基于瞬时频率的FSK信号解调研究

比较常用的FSK信号解调方法有频率推算、相位推算,可以解调出信号的两个频率,用FFT和ZFFT检测信号的调制频率,此方案的缺点是只有在信噪比较高时才能达到精度要求。文章研究了一种新的解调方案,把希尔伯特-黄变换算法引入到FSK信号的解调之中。通过改进算法,只需用IMF1(第一个本征模态函数)的瞬时频率即可检测出FSK信号的载频和调制频率。仿真结果显示,即使在信噪比为1∶3甚至更低的情况下,希尔伯特-黄变换算法的解调精度仍然高于以往的算法。     

Kernel estimation of the instantaneous frequency

Considers kernel estimators of the instantaneous frequency of a slowly evolving sinusoid in white noise. The expected estimation error consists of two terms. The systematic bias error grows as the kernel halfwidth increases while the random error decreases. For a nonmodulated signal g(t), the kernel halfwidth that minimizes the expected error is proportional to h~[(σ²)/(N|∂_t² g|2)]^1/5 where σ² is the noise variance and N is the number of measurements per unit time. The author shows that estimating the instantaneous frequency corresponds to estimating the first derivative of a modulated signal, A(t)exp(iφ(t)). For instantaneous frequency estimation, the halfwidth which minimizes the expected error is larger: h_1,3~[(σ²)/(A²N|∂_t ³(e^iφ¯(t/))|sup 2/)]¹/$ u7. Since the optimal halfwidths depend on derivatives of the unknown function, the authors initially estimate these derivatives prior to estimating the actual signal     

Nonparametric estimation of instantaneous frequency

The local polynomial approximation of time-varying phase is used in order to estimate the instantaneous frequency and its derivatives for a complex-valued harmonic signal given by discrete-time observations with a noise. The considered estimators are high-order nonparametric generalizations of the short-time Fourier transform and the Wigner-Ville distribution. The asymptotic variance and bias of the estimates are obtained     

On the instantaneous frequency of cyclostationary random signal

Expressions are derived for the moments of instantaneous frequency of a cyclostationary random signal. It is shown that the cyclostationary signal is not only characterized by the periodicity of its statistical moments, but can also be characterized by the periodicity of the moments of its instantaneous frequency. The considerations set forth here are based mostly on the theory of cyclostationary signals developed by Gardner (1985)     

一种基于频率校正的BPSK信号高精度载频估计算法

为了实现BPSK信号载频的高精度估计,提出一种基于频率校正的高精度BPSK信号载频估计算法。算法通过非线性变换将BPSK信号的载频估计问题转化为对点频信号的估计,再用DFT对点频信号进行粗估计,针对DFT估计频率分辨率差的问题,采用相位差校正法对DFT估计频率进行校正,从而实现BPSK信号载频的高精度估计。最后,通过性能分析和计算机仿真验证了算法的有效性,其结果表明:该算法在低信噪比情况下能获得较好的估计精度,在高信噪比情况下,估计精度大幅提高。     

基于改进DFT相位差的正弦波频率估计

针对基于离散傅里叶变换( DFT)相位差的正弦波频率估计方法对频偏敏感的问题,提出了一种改进DFT相位差频率估计方法。首先推导了DFT相位差法频率估计的均方误差,然后提出了基于Rife插值的改进DFT相位差频率估计方法,较好地解决了正弦波频率估计对频偏敏感的问题。仿真实验结果表明,改进方法在各种频偏下均能取得较高的估计精度,估计性能接近克拉美罗限( CRLB)。     

Distribution of instantaneous frequency for signal plus noise

A concise formula is derived for the probability distribution of the instantaneous frequency of an arbitrary bandpass signal plus Gaussian noise. The results are presented in terms of Marcum'sQ-functions, with well-known properties. The results are applicable in the performance analysis ofn-ary FM and PM data transmission systems. Illustrative examples of the application of the formula are worked out for binary FSK.     

基于谱估计的噪声调频信号检测方法研究

对干扰信号的频谱特征进行精确测量和分析是实施有效的电子反干扰(ECCM)的重要步骤.通过对噪声调频干扰信号的频谱特征分析,提出采用合适的功率谱估计方法来检测噪声调频信号的主要频谱特征参数.利用MATLAB/Simulink仿真软件分别建立了噪声调频信号源和谱估计方法的系统模型,研究了系统采用不同的谱估计方法和参数设置的情况下所能够达到的检测精度,并根据仿真结果分析比较了不同谱估计方法的性能.     

