基于局部多项式傅里叶变换的多分量线性调频信号瞬时频率估计*

针对多分量线性调频信号的瞬时频率估计问题,把局部多项式傅里叶变换应用到求多分量线性调频信号瞬时频率估计中,提出了一种不受分量间交叉项干扰的新方法,该方法对多分量线性调频信号进行局部多项式傅里叶变换,把每一个线性调频信号分离出来,根据每一个线性调频信号的局部多项式傅里叶变换谱,通过搜索找到谱的峰值所在的位置,从而找到峰值所对应的频率,准确地估计出了多分量线性调频信号的瞬时频率。仿真实验中与多分量信号的Wigner-Hough变换进行了对比,验证了该方法的有效性。     

频率估计的一种多段同频等长信号频谱融合法

为提高信号频率估计精度和现有方法的普适性,提出一种基于频谱融合的多段同频等长信号的频率估计算法。设计相位差补偿因子克服分段信号相位不连续问题,以达到相位连续信号的频谱分析效果;建立搜索频率序列修正相位差补偿因子中的未知参数,并对分段信号频谱进行相位差补偿得到修正频谱矩阵;通过累积频谱抽取谱和修正频谱计算频谱相关序列并搜索最大值,其对应搜索频率即为该算法的频率估计值。数值仿真实验表明,基于该算法频率估计的均方根误差约为现有方法的1/4~2/3,较为接近Cramer-Rao下限。     

一种新的线性调频信号的瞬时频率估计方法*

基于HHT（HilbertHuang transformation）是一种能分解出信号的任何频率分量的主成分分析法以及线性调频信号（LFM）的瞬时频率是关于时间的直线,将LFM 信号先作HHT得到其瞬时频率,然后利用该瞬时频率中间部分的时频点作最小二乘（LSM）直线拟合。这种改进的LSM直线拟合方法不仅剔除了HHT固有的边界效应在瞬时频率斜线两端产生的高频谐波,从而有效地抑制了这种边界效应对瞬时频率估计的影响,而且直接得到了较为准确的LFM 信号的瞬时频率参数估计值。与通过改变HHT算法来减小HHT边界     

数字测频算法研究综述

介绍了目前比较常用的几种数字测频算法及其基本原理,并对其中的直接计数法、相位推算法、频率推算法、傅里叶变换法及谱估计等方法进行了MATLAB仿真研究.总结了各种算法的主要优缺点,为设计者选取合适的算法进行工程应用提供了参考.     

基于多段分频等长信号融合的频率估计方法

多段采样信号十分常见,对其进行信息融合能有效提高信号处理的精度,尤其适用于低信噪比、被测频率持续时间短的情况。为提高多段采样信号频率估计的精度和扩展已有方法的适用范围,给出一种多段分频等长信号融合方法。在该方法中,因各段信号的被测频率不等,故生成频域分析参数矩阵以实现同频化效果;因同频化后各段信号之间仍然相位不连续,故设计相位差补偿因子矩阵以达到相位连续信号的效果;因相位差补偿因子矩阵包含未知参数,故生成搜索频率序列以用于实际计算并得到具有特定形式的功率谱矩阵。为验证方法的正确性,给出了数学证明。针对多种应用环境状态进行了仿真实验,结果表明该方法具有普适性,抗噪性好,频率估计精度比现有方法有较大提高。     

频率选择性衰落信道下OFDM信噪比盲估计

针对频率选择性衰落信道下带有载波频偏的OFDM(正交频分复用)信号信噪比(SNR)估计问题,提出一种基于空载波OFDM系统的SNR盲估计方法.由于本振和接收信号之间的不一致,会使得接收到的信号带有一定的频偏.频偏的存在破坏了子载波间的正交性,增加了子载波间的干扰噪声,从而减少了SNR.首先分析了频偏对信噪比的影响并得到有无频偏时信噪比之间的关系,其次根据空载波的特点估计出无频偏时的信噪比,再基于上述关系对OFDM信号进行有频偏时的信噪比盲估计,最后通过仿真验证了理论分析的正确性.     

