Continuous-time envelope-constrained filter design via DSP approach

In envelope-constrained (EC) filter design, the effect of input noise is minimised subject to the constraint that the filter's response to a specified signal fits into a prescribed envelope. The continuous-time version of this problem has been addressed using orthonormal analogue filters. The paper addresses the EC filter-design problem using a filter comprised of an A/D converter, a digital processor, a D/A converter and an analogue interpolation filter. Numerical results are presented for a number of design examples     

Design of robust envelope-constrained filter with orthonormal bases

In the continuous-time envelope-constrained (EC) filtering problem using an orthonormal filter structure, the aim is to synthesize an orthonormal filter such that the noise enhancement is minimized while the noiseless output response of the filter with respect to a specified input signal stays within the upper and lower bounds of the envelope. The noiseless output response of the optimum filter to the prescribed input signal touches the output boundaries at some points. Consequently, any disturbance in the prescribed input signal or error in the implementation of the optimal filter will result in the output constraints being violated. In this paper, we review a semi-infinite envelope-constrained filtering problem in which the constraint robustness margin of the filter is maximized, subject to a specified allowable increase in the optimal noisy power gain. Using a smoothing technique, it is shown that the solution of the optimization problem can be obtained by solving a sequence of strictly convex optimization problems with integral cost. An efficient optimization algorithm is developed based on a combination of the golden section search method and the quasi-Newton method     

On orthonormal Muntz-Laguerre filters

When the Muntz-Szasz (1953) condition holds, the Muntz-Laguerre filters form a uniformly bounded orthonormal basis in Hardy space. This has consequences in terms of optimal pole-cancellation schemes, and it also allows for a generalization of Lerch's theorem     

Robust design of envelope-constrained filters in the presence ofinput uncertainty

The maximum robustness design of envelope-constrained filters with uncertain input (ECUI) is formulated as a minimax optimization problem in which the set of feasible filters is characterized by nonsmooth matrix inequalities. An efficient design algorithm is developed to solve this problem by use of a newly developed transformation technique. The attractive feature of this algorithm is that the ECUI filter thus designed can allow for the greatest uncertainty in the input signal while still achieving the acceptable filter performance     

Some extremal properties of Daubechies filters and other orthonormal filters

New extremal properties of Daubechies 4-tap orthonormal filters are given: they maximize a certain functional, have the largest gain in (0,π/2), and allow maximum energy compaction in [0,π/2]. These properties do not carry over to Daubechies filters of arbitrary length. They complement what is known about Daubechies filters and highlight the specific role of the 4-tap filter. Moreover, we demonstrate that these properties cannot be fulfilled by any other orthonormal lowpass filter, regardless of its length.     

A new approach to the optimization of envelope-constrained filterswith uncertain input

In envelope-constrained filtering, the filter is optimized subject to the constraint that the filter response to a given signal lies within a specified envelope or mask. In a number of signal processing applications, the envelope-constrained filtering problem is more directly relevant than least squares approximation-based approaches. The present authors develop an efficient method for solving an extended version of the envelope-constrained filtering problem in which the input pulse is not known exactly but is known to lie within a specified mask. This envelope-constrained problem with uncertain input (ECUI) has been examined elsewhere, but the algorithm proposed there for its solution has, in general, inferior convergence characteristics     

A new approach to designing varicap-tuned filters

A new approach to designing electrically tuned bandpass filters that is based on the use of U-shaped resonators with several varicaps connected to each of the resonators is proposed. This approach makes it possible to improve the characteristics of the existing filters, reduce the filter passband loss and intermodulation distortions, and obtain narrow passband widths of 2% or less. It has been found experimentally that, using the new approach, the insertion loss that is similar to the loss of the filters based on p-i-n diodes has been obtained with tunable filters based on semiconductor varicaps for the first time.     

Blind adaptation of stable discrete-time IIR filters in state-space form

Blind deconvolution consists of extracting a source sequence and impulse response of a linear system from their convolution. In the presence of system zeros close to the unit circle, which give rise to very long impulse responses, infinite-impulse-response (IIR) adaptive structures are of use, whose adaptation should be carefully designed in order to guarantee stability. In this paper, we propose a blind-type discrete-time IIR adaptive filter structure realized in state-space form that, with a suitable parameterization of its coefficients, remains stable. The theory is first developed for a two-pole filter, whose numerical behavior is investigated via numerical experiments. The proposed structure/adaptation theory is then extended to a multipole structure realized as a cascade of two-pole filters. Computer-based experiments are proposed and discussed, which aim at illustrating the behavior of the filter cascade on several cases of study. The numerical results obtained show the proposed filters remain stable during adaptation and provide satisfactory deconvolution results.     

A new SURE approach to image denoising: interscale orthonormal wavelet thresholding.

