An adaptive recursive LMS filter

An adaptive, recursive, least mean-square-digital filter is heuristically derived that has the computational simplicity of existing transversal adaptive filters, with the additional capability of producing poles in the filter transfer function. Simulation results are presented to demonstrate its capability.     

High-speed recursive digital filter realization

Pipeline techniques have been successfully applied to speeding up processing in both general- and special-purpose digital computers. Application of these techniques to nonrecursive (FIR) filters has been suggested and is quite straightforward. Application to recursive (IIR) filters has not previously been shown. In this paper, the technique for applying pipeline techniques to recursive filters is shown and the advantages and disadvantages of the technique are discussed. Using these techniques, recursive digital filters operating at hitherto impossibly high rates can be designed.The basic research for this idea was supported by the Department of Electrical and Computer Engineering, University of California, Davis, California 95616. The basic idea is the subject of a pending patent application. Subsequent research was supported by the U.S. Naval Electronic Systems Command.On leave from the Department of Electrical and Computer Engineering, University of California, Davis, California 95616, USA.     

Wavelets and recursive filter banks

It is shown that infinite impulse response (IIR) filters lead to more general wavelets of infinite support than finite impulse response (FIR) filters. A complete constructive method that yields all orthogonal two channel filter banks, where the filters have rational transfer functions, is given, and it is shown how these can be used to generate orthonormal wavelet bases. A family of orthonormal wavelets that have a maximum number of disappearing moments is shown to be generated by the halfband Butterworth filters. When there is an odd number of zeros at π it is shown that closed forms for the filters are available without need for factorization. A still larger class of orthonormal wavelet bases having the same moment properties and containing the Daubechies and Butterworth filters as the limiting cases is presented. It is shown that it is possible to have both linear phase and orthogonality in the infinite impulse response case, and a constructive method is given. It is also shown how compactly supported bases may be orthogonalized, and bases for the spline function spaces are constructed     

New charge transfer recursive filter

A new fully integrated recursive charge transfer filter is described using the concept of passive recirculation of charges. This is a novel solution for voice channel or data filters in digital communications.     

Obtaining expert advice [filter synthesis]

Unlike other filter-synthesis design tools, EXSHOF employs knowledge-based synthesis of a high-order active filter. The package is completely menu driven and extremely user friendly. At the various stages of filter design it asks questions of the user and provides guidelines to these questions; i.e., it gives expert help in making decisions. It assumes that the user has little knowledge of computers and filters. Users have the option of using any of the five approximation functions or directly inputting the transfer function. It can design four types of different high-order filter structures and nine different biquad circuits. The detailed diagram of the designed circuit is presented to the user in a modular form using graphics. The frequency response of the circuit has been simulated using PSpice and it has been found that the response exactly matches the input specifications     

A simplified adaptive recursive filter design

The adaptive recursive filter design first proposed by White [1] is re-examined, and a modified filter configuration is proposed which drastically simplifies the gradient generating mechanism. The performance behavior of the simplified filter design is analyzed.     

A recursive digital MTI radar filter

An approach for designing a recursive digital MTI radar filter in the z plane is described. The resultant filter exhibits a sharp spectrum rolloff and an almost flat passband in the amplitude response.     

Stack algorithm for recursive deconvolution of Bernoulli-Gaussianprocesses [seismic exploration]

The deconvolution of pulse trains modeled as Bernoulli-Gaussian processes is addressed. The detector presented implements a stack Viterbi algorithm with a parametric level of suboptimality. Simulation results are satisfactory, even in the difficult case of a poor spectral content of the wavelet. The recursive and parallel structure of the method allows fast data processing on modern architectures     

Very low sensitivity recursive digital filter structures

A type of realisation of recursive digital filters is proposed here to give very low-magnitude transfer function sensitivity with respect to multiplier coefficients. Simulation results of sensitivity values for a simple 2nd-order filter are presented and compared with some of the existing realisations to show the order of improvements.     

Pipelined recursive filter with minimum order augmentation

Pipelining is an efficient way for improving the average computation speed of an arithmetic processor. However, for an M-stage pipeline, the result of a given operation is available only M clock periods after initiating the computation. In a recursive filter, the computation of y(n) cannot be initiated before the computations of y(n-1) through y(n-N) are completed. H.B. Voelcker and E.E. Hartquist (1970) and P.M.Kogge and H.S. Stone (1973) independently devised augmentation techniques for resolving the dependence problem in the computation of y(n). However, the augmentation required to ensure stability may be excessively high, resulting in a very complex numerator realization. A technique which results in a minimum order augmentation is presented. The complexity of the resulting filter design is very much lower. Various pipelining architectures are presented. It is demonstrated by an example that when compared to the prototype filter, the augmented filter has a lower coefficient sensitivity and better roundoff noise performance     

Moving-target-indicator recursive radar filter using bucket-brigade circuits

A prototype clutter-rejection filter for radar is described. It uses analogue shift registers of the bucket-brigade type, which, in common with charge-coupled devices, can combine the flexibility of digital processing with the simplicity of analogue operation. Certain imperfections in the devices are shown to be particularly important for moving-target-indicator filtering.     

