Construction of heuristic diffraction coefficients in the analytical solutions to the problems in which wave fields of different physical nature are scattered by polygonal flat plates with complex boundary conditions

The heuristic diffraction coefficients of the problem in which the wave field of an arbitrary physical nature is scattered by a polygonal flat plate with complex boundary conditions are determined. Diffraction coefficients are constructed with the help of the geometric optics coefficients of wave field reflection from an infinite plane surface by analogy with the known solution to the electrodynamic problem of diffraction by a perfectly conducting scatterer. It is established that the new approach makes it possible to derive simple formulas for diffraction coefficients. Their accuracy exceeds that of the formulas of the known heuristic analytical methods and tends to the accuracy of rigorous solutions. It is demonstrated that the derived results can be used in both electrodynamics and the other areas of physics, e.g., in calculations of the seismic wave diffraction.     

Properties of Diffraction Coefficients in the Problem of Diffraction by 3D Plane Polygon. II. Application of the Method of Fundamental Components in Practical Problems

Journal of Communications Technology and Electronics - Singular diffraction coefficients of the heuristic analytical solutions to the problem of diffraction of electromagnetic wave by a plane...     

Simplified Design of Constant Coefficient Multipliers

In many digital signal processing algorithms, e.g., linear transforms and digital filters, the multiplier coefficients are constant. Hence, it is possible to implement the multiplier using shifts, adders, and subtracters. In this work two approaches to realize constant coefficient multiplication with few adders and subtracters are presented. The first yields optimal results, i.e., a minimum number of adders and subtracters, but requires an exhaustive search. Compared with previous optimal approaches, redundancies in the exhaustive search cause the search time to be drastically decreased. The second is a heuristic approach based on signed-digit representation and subexpression sharing. The results for the heuristic are worse in only approximately 1% of all coefficients up to 19 bits. However, the optimal approach results in several different optimal realizations, from which it is possible to pick the best one based on other criteria. Relations between the number of adders, possible coefficients, and number of cascaded adders are presented, as well as exact equations for the number of required full and half adder cells. The results show that the number of adders and subtracters decreases on average 25% for 19-bit coefficients compared with the canonic signed-digit representation.     

Electromagnetic scattering by a two-dimensional wedge composed ofconductor and lossless dielectric

Electromagnetic scattering by two-dimensional wedges composed of perfectly conducting and lossless dielectric material is considered. Heuristic geometrical theory of diffraction type diffraction coefficients are presented and a hybrid moment-method/physical-optics technique is developed to verify the accuracy of the proposed diffraction coefficients. The purpose is to show that the heuristic approach can yield acceptably accurate results for a number of composite wedge geometries, rather than to present rigorous diffraction coefficients for the composite wedge per se. Calculated results are presented in which the results obtained by means of the two methods are compared. Very good agreement is achieved for a variety of wedge geometries     

Recompression of JPEG images by requantization

We report a novel heuristic for requantizing JPEG images. The resulting images are generally smaller and often have improved perceptual image quality over a "blind" requantization approach, that is, one that does not consider the properties of the quantization matrices. The heuristic is supported by a detailed mathematical treatment which incorporates the well-known Laplacian distribution of the AC discrete cosine transform (DCT) coefficients with an analysis of the error introduced by requantization. We note that the technique is applicable to any image compression method which employs discrete cosine transforms and quantization.     

Coupling coefficients of coupled laser cavities

We discuss certain properties of the coupling coefficients for a specific model consisting of two coupled resonant cavities separated by a lossy coupling gap. The coupling coefficients are here defined in the framework of time-dependent coupled-cavity theory-not as end-fire power coupling between traveling waves of two adjacent waveguides. In particular, we explore the validity of a heuristic formula for the coupling coefficients proposed in an earlier publication. It turns out that, in this example, the heuristic formula is directly applicable only if the coupling gap is lossless and off-resonance, but it becomes inapplicable if the lossless gap approaches resonance. The heuristic formula remains useful, but requires a correction if the coupling gap is lossy. The phase angle of the complex coupling coefficient is found to be linearly dependent on the width of the coupling gap, assuming the value 0 (to within multiples of 2π) for an off-resonant gap and the value ofpi/2for a resonant gap. It is not the purpose of this letter to explore properties of c³lasers or to specify their optimum operating conditions. Only the validity of the approximate coupling function is to be investigated.     

Coupling coefficients for coupled-cavity lasers

We derive simple, analytic formulas for the field coupling coefficients in a two-section coupled-cavity laser using a local field rate equation treatment. We show that there is a correction to the heuristic formulas based on power flow calculated by Marcuse; the correction is in agreement with numerical calculations from a coupled-mode approach.     