This paper introduces a new approach to orthonormal wavelet image denoising. Instead of postulating a statistical model for the wavelet coefficients, we directly parametrize the denoising process as a sum of elementary nonlinear processes with unknown weights. We then minimize an estimate of the mean square error between the clean image and the denoised one. The key point is that we have at our disposal a very accurate, statistically unbiased, MSE estimate--Stein's unbiased risk estimate--that depends on the noisy image alone, not on the clean one. Like the MSE, this estimate is quadratic in the unknown weights, and its minimization amounts to solving a linear system of equations. The existence of this a priori estimate makes it unnecessary to devise a specific statistical model for the wavelet coefficients. Instead, and contrary to the custom in the literature, these coefficients are not considered random anymore. We describe an interscale orthonormal wavelet thresholding algorithm based on this new approach and show its near-optimal performance--both regarding quality and CPU requirement--by comparing it with the results of three state-of-the-art nonredundant denoising algorithms on a large set of test images. An interesting fallout of this study is the development of a new, group-delay-based, parent-child prediction in a wavelet dyadic tree.     

Genetic approach to design of multiplierless FIR filters

The design of multiplierless FIR filters using genetic algorithms is presented. The proposed algorithm uses simple operators (reproduction, crossover, and mutation) to search through the discrete coefficient space of predefined power-of-two coefficients. This approach has proved to be highly effective and outperformed existing multiplierless FIR design techniques.<>     

Alternative approach to design of wave digital filters

The purpose of the letter is to outline an approach for designing wave digital filters that is based on a suitable interpretation of the scattering parameters of a network. The approach can be used for simulating analogue, doubly terminated, lossless ladder filters.     

Alternative approach to the design of switched-capacitor filters

An alternative switched-capacitor filter design is shown to be possible using an economic form of c.c.d. A simple example of a biquadratic digital-filter section is included to illustrate the point. This leads to comment on the relationship between switched-capacitor filters, the N-path filter and the digital filter.     

An innovations approach to discrete-time detection theory (Corresp.)

A rapidly convergent approximation to the likelihood ratio for the generic problem of detecting a stationary discrete-time stochastic process in additive white Gaussian noise is formulated. The derivation is based on the innovations approach to detection theory.     

IIR filter design via Hankel-norm optimal approximation of FIRprototype filters: a streamlined approach

An improved algorithm for Hankel-norm optimal approximation of FIR by IIR discrete-time transfer functions is given which results in a straightforward and computationally efficient implementation which is less error-prone than previous approaches     

A new approach to designing computationally efficient interpolatedFIR filters

More efficient use of multipliers in FIR filters can be achieved at the expense of a slight increase in delay by designing sparse filter structures. We have developed a new, relatively simple approach to designing sparse cascaded filters, also described in the literature as interpolated FIR filters. Our method is heuristic in nature, but gives surprisingly good results without requiring iterative design or investigation of a large number of alternative parameterizations. The design uses the efficient and widely available Remez exchange algorithm along with some routines that we have written for Matlab. Although the resulting designs are not optimal in a minimax-error sense, they have reduced RMS error, which may be attractive for some applications. We give design examples, and study the effects of coefficient quantization     

Tentative approach to the design of waveguide-below-cutoff bandpass filters

This letter deals with a theoretical approach to the waveguide-below-cutoff bandpass filter. An equivalent circuit of the elementary section of the filter is used to derive the attenuation and bandpass properties. In order to explain some discrepancies between theoretical and experimental data, a more sophisticated circuit is introduced.     

Functional approach to built-in selftest of integrated digital filters

A new functional approach to the built-in selftest of integrated digital filter is proposed. The test patterns depend on the transfer function, and are independent of the filter implementation. An example illustrates the method, and shows that the stuck-at fault coverage obtained with a simple and short term patterns is about 98%.<>     

A discrete-time approach to the modeling of carrier-sensemultiple-access on the bus topology

This work carries out an exact analysis of carrier sense multiaccess (CSMA) on the bus topology using fine-grain synchronization; that is, synchronization on the order of the distance between adjacent stations. The author models a system with a finite number of users transmitting on a bus using CSMA without collision detection. The model can accommodate any arbitrary station distribution. He evaluates the throughput of the system and shows how the station location on the bus affects the throughput achieved by the different stations. The model is also used for a slightly modified version of the CSMA protocol with collision detection     

An approach to the hardware implementation of wave digital filters

An approach to implement wave digital filter is presented. The implementation method is applicable to wave digital filters containing only 3-ports adaptors, connected with reflection-free ports. All arithmetic operations are performed in a special arithmetic unit. Main features are the fact that the arithmetic units are effectively utilized, and that only a few memories of standard type are needed.