HOS-based image sequence noise removal.

In this paper, a new spatiotemporal filtering scheme is described for noise reduction in video sequences. For this purpose, the scheme processes each group of three consecutive sequence frames in two steps: 1) estimate motion between frames and 2) use motion vectors to get the final denoised current frame. A family of adaptive spatiotemporal L-filters is applied. A recursive implementation of these filters is used and compared with its nonrecursive counterpart. The motion trajectories are obtained recursively by a region-recursive estimation method. Both motion parameters and filter weights are computed by minimizing the kurtosis of error instead of mean squared error. Using the kurtosis in the algorithms adaptation is appropriate in the presence of mixed and impulsive noises. The filter performance is evaluated by considering different types of video sequences. Simulations show marked improvement in visual quality and SNRI measures cost as well as compared to those reported in literature.     

Effect of substrate dielectric anisotropy on the frequency behaviorof microstrip circuits

In this paper, we carry out a full-wave analysis of shielded two-port microstrip circuits, in which the metallizations are embedded in a multilayered substrate that may contain isotropic dielectrics and/or anisotropic dielectrics. The Galerkin's method in the spectral domain is applied for determining the current density on the metallizations of the circuits when their feeding lines are excited by means of delta-gap generators, and the matrix pencil technique is subsequently used for deembedding the scattering parameters from the computed current densities. Results are presented for the scattering parameters of some microstrip discontinuities and filters printed on both isotropic dielectric substrates and anisotropic dielectric substrates. These results show that when substrate dielectric anisotropy is ignored, errors arise when computing the scattering parameters of microstrip discontinuities and when predicting the operating frequency band of microstrip filters     

Delayless method to generate current reference for active filters

Active power filters are used to eliminate AC harmonic currents by injecting equal but opposite compensating currents. Successful control of active filters requires, among other things, an accurate current reference. In this paper, we introduce a multistage adaptive filtering system which generates the current reference delaylessly and accurately. Our filter structure combines a low-pass prefilter and an adaptive predictive filter, making it possible to extract the sinusoidal active current from the distorted waveform without harmful phase shift, even when the frequency and amplitude alter simultaneously. Although active filters are typically used to compensate for the supply harmonics, where the fundamental frequency remains almost constant, we will show that our filter structure can also be applied in applications where the frequency alters rapidly     

A method for design of Mth-band filters

The objective of this paper is to present a theory, constraints, and a design method for nonlinear-phase halfband and Mth-band filters. Based on a time-domain property, the constraints and properties in the frequency domain are derived. They are the generalization of the well-known conditions for linear-phase Mth-band filters. Having found all necessary conditions, we present the design method based on an eigenfilter that minimizes the mean-squared errors. The design method is also extended to the design of nonlinear-phase Mth-band filters with properties of R-regularity, or equiripple stopband attenuation, or impulse responses that have complex coefficients. Design examples of various Mth-band filters with different properties are presented, discussed, and compared with the linear-phase case     

A new design algorithm for two-band orthonormal rational filterbanks and orthonormal rational wavelets

We present a new algorithm for the design of orthonormal two-band rational filter banks. Owing to the connection between iterated rational filter banks and rational wavelets, this is also a design algorithm for orthonormal rational wavelets. It is basically a simple iterative procedure, which explains its exponential convergence and adaptability under various linear constraints (e,g., regularity). Although the filters obtained from this algorithm are suboptimally designed, they show excellent frequency selectivity. After an in-depth account of the algorithm, we discuss the properties of the rational wavelets generated by some designed filters. In particular, we stress the possibility to design “almost” shift error-free wavelets, which allows the implementation of a rational wavelet transform     

入射角对光量子阱束缚态影响的研究

为了探讨入射角对光量子阱传输特性的影响,用传输矩阵法计算了不同入射角对光量子阱结构的传输特性,得到了光量子阱能应用于多通道滤波和光开关的结论.结果表明,光子的束缚效应将导致频率的量子化,通过微小地改变入射角可改变束缚态的频率,且入射角的变化与束缚态频率的变化呈3次多项式关系.此结果为该结构实现多通道滤波和方位开关提供了理论依据,也为得到所需要的束缚态频率提供了理论基础.     

Synthesis of Nonseparable 3-D Spatiotemporal Bandpass Filters on Analog Networks

Linear cellular neural networks (CNNs) are capable of performing efficient spatiotemporal filtering operations as recursive infinite impulse response (IIR) filters. Particularly, linear CNNs can be characterized as a spatial frequency-dependent recursive temporal filter with complex coefficients. Based on a modified version of the CNN paradigm recently proposed by the authors, nonseparable spatiotemporal bandpass filters with tunable spatiotemporal passband volumes are synthesized. The filters reported here qualitatively resemble spatiotemporal receptive field models for the primary visual cortex. Numerical simulation results confirm the bandpass characteristics of our filtering network.      

