Shape Of Impulse Response Research Articles

Channel Characterization of Diffusion-Based Molecular Communication With Multiple Fully-Absorbing Receivers

In this paper an analytical model is introduced to describe the impulse response of the diffusive channel between a pointwise transmitter and a given fully-absorbing (FA) receiver in a molecular communication (MC) system. The presence of neighbouring FA nanomachines in the environment is taken into account by describing them as sources of negative molecules. The channel impulse responses of all the receivers are linked in a system of integral equations. The solution of the system with two receivers is obtained analytically. For a higher number of receivers the system of integral equations is solved numerically. It is also shown that the channel impulse response shape is distorted by the presence of the neighbouring FA interferers. For instance, there is a time shift of the peak in the number of absorbed molecules compared to the case without interference, as predicted by the proposed model. The analytical derivations are validated by means of particle based simulations.

Signal modeling and impulse response shaping for semiconductor detectors

Signal modeling and impulse response shaping for semiconductor detectors

Refinement of the channel response system by considering time‐varying parameters for flood prediction

AbstractImpulse response functions derived from different types of flood wave equations (simplified shallow water equations) are continuously developed to conduct the linear channel routing (LCR), which is based on the linearized Saint Venant equation and has been widely applied to avoid any possibility of numerical instability. The impulse response function proposed by Dooge, Napiórkowski, and Strupczewski (1987) and derived from the dynamic wave equation with complete force terms has been acknowledged as a classic work to establish a good physical interpretation for the LCR model; however, the flexibility of altering the shape of impulse response still needs to be improved. Based on the concept of this work, this study intends to introduce the time‐varying parameters in the model, so the values of parameters can be adjusted according to the inflow condition, flood stage, and the cross‐sectional shape. Moreover, an integrated routing procedure is proposed to formulate the impulse response function for lateral‐flow inputs and then to connect multiple inputs from subwatersheds or alongside the main channel with the impulse response function of each channel segment to reflect the spatial variation of hydraulic characteristics among different segments. In the discussion of this article, the impulse response function is analysed to show its sensitivity to hydraulic variables with spatial and temporary variations. Flood‐event simulations of a studied watershed are also provided to verify the applicability of the proposed channel routing system.

Method for Digital Correction of Signals of Multirow Photodetectors for Detecting Small Objects

The method of digital correction of output signals of multirow infrared (IR) photodetectors (PDs) for detecting small objects is proposed. The method makes it possible to correct the shape of impulse response distorted by high-frequency filtering inside the PD and increase the signal/noise ratio. The presented method is compared with the matched filtering method. The effectiveness of the proposed method for reducing the number of defective “abnormally noisy” PD channels is shown. The source data for calculations are the images obtained as a result of PD tests in a small object detection mode.

Fast Algorithms for Acoustic Impulse Response Shaping

Impulse response shaping (IRS) is a prefiltering technique for modifying the characteristics of a linear channel to achieve desirable characteristics. Acoustic impulse response shaping is used to apply partial equalization to reduce the effects of reverberation on audio signals propagating inside a room and is thus used for listening room compensation. To be capable of responding rapidly to time varying room acoustics, a shaping algorithm must be computationally fast; this is difficult to achieve since the filters to be designed may have thousands of coefficients. This paper derives variants of the Dual Augmented Lagrangian Method, presents their application to the design of the shaping filters, and validates their efficacy through experimental studies. In addition, the formulations have been modified to design shaping filters that are robust to change in microphone positions.

Modeling of transmission characteristics in step-index polymer optical fiber using the matrix exponential method.

In this paper, we propose to calculate the impulse and frequency response of step-index polymer optical fiber in the presence of mode coupling using the matrix exponential method. The computation time in this method is independent of the fiber length and is typically 2 orders of magnitude shortened compared with the standard numerical procedures involving finite difference methods. Results obtained with our method are compared with those of known cases, where an analytical solution for the time-dependent power flow equation exists, and with a finite difference method. We also investigate the impact of mode coupling and differential modal attenuation on impulse response duration and shape.

