 10000;% Symbol rate (Hz)sps = 4;% Samples per symbolM = 16;% Modulation orderk = log2(M);% Bits per symbolEbNo = 20;% Eb/No (dB)SNR = convertSNR(EbNo,"ebno",BitsPerSymbol=k,SamplesPerSymbol=sps);

克雷亚te a constellation diagram object to visualize the effects of the offset compensation techniques. Specify the constellation diagram to display only the last 4000 samples.

constdiagram = comm.constellationdiagram（。。。“参考结构化”，Qammod（0：M-1，M），。。。“ Samplespersymbol”,sps,。。。“符号StodisPlaySource”,'财产',。。。'SymbolsToDisplay'，4000，。。。'XLimits',[-5 5],。。。'YLimits',[-5 5]);

Introduce a frequency offset of 400 Hz and a phase offset of 30 degrees.

phaseFreqOffset = comm.PhaseFrequencyOffset(。。。“频率offset”,400,。。。'PhaseOffset',30,。。。'采样率',fs);

生成随机数据符号并应用16 QAM调制。

data = randi（[0 M-1]，10000,1）;modsig = qammod（data，m）;

克雷亚te a raised cosine filter object and filter the modulated signal.

txfilter = comm.RaisedCosineTransmitFilter(。。。'OutputSamplesPerSymbol',sps,。。。'Gain'，SQRT（SPS））;txsig = txfilter（modsig）;

Apply the phase and frequency offset, and then pass the signal through the AWGN channel.

freqOffsetSig = phaseFreqOffset(txSig); rxSig = awgn(freqOffsetSig,SNR);

通过使用载体同步器对信号进行良好的频率校正。

fineSync = comm.CarrierSynchronizer(。。。'阻尼因子',0.7,。。。“标准化卢比窗口”，0.005，。。。“ Samplespersymbol”,sps,。。。'Modulation','QAM'）；rxData = fineSync(rxSig);

Display the constellation diagram of the last 4000 symbols.

constdiagram(rxData)

Even with time to converge, the spiral nature of the plot shows that the carrier synchronizer has not yet compensated for the large frequency offset. The 400 Hz offset is 1% of the sample rate.

Repeat the process with a coarse frequency compensator inserted before the carrier synchronizer.

克雷亚te a coarse frequency compensator to reduce the frequency offset to a manageable level.

coarseSync = comm.CoarseFrequencyCompensator(。。。'Modulation','QAM',。。。“频率分辨”，1，。。。'采样率'，fs*sps）;

Pass the received signal to the coarse frequency compensator and then to the carrier synchronizer.

syncoarse = coarsync（rxsig）;rxData = finesync（Synccoarse）;

Plot the constellation diagram of the signal after coarse and fine frequency compensation. The received data now aligns with the reference constellation.

constdiagram(rxData)

Algorithms

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基于相关的估计

使用基于相关的估计算法来估计PSK和PAM信号的频率偏移。为了确定频率偏移，ΔF, the algorithm performs a maximum likelihood (ML) estimation of the complex-valued oscillationexp(j2πΔft), as described in[1]。这observed signal,r_k，表示为

$r_{k} = e^{j (2 π δ f k T_{s} + θ)}, 1 \leq k \leq N$

T_s是采样间隔，θis an unknown random phase, andN是样本的数量。频率偏移的ML估计等同于寻求可能性函数的最大值，

$λ (δ f) \approx {| \sum_{i = 1}^{N} r_{i} e^{- j 2 π δ f i T_{s}} |}^{2} = \sum_{k = 1}^{N} \sum_{m = 1}^{N} r_{k} r_{m}^{*} e^{- j 2 π δ f T_{s} (k - m)}$

简化后，问题表示为离散的傅立叶变换，由抛物线窗口函数加权。它表示为

$Im {\sum_{k = 1}^{N - 1} k (N - k) R (k) e^{j 2 π δ \hat{f} T_{s}}} = 0$

R(k)denotes the estimated autocorrelation of the sequencer_kand is represented as

$R (k) ≜ \frac{1}{N - k} \sum_{i = k + 1}^{N} r_{i} r_{i - k}^{*}, 0 \leq k \leq N - 1$

期限k (n - k)is the parabolic windowing function. In[1], it is shown thatR(k)is a poor estimate of the autocorrelation ofr_k什么时候k= 0或何时k接近N。因此，窗口函数可以表示为1S的矩形序列k= 1, 2, ...,L，在哪里L≤N- 1.结果是修改后的ML估计策略，其中

$Im {\sum_{k = 1}^{L} R (k) e^{- j 2 π δ \hat{f} k T_{s}}} = 0$

This equation results in an estimate of $δ \hat{f}$ in which

$δ \hat{f} ≅ \frac{f_{s a m p}}{π (L + 1)} \arg {\sum_{k = 1}^{L} R (k)}$

采样频率，f_samp, is the reciprocal ofT_s。这number of elements used to compute the autocorrelation sequence,L, are determined as

$L = 圆形的 (\frac{f_{s a m p}}{f_{m a x}}) - 1$

f_maxis the maximum expected frequency offset. and圆形的is the nearest integer function. The frequency offset estimate improves whenL≥ 7并提出建议f_max≤f_samp/ (4M)。

基于FFT的估计

基于FFT的估计算法可用于估计所有调制类型的频率偏移。这comm.CoarseFrequencyOffset系统对象uses two variations.