基于时频矩阵局部对比度的跳频信号参数估计

为了提高低信噪比下跳频信号参数估计性能,提出了一种基于时频矩阵局部对比度的跳频信号参数估计算法。根据跳频信号和噪声的时频分布不同特点,利用时频矩阵在不同尺度滑窗下的局部能量对比值均值,得到多尺度局部能量对比特征矩阵,通过此特征矩阵和自适应阈值分离得到仅保留了跳频信号时频信息的时频矩阵P。然后从P中提取时频跳变信息,精确估计跳频信号的跳频周期、起跳时间和跳变频率。仿真结果表明,与传统局部对比度（local contrast measure,LCM）法及形态学滤波法相比,本文算法具有更好的跳频信号提取效果和更高的参数估计精度,其有效性与实用性在DSP+FPGA的硬件系统上得到了测试验证。     

Improved maximum frequency estimation with application to instantaneous mean frequency estimation of surface electromyography

The purpose of this study was to improve the maximum-frequency estimation. Three methods to estimate the maximum frequency of a bandlimited signal with additive white noise were compared. Two existing methods, the threshold-crossing method (TCM) and the hybrid method, were modified for time-frequency representations. A novel approach, the running-block threshold method (RBTM), was introduced. Based on calculation of detection probability (sensitivity) the RBTM improved the maximum-frequency estimate as compared with the TCM. The maximum-frequency estimation methods were also used to determine the integration interval for instantaneous mean-frequency (IMNF) estimation from synthesized surface electromyography containing white noise. Results showed that the IMNF estimate was improved by using any of the three methods and that the RBTM gave the best IMNF estimate.     

Statistical properties of the instantaneous frequency for a noisy signal

In this paper a comprehensive study of the statistical properties of the instantaneous frequency is presented. A rather crude estimate is given in the both situation where the signal to noise ratio tends respectively towards zero or infinity. For an intermediate state a more refined and exact computation, which recovers the asymptotic situations, has been performed. Two main results must be emphasized; the first deals with the bias of the instantaneous frequency and the second with the good immunity of this frequency against the noise.     

Auditory motivated level-crossing approach to instantaneous frequency estimation

We address the problem of estimating the instantaneous frequency (IF) of a phase signal using its level-crossing (LC) information based on front-end auditory processing motivation. We show that the problem of IF estimation using LC information can be cast in the framework of estimation from irregularly sampled data. The formulation has the generality of estimating different types of IF without the need for a quasistationary assumption. We consider two types of IF-polynomial and bandlimited; we use polynomial interpolating functions for the former, and for the latter, we propose a novel "line plus sum of sines" model. The model parameters are estimated by linear regression. Considering the noisy case, LC data for different levels is analyzed, and methods for combining different estimators from LCs are discussed. Theoretical and extensive simulation results show that the performance of the zero-crossing (ZC) based IF estimator and the level-crossing based IF estimator with smaller level values is better than those obtained with higher level values or their combinations. The new technique reaches the Crame/spl acute/r-Rao bound (CRB) roughly above 4 dB signal-to-noise ratio (SNR), and its performance does not deteriorate rapidly with mismatch in the IF order compared with the other techniques in the literature.     

2-D phase unwrapping and instantaneous frequency estimation

The phase of complex signals is wrapped since it can only be measured modulo-2π; unwrapping searches for the 2π-combinations that minimize the discontinuity of the unwrapped phase, as only the unwrapped phase can be analyzed and interpreted by further processing. Given an estimate of the phase gradient (i.e., of the instantaneous frequency), the 2-D unwrapped phase can be obtained as a solution of a variational problem. The analysis of unwrapping is done quite separately from instantaneous frequency estimation so that the reliability of both steps can be assessed independently. Various methods for evaluating 2-D instantaneous frequency are presented and compared in the presence of noise and amplitude variations. A study has also been made on aliasing arising in areas where, with respect to instantaneous frequency, spatial sampling is insufficient. The presence of noise in the data further complicates phase aliasing analysis since there is no way to distinguish between the aliasing due to noise or that due to steep phase slopes     

Viterbi algorithm for chirp-rate and instantaneous frequency estimation

An instance of the Viterbi algorithm has been applied to the cubic phase function and chirp-rate estimation. The proposed algorithm has shown excellent performance for high noise environment. The obtained chirp-rate estimate is used in the instantaneous frequency estimation. The proposed instantaneous frequency estimator gives superior performance with respect to the state-of-the-art techniques for signals with non-linear instantaneous frequency.     