Limitations in recursive wavefield continuation with spatialwavelets [seismic reflection modeling]

Some problem that have to be avoided in wavefield continuation in the space-frequency domain are instability, inaccuracy, and poor steep-dip performance. The practical design in convolutional operators for one-way wavefield continuation in the space-frequency domain places constraints on the operator length and range of useful wavenumbers. These problems are inherent in the design of anti-aliased, finite-length continuation operators and their subsequent application in a recursive manner. The author discusses two major limiting factors anti-aliasing and aperture limiting     

FSK demodulation using an adaptive recursive digital filter

A second-order adaptive recursive digital filter is used for frequency-shift keying (FSK) demodulation. Explicit formulas are derived for the noise variance in the frequency detector, and optimum transmitter carrier frequencies and detector threshold frequencies are calculated. A formula for the adaptation time is derived and the error probability is found. Computer simulations verify the derived results     

A class of modified adaptive recursive filter algorithms

A new class or adaptive infinite impulse response ( IIR) or recursive filter algorithms is obtained by incorporating a simple modification in the correction vectors of some existing algorithms. The resulting class of algorithms explores the inherent parallelism present in their coefficient update equations, and hence the possibility of faster initial convergence. Two IIR filter algorithms are considered for discussion and simulation.     

递归滤波用于目标增强的性能分析

时域递归滤波器由于其结构简单,被广泛用于序列图像中的降噪和目标增强处理。通过对递归滤波器输入、输出信号信噪改善比进行理论分析,得出迭代系数、目标持续长度等因素对于信噪改善比的影响关系;指出了递归滤波器设计过程中确定迭代系数时应注意的问题,并给出递归滤波用于目标增强时最佳迭代系数的确定方法。     

Time domain approach to recursive digital filter synthesis

The problem of the design of IIR digital filters, when the analog filter has been synthesized, resides in the approximation of a continuous system by means of a discrete one. We present a synthesis method which discretizes an Input-State-Output (I-S-O) model of the analog filter and is completely performed in the time domain. The basis of the method is the way in which the problem is stated, which points out the fundamental role played by the interpolator and allows an easy implementation.The main advantages of our method, with reference to traditional approaches, are:

• •- it allows direct working on continuous representations of the analog filter and the discretization does not require symbolic calculations as in approaches based on substitution techniques (for example bilinear transformation);
• •- it is completely numerical and is very simple from a computational point of view;
• •- it can be used for single and multiple input-output filters;
• •- it allows longer sampling periods using suitable interpolators.

An example is discussed which allows a comparison with the synthesis method based on bilinear transform and shows, also, that computing time may be saved as the sampling period may be traded off with the interpolator order.     

Tuning the smoothness of the recursive median filter

The median filter is a special case of nonlinear filters used for smoothing signals. Since the output of the median filter is always one of the input samples, it is conceivable that certain signals could pass through the median filter unaltered. These signals define the signature of a filter and are referred to as root signals. Median filters are known to possess the convergence property, meaning that by repeating median filtering a root signal will be found, starting from any input signal. By associating the nonlinear operation of median filtering with a two terms cost function, an optimization process that minimizes that function is obtained. Cost functions of the same type are associated with different recursive median filtering schemes by replacing the actual values inside the filter's window with the original signal. The convergence behavior of these filters and their smoothness are studied. By changing the positions of the replacements during filtering, a tuning effect of the smoothness is obtained. Simulation results show that the proposed filtering schemes provide improved performance over the standard recursive median filter, succeeding in preserving. small details and fine textures     

Stochastic analysis for the recursive median filter process

Vector probability measure functions (density function) for recursively median filtered signals are found when the underlying input binary sequences are either independent identically distributed (i.i.d.) or Markov chains. The results are parametric in the window size of the filter and in the probability distribution of the input sequence. Using statistical threshold decomposition, the same results are found for discrete alphabet random sequences that are either i.i.d. or Markov chains. Some examples illustrating the efficacy of the recursive median filter relative to the nonrecursive implementation are presented. In particular, the breakdown probabilities are tabulated for both recursive and nonrecursive median filters