Wavelets and time-frequency analysis

We present a selective overview of time-frequency analysis and some of its key problems. In particular we motivate the introduction of wavelet and wavelet packet analysis. Different types of decompositions of an idealized time-frequency plane provide the basis for understanding the performance of the numerical algorithms and their corresponding interpretations within the continuous models. As examples we show how to control the frequency spreading of wavelet packets at high frequencies using nonstationary filtering and study some properties of periodic wavelet packets. Furthermore we derive a formula to compute the time localization of a wavelet packet from its indexes which is exact for linear phase filters, and show how this estimate deteriorates with deviation from linear phase     

Quasi-periodic spatiotemporal filtering.

This paper presents the online estimation of temporal frequency to simultaneously detect and identify the quasiperiodic motion of an object. We introduce color to increase discriminative power of a reoccurring object and to provide robustness to appearance changes due to illumination changes. Spatial contextual information is incorporated by considering the object motion at different scales. We combined spatiospectral Gaussian filters and a temporal reparameterized Gabor filter to construct the online temporal frequency filter. We demonstrate the online filter to respond faster and decay faster than offline Gabor filters. Further, we show the online filter to be more selective to the tuned frequency than Gabor filters. We contribute to temporal frequency analysis in that we both identify ("what") and detect ("when") the frequency. In color video, we demonstrate the filter to detect and identify the periodicity of natural motion. The velocity of moving gratings is determined in a real world example. We consider periodic and quasiperiodic motion of both stationary and nonstationary objects.     

DFT扩展OFDM系统中降低信号峰均比的频域成型方法

OFDM(正交频分复用)技术的主要缺点之一是其发送信号具有较高的峰均比。DFT(离散傅里叶变换)扩展OFDM系统的发送方案可以有效降低信号的峰均比。在该系统中,频域成型方法不仅对系统有无码间干扰的特性和抗噪声性能有重要影响,而且对发送信号的峰均比也有重要影响。文中首先在加性高斯白噪声信道下推导了无码间干扰和接收机最大输出信噪比条件下发送频域成型函数及接收频域成型函数所要满足的条件,然后根据该条件设计了几种频域成型方法。仿真结果表明,频域成型方法能进一步有效降低发送信号的峰均比。     

Extended permutation filters and their application to edge enhancement.

Extended permutation (EP) filters are defined and analyzed. In particular, we focus on extended permutation rank selection (EPRS) filters. These filters are constrained to output an order statistic from an extended observation vector. This extended vector includes N observation samples and K statistics that are functions of the observation samples. The rank permutations from selected samples in this extended observation vector are used as the basis for selecting an order statistic output. We show that by including the sample mean in the extended observation vector, the filters exhibit excellent edge enhancement properties. We also show that several previously defined classes of rank-order-based edge enhancers (CS, LUM, and WMMR sharpeners) can be formulated as subclasses of EPRS filters. These sharpening subclasses are in addition to the smoothing subclasses, which include rank conditioned rank selection, permutation stack, and weighted order statistic filters. Thus, this novel class of filters provides a broad framework within which many rank-order-based smoothers and edge enhancers can be unified. Edge enhancement properties are developed and an L(n) norm EPRS filter optimization procedure is presented. Finally, extensive computer simulation results are presented, comparing the performance of EPRS and other sharpening filters in edge enhancement applications.     

Tunable FIR and IIR Fractional-Delay Filter Design and Structure Based on Complex Cepstrum

A cepstrum-based approach is proposed to design finite- and infinite-impulse-response (IIR) fractional-delay (FD) filters. The maximal-flatness criteria on frequency responses are formulated as a system of linear equations to solve the truncated complex cepstrum. The closed-form solutions to cepstrum sequences can be derived. Moreover, it is very attractive that the resultant cepstrum coefficients are directly proportional to the desired FD. Under a fixed filter order, the set of normalized complex cepstra needs to be computed once and stored, and the specific set for an arbitrary FD is obtained by simply multiplying the stored set with the delay value. According to this observation, we also design two kinds of tunable filter structures consisting of several linear-phase filters, in which it is more flexible to obtain better performance by adding the extra substructure without modifying the present one. Moreover, the tunable FD is simply controlled by a single parameter, and the usage of linear-phase filters saves half of the multipliers, largely reducing the cost of hardware implementation. In addition, we obtain an IIR all-pass filter with a wider useful band than that based on Thiran's design.     