An adaptive Generalized S-transform for instantaneous frequency estimation

The Generalized S-transform (GST) applied in Instantaneous Frequency (IF) estimation is addressed in this paper. The analytical model for IF estimation error using the GST is established, which reveals that the estimation bias is determined directly by two variables: the standard deviation of the Gaussian window and the Instantaneous Frequency Rate (IFR) of the test signal. Based on the mathematical model, performance of the GST as an IF estimator is analyzed by three steps. Firstly, the time-varying expression for IF estimation Relative Error (RE) using the GST is derived. Secondly, the relationships between the RE and the signal’s frequency characters are found. Thirdly, the effects of the window parameters on the RE are discussed. Consequently, a novel Adaptive Generalized S-transform (AGST) is developed, in which the window parameters are automatically adjusted in order to process signals with fast changing frequency characters. The proposed method is evaluated through several kinds of test signals to show its efficiency in IF estimation.     

一种基于CRS插值的频偏估计方法

针对正交频分复用系统对频率偏移异常敏感导致接收机无法正确解调信号的问题,提出了一种小区特定参考信号(Cell-special Reference Signal,CRS)改进的频偏估计方法。首先,对发送的CRS与接收的CRS进行互相关运算,得到信道估计值;然后,对CRS在频域进行插值,使得每个时隙中不同OFDM符号对应子载波位置的参考信号相同;最后,对两个不同OFDM符号中的参考信号部分进行相关性运算,求出频偏。与基于CRS的频偏估计方法相比,该方法用信道估计值做互相关运算,消除了噪声和多径干扰带来的影响;通过对CRS进行插值,提高了频偏估计精度;通过减小计算相关性的两OFDM符号间的距离,使频偏估计范围由\[-1 kHz,1 kHz\]扩大到\[-1.75 kHz,1.75 kHz\]。     

基于TSLPFT1-FFT的线性调频信号参数估计方法

线性调频信号(Liner Frequency Modulation,LFM)广泛应用于雷达、通信、地震勘测等领域,为了解决传统方法对其调频率和中心频率参数估计性能较差的问题,提出了基于一阶局部多项式傅里叶变换两级搜索( Two-stepSearch one-order Local Polynomial Fourier ...     

基于二进小波变换的实信号的多尺度Hilbert变换和瞬时频率提取

该文着重讨论了使用二进小波变换方法实现数字Hilbert滤波,特别是使用滤波器组实现多尺度Hilbert滤波所要考虑的各尺度滤波器的设计问题。将多尺度Hilbert方法应用到求信号的瞬时参数中,并利用小波变换的去噪思想,取得了比使用DWT方法去噪更好的去噪效果。     

基于CORDIC算法的数字瞬时测频

数字瞬时测频(DIFM)是现代雷达对抗中的关键技术之一,它要求在极短的时间要完成对输入信号频率的测量。传统的瞬时测频方法是将频率信息转化为相位信息,之后再把相位信息转化为幅度信息,通过对幅度信息的量化编码,从而得到输入信号的频率。文中提出的是基于下变频,CORDIC算法的相位计算和相位推算法的数字瞬时测频方法。CORDIC算法的相位计算避免了乘法器的使用,因此适合实际应用。通过仿真得知,该方法对于单频信号的频率测量精度高,瞬时性好的优点,特别适合现代电子战接收机数字瞬时测频的需求。     

An efficient lattice predictor algorithm for instantaneous frequency estimation

An efficient method for spectral analysis of non-stationary signals is proposed. The signals are modelled as time-varying autoregressive (AR) processes and the relevant AR parameters are obtained from the adaptive lattice predictor coefficients minimizing the forward/backward prediction errors. In this paper it is proposed to use the sign algorithm, which computes the pertinent coefficients using only the signs of the forward/backward prediction errors at each stage. This method requires less number of multiplications than other adaptive lattice predictor algorithms. The performance of this method is compared with that of the adaptive lattice predictor using the least mean square algorithm for the problems of estimating instantaneous frequencies of FM signals via computer simulations.