Multiuser detection using a genetic algorithm in CDMAcommunications systems

In this study, a hybrid approach that employs a genetic algorithm (GA) and a multistage detector (MSD) for the multiuser detection problem in a code-division multiple-access communications system is proposed. Using this approach: (1) the GA is used as the first stage of the MSD to provide a good initial point for successive stages of the MSD and (2) the MSD is embedded into the GA as a “genetic operator” to improve further the fitness of the population at each generation. Such a hybridization of the GA with the MSD reduces its computational complexity by providing faster convergence. In addition, a better initial data estimate supplied by the GA improves the performance of the MSD, and the embedded MSD improves the performance of the GA. Simulation results for the synchronous and asynchronous cases are provided to show that the approach is promising     

Genetic algorithms and method of moments (GA/MOM) for the design ofintegrated antennas

This paper introduces a novel technique for efficiently combining genetic algorithms (GAs) with method of moments (MoM) for integrated antenna design and explores a two example applications of the GA/MoM approach. Integral to efficient GA/MoM integration is the use of direct Z-matrix manipulation (DMM). In DMM a “mother” structure is selected and its corresponding impedance or Z-matrix is filled only once prior to beginning the GA optimization process. The GA optimizer then optimizes the design by creating substructures of the mother structure as represented by the corresponding subsets of the original mother Z-matrix. Application of DMM with GA/MoM significantly reduces the total optimization time by eliminating multiple Z-matrix fill operations. DMM also facilitates the use of matrix partitioning and presolving to further reduce the optimization time in many practical cases. The design of a broad-band patch antenna with greater than 20% bandwidth and a dual-band patch antenna are presented as examples of the utility of GA/MoM with DMM. Measured results for the dual-band antenna are compared to numerical results. Excellent agreement between numerical and measured results is observed     

Automated evaluation of critical features in VLSI layouts based onphotolithographic simulations

In this paper, we address the problem of identifying and evaluating “critical features” in an integrated circuit (IC) layout. The “critical features” (e.g., nested elbows and open ends) are areas in the layout that are more prone to defects during photolithography. As feature sizes become smaller (sub-micron range) and as the chip area becomes larger, new process techniques (such as, using phase shifted masks for photolithography), are being used. Under these conditions, the only means to design compact circuits with good yield capabilities is to bring the design and process phases of IC manufacturing closer. This can be accomplished by integrating photolithography simulators with layout editors. However, evaluation of a large layout using a photolithography simulator is time consuming and often unnecessary. A much faster and efficient method would be to have a means of automatically identifying “critical features” in a layout and then evaluate the “critical features” using a photolithography simulator. Our technique has potential for use either to evaluate the limits of any new and nonconventional process technique in an early process definition phase or in a mask house, as a postprocessor to improve the printing capability of a given mask. This paper presents a CAD tool (an Integrated CAD Framework) which is built upon the layout editor, Magic, and the process simulator, Depict 3.0, that automatically identifies and evaluates “critical features”     

Intelligent paging strategies for third generation mobiletelecommunication systems

Location management procedures, in conjunction with the millions of users expected to subscribe to third generation mobile telecommunication systems, will generate a huge signaling load. In this paper, we propose a method which aims at the reduction of signaling overhead on the radio link produced by the paging procedure. The key idea is the application of a multiple step paging strategy which operates as follows: at the instance of a call terminating to a mobile user who roams within a certain location area, paging is initially performed in a portion of the location area (the paging area) that the so-called “paging related information” indicates. On no paging response, the mobile user is paged in the complementary portion of the location area-this phase can be completed in more than one (paging) step. Various “paging related information” elements (e.g. recent interaction information, high mobility flag, etc.) can be used and several “intelligent” paging strategies can be defined. Representative paging strategies are analyzed in terms of network performance and quality of service (paging signaling, paging delay, processing power requirements), via a simulation tool which models a realistic city area environment     

Kawaihiko and the third-quartile day [traffic management]

The Kawaihiko network, linking the New Zealand universities to the Internet, pioneered traffic measurement as a tool for network management and cost recovery. Its history and its use of the real-time traffic flow measurement architecture to measure its traffic are described. The Kawaihiko members wanted a “measured bandwidth” metric which would be a good indicator of the bandwidth required to carry each site's traffic. Kawaihiko developed such a metric-the third-quartile day-based on a daily usage profile or third-quartile profile. The 3QP and 3QD are described in detail, and illustrated with typical plots from several of the Kawaihiko sites. The Kawaihiko members found 3QD to be an effective bandwidth measure, and 3QP a useful traffic management tool     

