Analysis of the frequency domain adaptive filter

The purpose of this note is to demonstrate significant analytical simplifications for studying the behavior of adaptive filtering in the frequency domain as opposed to studying the behavior of adaptive filtering in the time domain. A closed form expression, for the single complex weight in the frequency domain adaptive filter, is presented which allows significant statistical analysis to be performed. The mean-square error of the filter is evaluated as a function of the algorithm step size and the signal and noise powers.     

能量分布识别相位畸变的自适应双域滤波方法

在基于能量分布识别相位畸变方法中,条纹图像的质量是影响畸变识别精度的主要因素之一。为了准确辨别条纹相位畸变,需对条纹图像进行滤波处理,滤除图像中的噪声以及背景信息等。提出了一种基于能量分布的自适应图像滤波方法,通过傅里叶变换将图像转换为能量分布图,根据畸变与未畸变图像能量弥散度差值大小对小波滤波的阈值进行调整,旨在寻求能量弥散度差值最大的阈值作为针对当前图像的滤波方法可接受阈值。通过对单空域、单频域以及双域滤波方法进行实验验证,结果表明单一使用空域或频域滤波处理,畸变图像与未畸变图像能量分布差别在1.4 %~3.2 %,使用非自适应双域滤波方法进行滤波处理,能量分布差别在7 %以上,而采用自适应双域滤波方法进行滤波处理,能量分布差别超过8 %。自适应双域滤波方法显著提高了能量的识别精度。     

DSSS通信中基于快速更新子带自适应滤波的窄带干扰抑制

本文面向直接序列扩频(DSSS)通信中的窄带干扰抑制,将分块更新子带自适应滤波的高频谱分隔特性和直接变换自适应滤波的逐点更新特性结合起来,提出了一种快速更新子带自适应(FRSAF)算法,给出了算法的迭代因子收敛界和快速实现结构。理论分析表明：该算法收敛迅速、迭代稳健,其性能明显优于经典子带自适应滤波算法和DCT/DFT-LMS算法,应用于DSSS通信可以得到优良的干扰抑制效果。仿真结果验证了上述结论。     

Spectral analysis of subband adaptive digital filters

Subband adaptive digital filters at stationary points are analyzed in the frequency domain. Approximate expressions for the optimal subband filters are presented, and then, a spectral representation of the error variance is derived. These are expressed in the frequency domain and, hence, enable us to see the aliasing effects in subband adaptive filtering     

一种中频抗窄带干扰自适应滤波方法

根据实际的技术需求,针对信号传输带内可能存在领近频率的干扰,采用自适应滤波技术,抑制带内的窄带干扰。该方法是一种数字滤波方法,对中频时域信号进行A/D采样,通过FFT(快速傅里叶变换),变换为相应的离散频域信号,应用抗窄带干扰的自适应滤波算法,消除其频带内的窄带干扰,而同时基本保留有效信号,通过IFFT(反变换)将滤波后的频域信号转换为时域信号,并D/A输出。     

A new method for efficient convolution in frequency domain bynonuniform partitioning for adaptive filtering

By using block processing, partitioning, and fast Fourier transforms (FFTs), large filters perform efficiently in the frequency domain. For small processing delay the complexity can still be too large for implementation on a digital signal processor (DSP). A solution is to partition the filter into unequal-length subfilters. Application in adaptive filtering yields the nonuniform partitioned block frequency domain adaptive filter (NU-PBFDAF)     

雷达海杂波的频域处理

通过对杂波特性的分析,特别是风对频域特性影响的分析,给出了三坐标雷达海杂波的信号模型。对该模型中各个影响因素进行了简要的分析,得出了频域去杂是最为有效的方法。针对杂波频域特征,提出了自适应频域滤波的算法,并给出了仿真结果。     