Transformation of the Diffraction Spectrum at Gradients of the Object

Background. In modern information measuring systems for the study and processing of spatial signals of various physical nature, the Fourier Optics is widely used, which actualizes the problems associated with the formation of diffraction spectra by coherent optical systems. By transforming the spatial-frequency coordinates of the Fourier spectrum of a normally-illuminated transparency, one can obtain a solution to the problem of studying light diffraction on a transparency that has an inclination to the axis of the optical system. Objective. The aim of the paper is to establish a connection of the diffractive Fourier spectrum of the transparency, which has an inclination to the optical axis of the Fourier spectrum of a normally illuminated transparency, by means of the coordinates’ transformation in the space-frequency domain, expressed through the transparency rotation matrix elements. Methods . The technique is based on the transformation of the Fourier spectrum of a normal-illuminated transparency (which simulated both the passing wave and the reflected wave) at its arbitrary angular slopes in space and various special cases of the two-dimensional spectrum degeneracy. Results. The obtained results and substantiated practical recommendations can be used for the realization of practical problems using coherent optical spectral analyzers. Conclusions . The well-known fundamental studies of light diffraction on a transparency that has an inclination to the axis of the optical system have a solution to this problem by transforming the spatial-frequency coordinates of the Fourier spectrum of a normally illuminated transparency. This result is generalized with the help of the Van Cittert–Zernike theorem in the case of a partially coherent illumination. However, in these studies only a partial case of the flat transparency slope is considered in relation to only one of the coordinate axes, and in the practical applications two-coordinate inclinations and longitudinal shifts take place, that have not been investigated at the present time. The optical system that implements the Fourier transform of the transmittance (reflection) function of a transparency that has an inclination to the optical axis is frequency-non-invariant, since at the linear displacement of spatial frequencies at the input there is a nonlinear shift and the impulse response shape distortion due to the transparency slope, and expressed through the elements of the rotation matrix.

Efficient projection onto a low-dimensional ball

ABSTRACTProjection onto convex sets is a technique well known in optimization for its versatility and wide range of applications. This article presents an efficient projection onto a low-dimensional ball. The technique is based on analytically solving a quartic equation, and is exceptionally computationally efficient. An example application of this projection technique relates to acoustic impulse response shaping. Acoustic impulse response shaping is a pre-filtering technique to reduce reverberation of sound reproduction inside a room. If the focus is solely on the time domain, peaks and troughs in the frequency domain can occur. The projection approach presented in this article has been combined with the shaping algorithm to flatten the frequency response, thus providing control of both time domain and frequency domain characteristics.

A Statistically Robust Approach to Acoustic Impulse Response Shaping

Acoustic impulse response shaping is a prefiltering technique to reduce the perceptible effects of room reverberation. The room impulse responses to be shaped must first be measured, and these measurements can contain errors. Furthermore, room responses vary with changes in temperature and humidity and also with changes in measurement position. This letter presents a method for enhancing the robustness of the shaping procedure so that the effects of these errors and changes are minimized. The method uses a stochastic model of the channel variations to explicitly limit the probability of large deviations from the desired performance. The method is evaluated on realistic channel perturbations and the resulting shaped responses are shown to comply with the robustness specification.

On a Real-Time First-Order Difference Evaluation

Abstract A subject of this paper is a real-time evaluation of the first-order backward difference of a measured signal with noise. It is wellknown that a difference evaluation strongly increase a noise amplitude so the signal prefiltering is necessary. A very short review of practically used filters is given. To perform the pre-filtering operation one mainly apply linear filters characterized by their impulse response shape: finite impulse response (FIR) and infinite impulse response (IIR). To enhance the filtering operation one successfully apply so called adaptive filters and these described by non-linear characteristics. In this paper a simple non-linear filtering algorithm is proposed and examined in the first-order backward difference of a measured signal.

Sticky Information Versus Sticky Prices: A Horse Race Under a General Price-Setting Scheme

This paper compares sticky-price and sticky-information model under a more general staggering price-setting scheme. Different to Mankiw and Reis (2002), who show that, under the Calvo staggering assumption, two models generate very different inflation dynamics, I extend the constant-hazard function underlying the Calvo assumption to a general hazard function. I find that, without strategic complementarity in the price-setting, two models generate similar inflation dynamics. The distribution of price durations dominates the shape of impulse response in both models. Furthermore, with strategic complementarity, the hazard function continues to play an important role in forming inflation. In particular, under increasing hazard functions, the inflation response of the sticky-price model is more consistent with the SVAR evidence than the sticky-information model.

Inline delayed-shot migration in tilted elliptical-cylindrical coordinates

Riemannian wavefield extrapolation, a one-way wave-equation method for propagating seismic data on generalized coordinate systems, is extended to inline delayed-shot migration using 3D tilted elliptical-cylindrical (TEC) coordinate meshes. Compared to Cartesian geometries, TEC coordinates are more conformal to the shape of inline delayed-source impulse response, which allows the bulk of wavefield energy to propagate at angles lower to the extrapolation axis, thus improving global propagation accuracy. When inline coordinate tilt angles are well matched to the inline source ray parameters, the TEC coordinate extension affords accurate propagation of both steep-dip and turning-wave components important for successfully imaging complex geologic structure. Wavefield extrapolation in TEC coordinates is no more complicated than propagation in elliptically anisotropic media and can be handled by existing implicit finite-difference methods. Impulse response tests illustrate the phase accuracy of the method and show that the approach is free of numerical anisotropy. Migration tests from a realistic 3D wide-azimuth synthetic derived from a field Gulf of Mexico data set demonstrate the imaging advantages afforded by the technique, including the improved imaging of steeply dipping salt flanks at a reduced computational cost.