双交换遗传算法及其在非周期天线阵方向图综合中的应用

提出了一种双交换遗传出法,它拓展了传统遗传算法的基本思想,通过引入双交换繁殖操作和参数化染色体,摆脱了传统遗传算法收敛对初始群体的依赖性,避免了传统遗传算法繁琐的编解码过程,因而,它比传统遗传算法更有效和更实用,为了说明双交换遗传算法的有效性和实用性,将双交换遗传算法应用于非周期圆形天线阵扫描方向图综合,应用表明双交换遗传算法可以成为一种通用的阵列天线辐射方向图综合工具。     

Ethos: character and ethics in technical writing

Technical writing tries to be “objective” and “audience-oriented”, but it neglects an element of persuasion known in ancient rhetoric as “ethos”. This concept translates from the Greek as “character”, but that English word does not convey the concept's richness; nor does the Latin “persona”, a term sometimes used to describe the narrative voice in technical prose. “Ethos” is the root of “ethics”, which tends to objectify values and choices, alienating them from the people making them. In this paper, I suggest that an understanding of “ethos” in all its richness can help writers of technical prose to produce work that, in relation to traditionally “objective” prose, is both more readable and more ethical     

The genetic search approach. A new learning algorithm for adaptiveIIR filtering

An “evolutionary” approach called the genetic algorithm (GA) was introduced for multimodal optimization in adaptive IIR filtering. However, the disadvantages of using such an algorithm are slow convergence and high computational complexity. Initiated by the merits and shortcomings of the gradient-based algorithms and the evolutionary algorithms, we developed a new hybrid search methodology in which the genetic-type search is embedded into gradient-descent algorithms (such as the LMS algorithm). The new algorithm has the characteristics of faster convergence, global search capability, less sensitivity to the choice of parameters, and simple implementation. The basic idea of the new algorithm is that the filter coefficients are evolved in a random manner once the filter is found to be stuck at a local minimum or to have a slow convergence rate. Only the fittest coefficient set survives and is adapted according to the gradient-descent algorithm until the next evolution. As the random perturbation will be subject to the stability constraint, the filter can always minimum in a stable manner and achieve a smaller error performance with a fast rate. The article reviews adaptive IIR filtering and discusses common learning algorithms for adaptive filtering. It then presents a new learning algorithm based on the genetic search approach and shows how it can help overcome the problems associated with gradient-based and GA algorithms     

Determination of thermal compact model via evolutionary genetic optimization method

Genetic Algorithms (GA) are adaptive search algorithms based on the theory of natural selection and survival of the fittest. In this study, GA was used to derive a thermal compact model of a micro lead frame package. The GA derived model was then used to compute the junction temperature (T/sub j/) of the package for various boundary conditions. The results obtained were checked against simulation results of a detailed thermal model and were found to be within /spl plusmn/1.5% of error. Computational time taken by the detailed finite element model required approximately 4 min whereas the GA derived model took less than 35 s to generate the T/sub j/ of the package. Further, the study shows the feasibility and potential of applying GA as a powerful tool for optimization.     

A coverage analysis tool for the effectiveness of software testing

This paper describes the software testing and analysis tool, “ATAC (Automatic Test Analysis for C)”, developed as a research instrument to measure the effectiveness of testing data. It is also a tool to facilitate the design and evaluation of test cases during software development. To demonstrate the capability and applicability of ATAC, the authors obtained 12 program versions of a critical industrial application developed in a recent university/industry N-version software project, and used ATAC to analyze and compare coverage of the testing on the program versions. Preliminary results from this investigation show that ATAC is a powerful testing tool to provide testing metrics and quality control guidance for the certification of high quality software components or systems     

Quick simulation: a review of importance sampling techniques incommunications systems