一种空-频联合最优滤波的被动宽带检测方法

常规宽带能量检测在多目标、强干扰环境下输出信噪比(SNR)降低,检测性能大幅度下降。针对此问题,该文提出一种将子阵导向最小方差(STMV)宽带空域自适应波束形成与频域Eckart滤波结合的空-频联合最优滤波宽带检测方法。该方法首先通过子阵导向最小方差波束形成进行空间自适应处理,利用自适应波束形成的干扰抑制能力在空域实现最优滤波;然后通过最大似然估计实时估计信号和噪声的功率谱,构造Eckart滤波对自适应波束形成的输出分配不同权重进行加权滤波,从而实现频域信噪比最大化。所提方法通过空-频联合最优滤波,降低空域旁瓣干扰和频带内噪声的影响,使得输出信噪比最大,从而有效地改善目标宽带检测能力,提高被动声呐的宽带检测性能。仿真和试验数据处理结果验证了该方法的有效性。     

卫星导航用户机自适应滤波研究

基于GPS接收机自适应滤波应用分析,系统地研究了卫星导航用户机时域、空域和空时域自适应滤波技术,以及相应的设计方案。重点通过空时处理等效性分析,提出卫星导航用户机在当前时域数字滤波器和空域自适应调零天线研究基础上,根据区域卫星导航系统实际应用要求,将空时域次优处理和小型阵列最优处理作为重点研究方向。     

基于Gabor环滤波的纹理分割方法

针对纹理分割问题,提出了一种在频率域呈环形分布的Gabor滤波器组(Gabor环)的设计方法,在能量意义下给出了自适应选择滤波环带的步骤,并给出了经Gabor滤波后纹理特征的计算公式。根据给定Gabor滤波器环具有的多方向特性对不同纹理图像进行滤波,然后计算滤波后各点特征,并利用这些多方向特征进行纹理分割。实验表明该方法能取得较好的分割效果,并具有很强的通用性。     

全相位DFT数字滤波器的一种等价结构

本文根据[1]中提出的全相位DFT数字滤波器的理论,导出了一种新型的频域网络结构。对于相同长度和频率响应的滤波器,该结构与[1]中的方案滤波效果相同,但运算量只有[1]的一半,硬件实现简单。由于可以直接得到梯度向量,因此可应用于自适应滤波领域,实验证明,它比传统的频域自适应滤波器具有更好的性能。     

Adaptive filtering in the frequency domain

Adaptive filtering in the frequency domain can be accomplished by Fourier transformation of the input signal and independent weighting of the contents of each frequency bin. The frequency-domain filter performs similarly to a conventional adaptive transversal filter but promises a significant reduction in computation when the number of weights equals or exceeds 16.     

非线性调频信号的自适应时频滤波算法

针对传统的时域或频域滤波算法对非线性调频信号滤波去噪效果不好的问题,本文提出了一种时频域内非线性调频信号的自适应滤波去噪算法。首先对原信号进行广义S变换获得其时频分布,接下来利用有效信号时频分布特性选取时频通域,构造区域滤波算子并去除掉时频通域外的噪声分量的时频分布;然后利用有效信号分量的时频聚集性构造自适应时频滤波算子,对含有随机噪声的有效信号分量进行滤波处理,得到滤波去噪后的信号的时频分布;最后利用广义S逆变换将处理后的时频分布变换到时间域,得到滤波去噪后的信号。通过仿真实验的结果可知,本文提出的算法在非线性调频信号的滤波去噪和有效特性保持方面取得了较好的效果。      

Frequency domain set membership fast normalised LMS adaptive algorithm

The concept of set membership (SM) adaptive filtering is extended to the frequency domain and a novel frequency domain SM algorithm is derived. Simulations show that the new SM algorithm has a much improved convergence rate over the conventional fast normalised least mean square (FNLMS) algorithm with identical misadjustment performance. Moreover, the SM algorithm has the same order of computational complexity as the FNLMS algorithm.     