Forbpsk,QPSK,8psk,PAM, orQAM调制，comm.CoarseFrequencyOffset系统对象uses the FFT-based algorithm described in[2]。算法估计值 $δ \hat{f}$ by using a periodogram of them^th接收信号的功率，并给出

$δ \hat{f} = \frac{f_{s a m p}}{N Å m} \arg \max_{f} | \sum_{k = 0}^{N - 1} r^{m} (k) e^{- j 2 π k t / N} |, (- \frac{R_{s y m}}{2} \leq f \leq \frac{R_{s y m}}{2})$

wherem是调制顺序，r(k)是接收的序列，R_符号是符号率，并且N是样本的数量。这algorithm searches for a frequency that maximizes the time average of them接收信号的功率乘以[ -R_符号/2，R_符号/2]. Because the form of the algorithm is the definition of the discrete Fourier transform ofr^m(t)，搜索最大化时间平均的频率等同于在频谱中搜索峰值线r^m(t)。FFT要求的点数是

$N = 2^{⌈ {日志}_{2} (\frac{f_{s a m p}}{f_{r}}) ⌉}$

wheref_ris the desired frequency resolution.
对于OQPSK调制，comm.CoarseFrequencyOffset系统对象uses the FFT-based algorithm described in[4]。该算法在符号速率周围搜索±200 kHz的光谱峰。该技术在由于滤波引起的基带频率周围的光谱含量中存在干扰而定位所需的峰。

参考

[1] Luise，M。和R. Reggiannini。“爆发模式传输的全数字调制解调器中的载波频率恢复。”IEEE^®Transactions on Communications，卷。43，不。2/3/4，1995年2月，第1169–78页。

[2] Wang, Y., et al. “Non-Data-Aided Feedforward Carrier Frequency Offset Estimators for QAM Constellations: A Nonlinear Least-Squares Approach.”EURASIP Journal on Advances in Signal Processing，卷。2004, no. 13, Dec. 2004, p. 856139.

[3] Nakagawa, Tadao, et al. “Non-Data-Aided Wide-Range Frequency Offset Estimator for QAM Optical Coherent Receivers.”Optical Fiber Communication Conference/National Fiber Optic Engineers Conference 2011, OSA, 2011, p. OMJ1.

[4] Olds, Jonathan.Designing an OQPSK demodulator。

扩展功能

C/C ++代码生成
Generate C and C++ code using MATLAB® Coder™.

用法注释和限制：

SeeSystem Objects in MATLAB Code Generation（MATLAB编码器）。

Version History

Introduced in R2015b

Comm.CoarseFrequencyCompensator

描述

创建

Syntax

描述

特性

`调制`—调制type
`'QAM'`（默认）|`'8psk'`|`'bpsk'`|`'OQPSK'`|`'PAM'`|`'QPSK'`

`Algorithm`—Algorithm used to estimate frequency offset
`'FFT-based'`（默认）|`“基于相关”'`

Dependency

`FrequencyResolution`—Frequency resolution
`0.001`（默认）|positive scalar

`最大频率OFFENDSET`—Maximum measurable frequency offset
`0.05`（默认）|positive scalar

Dependency

`采样率`—Sample rate
`1`（默认）|positive scalar

`Samplespersymbol`—Samples per symbol
`4`（默认）|即使是整数,大于或等于`4`

Dependency

Usage

Syntax

描述

Input Arguments

`x`—输入信号
column vector

输出参数

`y`— Compensated output signal
complex column vector

`estimate`- 频率偏移的估计值
scalar

Object Functions

特定于`Comm.CoarseFrequencyCompensator`

Common to All System Objects

例子

Compensate for Frequency Offset in QPSK Signal

Compensate for Frequency Offset Using Coarse and Fine Compensation

Algorithms

基于相关的估计

基于FFT的估计

参考

扩展功能

C/C ++代码生成
Generate C and C++ code using MATLAB® Coder™.

Version History

See Also

Objects

块

Comm.CoarseFrequencyCompensator

描述

创建

Syntax

描述

特性

调制—调制type'QAM'（默认）|'8psk'|'bpsk'|'OQPSK'|'PAM'|'QPSK'

Algorithm—Algorithm used to estimate frequency offset'FFT-based'（默认）|“基于相关”'

Dependency

FrequencyResolution—Frequency resolution0.001（默认）|positive scalar

最大频率OFFENDSET—Maximum measurable frequency offset0.05（默认）|positive scalar

Dependency

采样率—Sample rate1（默认）|positive scalar

Samplespersymbol—Samples per symbol4（默认）|即使是整数,大于或等于4

Dependency

Usage

Syntax

描述

Input Arguments

x—输入信号column vector

输出参数

y— Compensated output signalcomplex column vector

estimate- 频率偏移的估计值scalar

Object Functions

特定于Comm.CoarseFrequencyCompensator

Common to All System Objects

例子

Compensate for Frequency Offset in QPSK Signal

Compensate for Frequency Offset Using Coarse and Fine Compensation

Algorithms

基于相关的估计

基于FFT的估计

参考

扩展功能

C/C ++代码生成Generate C and C++ code using MATLAB® Coder™.

Version History

See Also

Objects

块

`调制`—调制type
`'QAM'`（默认）|`'8psk'`|`'bpsk'`|`'OQPSK'`|`'PAM'`|`'QPSK'`

`Algorithm`—Algorithm used to estimate frequency offset
`'FFT-based'`（默认）|`“基于相关”'`

`FrequencyResolution`—Frequency resolution
`0.001`（默认）|positive scalar

`最大频率OFFENDSET`—Maximum measurable frequency offset
`0.05`（默认）|positive scalar

`采样率`—Sample rate
`1`（默认）|positive scalar

`Samplespersymbol`—Samples per symbol
`4`（默认）|即使是整数,大于或等于`4`

`x`—输入信号
column vector

`y`— Compensated output signal
complex column vector

`estimate`- 频率偏移的估计值
scalar

特定于`Comm.CoarseFrequencyCompensator`

C/C ++代码生成
Generate C and C++ code using MATLAB® Coder™.