宽带混合信号的快速DOA估计算法

针对均匀线列阵,在宽带混合信号(不相关和相干信号共存)情形下,提出了一种DOA快速估计新算法。利用阵列协方差矩阵的Hermitian性,通过酉变换将各频点的复数据矩阵映射为实矩阵,通过实值化的TOFS法先直接估计出宽带非相关信号的DOA;然后利用空间差分技术,在各个频点上得到只含相干信号的数据协方差矩阵;通过Toeplitz矩阵重构,在不降低阵列孔径的条件下,可实现相干信号的解相干,再利用实值TOFS法可得到相干信号的DOA。由于算法是并行分别对不相关和相干信号进行DOA估计,在信源过载(信号数大于阵元数)的情形下,算法依然有效,同时由于实值化,算法的计算复杂度较小。仿真结果验证了算法的有效性。     

一种基于循环谱的MPSK信号符号速率估计方法*

针对频谱感知的实际应用,在循环平稳理论的基础上,研究了经过脉冲成形滤波器滤波后的MPSK信号的循环谱特性,通过分析有限数据条件下剩余带宽对循环谱估计的影响,提出一种恒包络处理与频域平滑循环周期图结合的符号速率估计算法,仿真表明该方法在有限数据条件下具有良好的性能,而且在剩余带宽较小时,该方法也能有效地估计MPSK信号的符号速率。     

信号等长情况下频率估计的分频域迭代分析法

从特征识别角度分析了现有频率估计方法的信号分解结构的特点,并提出了一种分频域分解结构,将对应不同时间的多个单频信号融合构成一个组合信号,以利用时域已知信息并形成信息积累作用,能有效抑制干扰频率和削弱冲击噪声且计算量增加较少。为配合分频域分解结构的使用和提高分析过程的实时性,采用了分频等长融合算法和间接迭代计算,并进行了方法正确性的数学证明。针对多种应用环境状态进行了仿真实验,结果表明该方法抗噪性和实时性较好,频率估计精度比现有方法有较大提高。     

基于改进WVD的跳频信号参数估计方法

为了克服传统的平滑伪魏格纳分布(SPWVD)在跳频信号参数估计中分辨率降低的问题,提出基于改进WVD算法的跳频信号参数估计新方法。通过分析跳频信号WVD的性质和特点,构造出与跳频信号WVD自项支撑区重合的时频窗,用其与信号WVD相乘进行加窗,有效抑制交叉干扰项的同时保持了WVD良好的时频分辨率,得到了清晰的跳频信号时频分布,基于此分布给出跳频信号参数估计的具体步骤。仿真实验结果表明,该方法有效可行且具有很好的整体性能。     

基于FRFT的多分量LFM信号DOA估计

提出了一种基于分数阶Fourier变换的多分量LFM信号波达方向估计算法。观测信号经滤波和解线调处理,变换为一系列单频平稳信号。在分数阶Fourier域结合传统的MUSIC算法,从而实现了LFM信号的方向估计。给出了估计误差的统计分析,使得这一方法在理论上趋于完备,仿真试验验证了算法的有效性。     

Wideband beamforming for multipath signals based on frequency invariant transformation

It is well known that the performance of conventional adaptive beamformers degrades severely due to the presence of coherent or correlated interferences(multipath propagation) and various techniques have been developed to improve the performance of the beamformer.However,most of the work in the past has been focused on the narrowband case.In this paper,the wideband beamforming problem in the presence of multipath signals is addressed,with a novel approach proposed by employing a pre-processing stage based on the frequency invariant beamforming(FIB) technique.In this approach,the received wideband array signals are first processed by an FIB network,and then a traditional narrowband adaptive beamformer or an appropriate instantaneous blind source separation(BSS) algorithm can be applied to the network outputs.It is shown that with the proposed structure,cancellation of the desired signal is reduced,leading to a significantly improved output signal to interference plus noise ratio(SINR).     

Fuzzy methodology for frequency response estimation of uncertain dynamic systems

Fuzzy frequency response: definition and analysis for uncertain dynamic systems is proposed in this paper. In terms of transfer function, the uncertain dynamic system is partitioned into several linear sub‐models and organized according to Takagi–Sugeno fuzzy representation. The main contribution of this paper is to demonstrate through the proposal of a Theorem that fuzzy frequency response is a boundary in the magnitude and phase Bode plots. Low‐ and high‐frequency analysis of fuzzy dynamic model is obtained by varying the frequency ω from zero to infinity. Copyright © 2011 John Wiley & Sons, Ltd.     

一种基于功率谱估计的盲载频估计新算法

信号载波频率估计是通信、雷达、声纳以及电子对抗等领域信号处理中的一个重要问题,将经典的载频估计算法——频率居中法与Welch功率谱估计算法相结合,提出一种改进的盲载频估计新算法。该算法无须信号的调制类别和定时信息即可实现信号的盲载频估计,在短波信道的仿真环境下,其低信噪比下的估计性能要优于频率居中法。即使在恶劣的短波信道环境下,该算法仍可实现对载频较为精确的估计,在短波通信中有着良好的应用前景。     

OFDM信号循环谱分析及参数估计*

针对在无线电监测和认知无线电系统中,信号参数估计这一重要问题,证明了OFDM信号具有循环平稳性的必要条件是加循环前缀或有非矩形脉冲成型,并以线性周期时变变换(LPTV)模型为基础,推导了OFDM信号的循环谱表达式。通过对连续信号和离散信号进行计算机仿真,都得到了相同的OFDM信号循环谱图,实现了OFDM信号符号周期的估计,结果与理论分析相吻合。     