一种新的变换域自适应LMS滤波算法

为了改善时变系统中的LMS算法收敛速度,一般可以在变换域进行自适应处理。通过研究和分析分数阶傅里叶变换与时-频平面的关系,提出在分数阶傅里叶变换域进行自适应时-频滤波。所提出的方法首先搜索最佳变换域,然后在分数阶傅里叶变换域进行LMS自适应滤波。仿真结果表明,与目前一些基于变换域的方法对比,新方法通过对时-频平面的旋转,可以显著加速算法收敛性。     

基于二进小波变换自适应Kalman滤波反褶积

本文提出了基于二进小波变换自适应Kalman滤波反褶积(AKFD)新方法.它抛弃了传统预测反褶积对信号平稳性的假设,克服了提高分辨率反而明显降低信噪比的矛盾,其较好地压缩反射波形,但噪声并没有明显提高,所以具有很好的抗噪性能.在小波域进行的AKFD压制假反射比在时间域AKFD好,此外,该方法具有对信号分频进行AKFD的特性,增强了Kalman滤波的自适应性,所以在小波域下的分辨率明显比在时域内高.同时,该方法克服了在时域内进行的AKFD抬升低频成份的缺陷.经大量的模型及实际资料处理表明该方法具有明显的效果.     

Adaptive arrays with main beam constraints

Initial applications of adaptive array theory to the radar sidelobe jamming problem ignored the problem of incidental cancellation of the desired signal returns. In more recent applications, longer transmitted waveforms have combined with returns from extended clutter and/or strong targets to create a more serious signal cancellation problem. There are several ways in which the adaptive processor can be constrained from responding to desired main lobe target returns while maintaining good cancellation of interference in the sidelobes. This paper examines the major techniques for constraining the response of the adaptive processor, including methods of controlling the response of the array in the absence of external interference. Time domain and frequency domain techniques are discussed. The majority of the discussion is devoted to angle domain techniques such as pilot signals, preadaption spacial filtering, and control loop spatial filtering. Analysis is presented showing the relationship between these techniques. Finally, examples are given showing the effects of these constraints as well as control of the quiescent array pattern.     

Acoustic echo-canceler using the FBAF algorithm

An acoustic echo-canceler for teleconferencing systems is realized based on the frequency bin adaptive filtering (FBAF) algorithm. In the FBAF algorithm, each frequency bin does an independent adaptive filtering, so that parallel processing can be used to increase the throughput of the system. Hardware size can be reduced to about 25% of the FIR time domain adaptive filter (TDAF) requirement. The realized echo canceler allows a comfortable conversation with only 8 ms of delay. The hardware prototype contains 12 VSP chips and one DSP chip, An ERLE (echo return loss enhancement) of 30 dB was achieved using this prototype hardware for an echo reverberation path with 260 ms delay. An efficient method for normalizing the convergence factor of the FBAF algorithm with a correlated input signal is given that speeds up the convergence rate. The performance is shown by computer simulation     

结合频域显著性分析和形态学滤波的红外小目标检测算法北大核心CSCD

针对复杂背景下的红外小目标检测问题,提出了基于频域显著性分析和形态学滤波相结合的图像处理算法。通过构建图像频域显著性分析图,并引入自适应阈值实现显著图的分割,提取感兴趣区域(ROI)以确定候选目标,达到凸显目标并抑制背景的目的。为抑制残余的杂波干扰,基于候选目标轮廓尺寸自适应并引入新的评价机制实现滤波结构元的筛选,采用新型Top-hat滤波技术消除伪目标响应。本算法充分利用红外小目标的频域显著性和空域尺寸先验信息的互补性实现检测,在设计中则平衡了计算复杂度与处理效果的矛盾关系,在有效提升检测指标的同时保证了实时计算的工程需求。实验表明本文提出的算法能显著提高目标信噪比,高效和准确地检测噪声背景下的弱小红外目标。     

On the complexity of frequency-domain adaptive filtering

In frequency-domain adaptive filtering (FDAF), the `crossover point' where the frequency domain becomes more efficient than the time domain is asymptotically 1.5 times as high for a DSP software realization as for a VLSI hardware realization. However, actual software realizations of FDAF may require as much as twice the computation predicted by theory, depending on the processor chosen. The approach can be extended to analyze other FDAF structures, such as multirate filters