Numerical analysis of modal dispersion in graded-index plastic optical fibers

Modal dispersion properties of a fabricated plastic optical fiber are numerically calculated through a finite-element method. The modal index, group delay, impulse response, and output pulse shape are compared with those for the power-law profile plastic optical fiber; the influence of index profile deviations from the power-law profile is described. It is shown that index profile fluctuations in the actual index profile strongly affect the group delays, even though they are relatively small. On the other hand, they have little effect on the modal indices.

Temporal detection in human vision: dependence on eccentricity.

Studies of human perception of time-varying luminance often aim to estimate either temporal impulse response shapes or temporal modulation transfer functions (MTFs) of putative temporal processing mechanisms. Previously, temporal masking data have been used to estimate the properties and numbers of these temporal mechanisms in central vision for 1 cycle per degree (cpd) targets [Fredericksen and Hess (1998)]. The same methods have been used to explore how these properties change with stimulus energy [Fredericksen and Hess (1997)] and spatial frequency [Fredericksen and Hess (1999)]. We present here analyses of the properties of temporal mechanisms that detect temporal variations of luminance in peripheral vision. The results indicate that a two-filter model provides the best model for our masking data, but that no multiple filter model provides an acceptable fit across the range of parameters varied in this study. Single-filter modelling shows differences between processing mechanisms at 1 cpd in central vision and those that operate eccentrically. We find evidence that this change is because of differences in relative sensitivities of the mechanisms, and to differences in fundamental mechanism impulse responses.

Estimating multiple temporal mechanisms in human vision.

When studying human ability to perceive temporal changes in luminance it is customary to estimate either temporal impulse response shapes or temporal modulation transfer functions, the representation of the impulse response in the frequency domain. The advantages and limitations of previous methods are summarized. We then describe an approach based on use of an impulse response basis set that resolves some of those limitations. We next present psychophysical results for spatiotemporal signal detection in spatiotemporal noise, together with an economical model of performance. The model is based on accepted notions of psychophysical detection mechanisms and the filter basis set described in the first part of the paper. The best-fitting model requires only eight parameters, as opposed to the 198 parameters required to separately fit each psychometric function, and captures both qualitative and quantitative properties of the psychophysical data. Finally, the best-fitting model indicates that only two temporal filters are necessary to describe the performance of each of three subjects under the specific stimulus conditions employed here.

Fast converging and low complexity adaptive filtering using an averaged Kalman filter

Kalman filtering is applied to obtain a fast converging, low complexity adaptive filter that is of the matrix stepsize normalized least mean square (NLMS) type. By replacing certain variables with averages, the solution of an averaged diagonal Riccati equation allows optimal time varying adaptation gains to be precomputed or computed online with a small number of scalar Riccati equations. The adaptation gains are computed from prior assumptions on impulse response power and shape. This fact results in a systematic procedure for adaptation gain tuning in the time-varying matrix stepsize case. Simulations using music as input, show significant performance improvements as compared with the NLMS algorithm.

Multichannel monolithic front-end system design — 4. Front-end system stability and channel-to-channel coupling

The dependence of impulse response shape, cross-talks and self-excitation on stray integrated-circuit devices was investigated. A method is proposed to determine a cross-talk generator and cross-talk sensor in PSPICE simulation, and recommendations are worked out for the design layout of multichannel BJT-JFET ICs.

A new design method of 2-D linear-phase FIR filters with finite-precision coefficients

A novel approach to the design of 2-D linear-phase FIR filters with finite-precision wordlength is presented. The key idea of this approach is the shaping of the desired impulse response within time constraint imposed by the filter specification. This approach, named IRS (Impulse Response Shaping), minimizes the objective error function in logical steps by utilizing a property of Fourier series coefficients and a process similar to binary search operation. While searching for the global minima, IRS gradually modifies the error function in order to escape the local minima. The simulation results show that this method always yields much smaller maximum deviation than that of a rounded version of the infinite-precision coefficient filters. >

The design of digital filters for biomedical signal processing Part 2: Design techniques using the z-plane

Design methods for digital filters using z-plane techniques are developed out of the basic concepts described in part 1. The relationship between impulse response shape and side lobe generation in the frequency response is investigated by means of rectangular, triangular and cosine window filters. The limited choice of cut-off frequencies available for simple linear phase digital filters is explained. Design direct from the frequency domain is summarized. z-plane techniques for the design of high- and band-pass digital filters and the digital equivalents of analogue filters are described. s-plane to z-plane mapping by means of the Bilinear transformation is compared to the direct z-transform method of filter design.

Tunnelling rays in graded-index fibres

An analysis of the role of tunnelling rays in pulse propagation in graded-index fibres is presented. Tunnelling ray attenuation is handled by using the generalized parameter technique which allows attenuation coefficients to be dispensed with and relevant families of tunnelling rays to be identified. Results are given for impulse response pulse widths and shapes. Incorporation of tunnelling ray pulse contributions into the formalism for determining optimum refractive-index profiles is presented. For most cases, tunnelling ray effects are small, but significant corrections may be necessary when measurements are made on short lengths of fibre.