基于听觉外围模型的音频基频估计方法

针对音频信号中的暂态成分对基频检测可靠性的影响,提出了一种基于听觉外围模型的基频估计方法。该方法根据听觉外围模型来模拟声音在人耳内耳听觉神经上传导过程,并利用循环平均幅度差函数判断每个神经传导信号上呈现的时域周期性,进而提取音频信号的基频。实验结果表明,在纯净音频条件下,该方法能准确地估计出音频信号的基频,并且在不同音量打击乐信号的干扰下,所提方法的平均错误率低于三种参考方法。     

Controlled-coverage discrete S-transform (CC-DST): Theory and applications

The S-transform (ST) is a popular linear time-frequency (TF) transform with hybrid characteristics from the short-time Fourier transform (STFT) and the wavelet transform. It enables a multi-resolution TF analysis and returns globally referenced local phase information, but its expensive computational requirements often overshadow its other desirable features. In this paper, we develop a fully discrete ST (DST) with a controllable TF sampling scheme based on a filter-bank interpretation. The presented DST splits the analyzed signal into subband channels whose bandwidths increase progressively in a fully controllable manner, providing a frequency resolution that can be varied and made as high as required, which is a desirable property for processing oscillatory signals lacked by previously presented DSTs. Thanks to its flexible sampling scheme, the behavior of the developed transform in the TF domain can be adjusted easily; with specific parameter settings, for example, it samples the TF domain dyadically, while by choosing different settings, it may act as a STFT. The spectral partitioning is performed through asymmetric raised-cosine windows whose collective amplitude is unitary over the signal spectrum to ensure that the transform is easily and exactly invertible. The proposed DST retains all the appealing properties of the original ST, representing a local image of the Fourier transform; it requires low computational complexity and returns a modest number of TF coefficients. To confirm its effectiveness, the developed transform is utilized for different applications using real-world and synthetic signals.     

低信噪比下跳频信号参数盲估计

针对通信对抗的实际应用,提出了一种在低信噪比下估计跳频信号跳速的方法。首先利用谱图的无交叉干扰项和修正平滑伪Wigner-Vile分布（MSPWD）的强时频聚集性,将谱图和MSPWD进行组合得到了清晰稳健的时频分布;然后基于此分布,利用二次差分法沿着频率轴搜寻每个时间的峰值显示来校正时频矩阵;根据此时频矩阵,分别利用FFT方法、自适应门限法、代价函数法来进行跳频周期估计,仿真结果显示,时频分布经过二次差分处理后,在更低信噪比下提高了估计精度,在跳速较低时,FFT方法在低信噪比时性能较好,在跳速较高时,代价函数法性能较好。     

Closed-form solution to motion parameter estimation of an acoustic source exploiting Doppler effect

This paper proposes an analytical solution for the parameter estimation of a moving acoustic source from the instantaneous frequency of a recorded signal on a ground located microphone. The acoustic source could be either a propeller-driven aircraft or a helicopter. During the transit of such acoustic source, the Doppler effect is exploited to estimate the speed, altitude, source frequency and the closest point of approach (CPA) time between the source and the microphone. The proposed solution is an original workout of an existing time–frequency based approach which has been applied previously to localize a propeller-driven aircraft. In contrast to existing solutions, the main advantage of the proposed one is the direct estimation of the flight parameters without resorting to any iterative procedure. The proposed approach is faster, less complex and therefore a good candidate for hardware implementation. The proposed solution is compared with respect to the existing approach in term of parameter estimation, performance and computation complexity. Experimental validations of the proposed solution are also presented.     

Direct synthesis of pseudo-random ternary perturbation signals with harmonic multiples of two and three suppressed

This paper proposes an analytical method to directly synthesise pseudo-random ternary perturbation signals for the identification of frequency response functions, through the multiplication of two components signals which satisfy a prescribed set of properties. The ternary signals generated have harmonic multiples of two and three suppressed; this specification is useful for reducing the effects of nonlinear distortion on the linear estimate. The signals have uniform magnitude in all, except two, of the nonzero harmonics. The method is significant in overcoming the existing problem of sparsity in the available periods when analytical methods are used, as well as the relatively long computational time required in approaches based on exhaustive search or computer optimisation. The proposed technique presents a breakthrough as it eliminates the sequence-to-signal conversion stage required in the existing conventional methods. A direct consequence is the increased signal power within amplitude constraints, which now equals the theoretical limit for the specification considered. If it is necessary to further increase the number of available periods, the mathematical derivation can be extended to a class of suboptimal direct synthesis signals; however, these possess reduced signal power compared with direct synthesis signals.