A uniform geometrical theory of diffraction for an imperfectly conducting half-plane

Diffraction tensors are presented in the context of the uniform geometrical theory of diffraction (UTD) for the high frequency scattering by an impedance half-plane at normal and oblique (skew) incidence. These are based on the exact Wiener-Hopf solution and were derived according to the UTD ansatz. In addition, unlike previous uniform diffraction coefficients, the ones given here reduce to the known UTD diffraction coefficients for the perfectly conducting case. The coefficients are explicit and therefore appropriate for practical applications. Several scattering patterns are also presented and compared to a previous heuristic solution.     

敏捷成像卫星快速需求筹划算法

敏捷成像卫星需求筹划主要解决如何判断敏捷卫星对地观测需求是否可执行以及何时执行的问题。首先,根据敏捷卫星对地观测的约束和特点,将敏捷卫星对地观测场景抽象成基于力学的理想弹簧系统,提出了常量机动时间和劲度系数的计算方法,实现模型关键参数的映射;然后,提出了一种启发式算法,利用理想弹簧系统的平衡状态时对应观测综合角度和最小的特点,通过计算系统的力平衡状态求解多个观测需求的整体最佳观测时间;最后,利用实际的观测需求,通过仿真对比验证了算法的有效性。仿真结果显示,所提算法提高了观测需求满足率和需求的优先级权重和,并且整体成像质量最优。     

Multi-path heuristic for redundancy allocation: the tree heuristic

A tree heuristic is presented for solving the general redundancy allocation problem in reliability optimization. The tree heuristic can obtain several local optima by branching off the main searching path when some criterions are satisfied. Then, the best local optima is selected for the final solution. The tree heuristic is a simple, efficient, iterative heuristic for any integer nonlinear programming problems with increasing constraint functions. Iterative heuristics are normally trapped in a local optimum. However, the tree heuristic can overcome local optima by branching the solution path. The experiments show that the proposed heuristic is very efficient in terms of solution quality, and computation time.     

Dynamic multi-cue tracking using particle filter

We consider the problem of decomposing audio into components that have different time frequency characteristics. For this, we model the components using different transforms and mixed norms applied on the transform domain coefficients. We formulate the problem as a search for a saddle point and derive algorithms through a primal-dual framework. We also discuss how to modify the primal-dual algorithms in order to derive a simpler heuristic scheme.     

Bayesian image reconstruction from partial image and aliasedspectral intensity data

An image reconstruction problem motivated by X-ray fiber diffraction analysis is considered. The experimental data are sums of the squares of the amplitudes of particular sets of Fourier coefficients of the electron density, and a part of the electron density is known. The image reconstruction problem is to estimate the unknown part of the electron density, the "image." A Bayesian approach is taken in which a prior model for the image is based on the fact that it consists of atoms, i.e., the unknown electron density consists of separated, sharp peaks. Currently used heuristic methods are shown to correspond to certain maximum a posteriori estimates of the Fourier coefficients. An analytical solution for the Bayesian minimum mean-square-error estimate is derived. Simulations show that the minimum mean-square-error estimate gives good results, even when there is considerable data loss, and out-performs the maximum a posteriori estimates.     

Transform picture coding

Picture coding by first dividing the picture into sub-pictures and then performing a linear transformation on each sub-picture cud quantizing and coding the resulting coefficients is introduced from a heuristic point of view. Various transformation, quantization, and coding strategies are discussed. A survey of all known applications of these techniques to monochromatic image coding is presented along with a summary of the dependence of performance on the basic system parameters and some conclusions.     

Wavelength Assignment to Minimize the Number of SONET ADMs in WDM Rings*†

Optical wavelength division multiplexing (WDM) rings are being deployed to support SONET/SDH self-healing rings. In such systems, multiple SONET/SDH self-healing rings are realized over a single physical optical ring through wavelength division multiplexing. The cost of such a system is dominated by the SONET add/drop multiplexers (ADMs). To minimize the system cost, algorithms must be developed to assign wavelengths to lightpaths in the system so that the number of ADMs required is minimized. This problem of optimal wavelength assignment to minimize the number of SONET ADMs is known to be NP-hard. Existing heuristic algorithms for this problem include the assign first heuristic, the iterative matching heuristic and the iterative merging heuristic. In this paper, we develop an integer linear programming (ILP) formulation for this problem, propose a new wavelength assignment heuristic, and evaluate the existing and the newly proposed heuristic using the ILP formulation. We conclude that the performance of the newly proposed heuristic is very close to optimal.     