Importance sampling (IS) is a simulation technique which aims to reduce the variance (or other cost function) of a given simulation estimator. In communication systems, this usually, but not always, means attempting to reduce the variance of the bit error rate (BER) estimator. By reducing the variance, IS estimators can achieve a given precision from shorter simulation runs; hence the term “quick simulation.” The idea behind IS is that certain values of the input random variables in a simulation have more impact on the parameter being estimated than others. If these “important” values are emphasized by sampling more frequently, then the estimator variance can be reduced. Hence, the basic methodology in IS is to choose a distribution which encourages the important values. This use of a “biased” distribution will, of course, result in a biased estimator if applied directly in the simulation. However, there is a simple procedure whereby the simulation outputs are weighted to correct for the use of the biased distribution, and this ensures that the new IS estimator is unbiased. Hence, the “art” of designing quick simulations via IS is entirely dependent on the choice of biased distribution. Over the last 50 years, IS techniques have flourished, but it is only in the last decade that coherent design methods have emerged. The outcome of these developments is that at the expense of increasing technical content, modern techniques can offer substantial run-time saving for a very broad range of problems. We present a comprehensive history and survey of IS methods. In addition, we offer a guide to the strengths and weaknesses of the techniques, and hence indicate which techniques are suitable for various types of communications systems. We stress that simple approaches can still yield useful savings, and so the simulation practitioner as well as the technical researcher should consider IS as a possible simulation tool     

Extraction of SPICE-type equivalent circuits of microwavecomponents and discontinuities using the genetic algorithm optimizationtechnique

In this paper, the genetic algorithm (GA) is employed as an efficient optimization tool to derive SPICE-type equivalent circuits of microwave components, and of discontinuities in coaxial lines, from their specified S-parameters. Nodal analysis and techniques are utilized in conjunction with the GA to extract these equivalent circuits, whose component values are the parameters optimized by the GA. Numerical examples, that demonstrate the fact that GA yields excellent results for the cases studied, are included in the paper     

A hypermedia environment for global collaboration

We have developed a hypermedia environment for global collaboration by knowledge workers, which consists of two modules: InterPOD and TeamSmart. InterPOD creates a “meeting room” environment for participants to access and share multimedia information from various sources, while the TeamSmart hypermedia tool supports collaboration on document production by globally dispersed teams     

Duality relationships among “space”,“time”, and “wavelength” in all-optical networks

All-optical networks (AONs) are emerging as the next generation broadband networks for both wide-area and local-area networks. New optical devices such as wavelength routers, and wavelength division switches are currently being developed to realize these AONs. In this paper, we examine “dual” properties that exist among “space”, “time”, and “wavelength” in multiplexed signals in AONs. This observation will clarify relationships among architectural alternatives and suggest novel space-time-wavelength switching structures. It will also lead to a performance analysis of all-optical networks, by exploiting some well studied results obtained for classical circuit switched systems. A study on call blocking probabilities will be reported in a separate paper     

Toward the service-rich era [optical access networks]

In order to remain viable the common carriers to develop “optical access network” based on FTTH as soon as possible. Many problems must be overcome in moving from the “metallic” world to the “optical” world, but if carriers hesitate and fail to make this move then they will be in a hopeless situation in the 21st century. This article discusses concepts for realizing optical access networks that are competitive with other media systems and for introducing them to the telephone world, to provide various attractive services to their customers and so gain their continued support     

Balanced probe extends high-frequency measurements

The balanced coaxial probe is a valuable high frequency measurement tool that avoids the limitations of conventional probes, active and passive. Its resistive input impedance and balanced design are the keys to making clean measurements in the 1 to 500 MHz range. In fact, this probe represents an extremely effective method to accurately measure a high frequency voltage between nodes a few inches apart, as the required lead lengths for such measurements cause severe overshoots for “normal” probes with capacitive input impedances     

A fuzzy due-date bargainer for the make-to-order manufacturingsystems

For a make-to-order manufacturing system, the uncertainty and flexibility of the due dates required by customers and the production capacity owned by the manufacturer can be modeled in a fuzzy environment. A combined due-date assignment and production planning methodology for the make-to-order manufacturing systems is developed. The fuzzy approach determines the optimal due dates for the manufacturer based upon a “rough-cut” resource balance, while a customer can request earlier due dates by paying a higher price to cover the extra manufacturing cost incurred. The resulting fuzzy due-date bargainer is exercised using manufacturing resource planning (MRP-II) data from a furniture manufacturing company. Experimental results indicate its potential as a useful tool for real applications