Current-Mode Filters Using Voltage Amplifiers

The case of implementation of current-mode filters is revisited using the concepts of transposed networks, and nullator-norator representation for active devices. Employing these principles, it is shown that a voltage-mode filter implemented using an ideal operational amplifier (OA) can be very easily converted to a current-mode filter using the same OA, when the OA is configured as a three-terminal inverting amplifier. In this article, we present the theoretical basis of our work and illustrate the technique using simulation and lab-bench filter models. The current-mode filters have the same frequency response and sensitivity properties as the associated voltage-mode filters.     

Design of Smearing Filters for Data Transmission Systems

In this paper, we introduce a new approach to design smearing and desmearing filters for data transmission systems to suppress pulse-like disturbances inserted in the communication channel. Our method is based on time domain considerations. It consists of the optimization of two merit factors defined for the impulse response functions of the filters. The first one is a measure of the smearing efficiency, and the second one is a measure of the amount of intersymbol interference caused by the insertion of the two filters in the transmission system. Our method will be applied to smearing and desmearing filters for baseband signals as well as for passband signals. In particular, we show that our method leads to filters having a better smearing efficiency and a simpler implementation than the filters obtained by the classical frequency domain approach.     

Single Filter Frequency Masking High-Speed Recursive Digital Filters

For recursive filter the maximal sample frequency is bounded by the recursive loops in the filter. [In this paper, it is understood that recursive filters are infinite-length impulse response (IIR) filters.] In this work, a filter structure based on the use of the frequency masking approach is presented that increases the maximal sample frequency for narrowband and wideband filters by introducing more delay elements in the recursive loops. By using identical subfilters (except for the periods), the subfilters can be mapped using folding to a single pipeline/interleaved arithmetic structure yielding an area-efficient implementation. The filters are potentially suitable for low-power implementation by using power supply voltage scaling techniques. In this work, the design of the filters is discussed and estimations of the ripples are derived. Two examples show the viability of the proposed method.     

用小波变换对ECG信号进行去噪研究

小波消失矩阶数的不同,对应的小波滤波器的幅频曲线也不相同,因此选用不同的小波滤波器对信号进行滤波,去噪效果会有明显差异。本文通过数学建模研究分析小波滤波器的幅频特性,明确小波幅频特征及与小波滤波器消失矩的阶数之间的关系,为选择最优小波滤波器提供理论依据。本文提出针对ECG噪声的频率特点实现精确陷波去噪,有效的保留了信号的奇异点与特征值,减少了信号失真。实验结果表明,选择具有相对最优消失矩阶数的提升小波滤波器对ECG进行去噪处理,可以使信号能量分布更加集中,去噪效果更好。      

HashHeat: A hashing-based spatiotemporal filter for dynamic vision sensor

Neuromorphic event-based dynamic vision sensors (DVS) have much faster sampling rates and a higher dynamic range than frame-based imagers. However, they are sensitive to background activity (BA) events that are unwanted. We propose HashHeat, a hashing-based spatiotemporal BA filter for DVS. It is the first spatiotemporal filter that doesn't scale with the DVS output size and doesn't store the 32-bits timestamps. We not only give the visual denoising effect of the filter but also use two metrics for quantitatively analyzing the filter's global performance and local performance respectively, where we introduce a novel metric for evaluating global performance. The experimental results show that HashHeat achieves similar global performance as baseline filters, but increases the signal to noise ratio by about 1.5x to nearly 5x compared with other baseline filters concerning the local performance. The hardware implementation enables HashHeat to output a labeled event every 10ns and meets the real-time requirement. And it can reduce the storage cost by 128x to 256x compared with baseline filters.     

广义中值滤波理论及其性质的研究

本文以传统的中值滤波为背景，给出了一种广义中值滤波（ＧＭＦ）的定义，并在此基础上，研究了有关数学模型、性质和基本定理。其效果不仅完善了中值类非线性滤波理论，而且还展示出一些有实用价值的新结构和新应用。     

Coherently Controlled Multifunctional Active Optical Filters

In this paper, we propose multifunctional active optical filters using coherent nonlinear effects and quantum interference in quantum-well structures. Based on the application demand, in the absence of a control laser field, these filters can be either completely opaque or transparent. However, in the presence of such a control laser, the filter structure is activated, allowing transmission of a single frequency. We show that the amplitude and linewidth of these filters can be optically controlled, demonstrating various functionalities and performances including attenuation, amplification, and switching processes. We also show that, with proper design of such active filters, one can tune the wavelength of the filtered signal by varying the intensity of the control field.