Activity Measures for Fast Relative Power Estimation in Numerical Transformation for Low Power DSP Synthesis

In this paper, we propose a method for power optimization of digital signal processing (DSP) systems through reduction of circuit switching activity estimated from high levels in the synthesis hierarchy, namely at numerical and algorithmic levels. The optimization involves application of a numerical transformation called number-splitting on the system characteristic coefficients. The transformation alters the system characteristic coefficients while preserving the input/output relations. For each set of candidate coefficients, the corresponding signal flow-graph is constructed for evaluation of power consumption. First, the switching activity at all computation nodes of the graph are estimated using our novel activity transformation models, which quickly estimate the activity at the output of the adders and multipliers based on the activity at the inputs. Next, the activity at the inputs of each computation node are used to compute the average power consumption by that node, using our heuristic power estimators.The optimization framework can be applied to hardware-dedicated bit-serial, nibble-serial, as well as programmable word-parallel architectures. We focus on hardware-dedicated bit-serial systems, and show that up to 35 percent savings in power is achievable.     

Multiple Weighted Objectives Heuristic for the Redundancy Allocation Problem

A new heuristic is proposed and tested for system reliability optimization. The multiple weighted objective heuristic is based on a transformation of the problem into a multiple objective optimization problem, and then ultimately, transformation into a different single objective problem. The multiple objectives are to simultaneously maximize the reliability of each individual subsystem. This is a logical approach because system reliability is the product of the subsystem reliabilities, so if they are maximized, the system reliability will also be high. This new formulation and associated heuristic are then based on solving a sequence of linear programming problems. It is one of the very few optimization approaches that allow for linear programming algorithms and software to be used for the redundancy allocation problem when mixing of functionally equivalent components is allowed. Thus, it represents an efficient solution method that relies on readily available optimization tools. The heuristic is tested on many example problems, and compared to competing solution approaches. Overall, the heuristic performance is observed to be very good on the tested problem, and superior to the max-min heuristic regarding both efficiency, and performance.     

High-Frequency EM Characterization of Through-Wall Building Imaging

A high-frequency asymptotic technique based on the Uniform Geometric Theory of Diffraction (UTD) is employed for building interior imaging. The analysis is implemented using a ray-tracing technique to account for multiple scattering interactions in a building, along with a set of heuristic diffraction coefficients for dielectric wedges and corners. Imaging of the synthetic aperture radar data is carried out by the conventional fast Fourier transform method to transform to the downrange domain, and combined with a coherent near-zone imaging function for cross-range. Comparisons with experimental data for a scaled-down building model are given to demonstrate the suitability and efficacy of our analysis for through-wall building imaging. The UTD ray mechanisms account for the dominant scattering features observed in the image.     

Low-power coefficient segmentation algorithm for FIR filterimplementation

A new multiplication algorithm is introduced for the low-power implementation of digital filters on CMOS based digital signal processing systems. The algorithm decomposes individual coefficients into two less complex subcomponents. The decomposition, performed using a heuristic approach, divides a given coefficient such that a part is produced which can be implemented using a single shift operation, leaving another part with a reduced wordlength to be applied to the coefficient input of the hardware multiplier. This results in a significant reduction in the amount of switched capacitance and consequently power consumption. The authors describe the algorithm and present associated results, including the effects of overheads due to shift operations, showing up to 63% saving in power     

Optimal and heuristic algorithms for solving the binding problem

In this paper we present an optimal and a heuristic approach to solve the binding problem which occurs in high-level synthesis of digital systems. The optimal approach is based on an integer linear programming formulation. Given that such an approach is not practical for large problems, we then derive a heuristic from the ILP formulation which produces very good solutions in order of seconds. The heuristic is based on a network flow model and also considers floorplanning during the design process to minimize the interconnection area     

A Heuristic Algorithm for System Failure Frequency

For reliability analysis, the choice between tie-sets and cut-sets is not a matter of convenience but depends on assessment of computational effort. The system configuration alone determines the preference of the approach. The present paper offers a faster algorithm for evaluating system failure frequency using both approaches. An expression for system failure frequency between two specified nodes is derived using either tie-sets or cut-sets. The expression is in terms of failure frequency, availability, and unavailability of the system elements. A heuristic algorithm to obtain the expression can be programmed for a computer. The algorithm is illustrated through an example. The manner in which Abraham's algorithm can be used to determine system probability of failure using cut-sets is suggested. The algorithms are also useful for evaluating sensitivity coefficients.