An Inference Methodology for Life Tests With Complete Samples or Type-II Right Censoring

We present a methodology for gaining statistical inference during the actual conduct of a life test experiment that can reduce time on test and cost. The method relies on properties of conditional order statistic distributions to convert censored data into i.i.d. uniform variates. A secondary result presents a new test for uniformity based on the convolution of these i.i.d. uniform random variables that is higher in power than the benchmark Anderson-Darling statistic in certain cases.      

Inference Based on Type-II Hybrid Censored Data From a Weibull Distribution

A hybrid censoring scheme is a mixture of type-I and type-II censoring schemes. This article presents the statistical inferences on Weibull parameters when the data are type-II hybrid censored. The maximum likelihood estimators, and the approximate maximum likelihood estimators are developed for estimating the unknown parameters. Asymptotic distributions of the maximum likelihood estimators are used to construct approximate confidence intervals. Bayes estimates, and the corresponding highest posterior density credible intervals of the unknown parameters, are obtained using suitable priors on the unknown parameters, and by using Markov chain Monte Carlo techniques. The method of obtaining the optimum censoring scheme based on the maximum information measure is also developed. We perform Monte Carlo simulations to compare the performances of the different methods, and we analyse one data set for illustrative purposes.     

An Experimental Verification of a Simple Distributed Model of MIM Capacitors for MMIC Applications

A distributed model has been derived for MIM capacitors using a simple coupled-transmission-line approach. The model has been compared with measured S-parameter data from MIM capacitors having different aspect ratios fabricated on 4-mil GaAs substrates. The agreement is very good. The derived model will converge to the first-order capacitor model, generally given in the literature, under a few assumptions.     

Variational Bayesian Inference for a Nonlinear Forward Model

Variational Bayes (VB) has been proposed as a method to facilitate calculations of the posterior distributions for linear models, by providing a fast method for Bayesian inference by estimating the parameters of a factorized approximation to the posterior distribution. Here a VB method for nonlinear forward models with Gaussian additive noise is presented. In the case of noninformative priors the parameter estimates obtained from this VB approach are identical to those found via nonlinear least squares. However, the advantage of the VB method lies in its Bayesian formulation, which permits prior information to be included in a hierarchical structure and measures of uncertainty for all parameter estimates to be obtained via the posterior distribution. Unlike other Bayesian methods VB is only approximate in comparison with the sampling method of MCMC. However, the VB method is found to be comparable and the assumptions made about the form of the posterior distribution reasonable. Practically, the VB approach is substantially faster than MCMC as fewer calculations are required. Some of the advantages of the fully Bayesian nature of the method are demonstrated through the extension of the noise model and the inclusion of automatic relevance determination (ARD) within the VB algorithm.     

A Simple Model for the Line Parameters of a Lossy Coaxial Cable Filled With a Nondispersive Dielectric

This paper discusses a simple model for approximating the per-unit-length parameters of a lossy cable providing a smooth transition from low to high frequencies. Using Schelkunoff's classical expressions for the transmission-line parameters of a coaxial line, the simple model is postulated and used to provide approximate responses that can be compared with the rigorous solutions. This approximate model is shown to be accurate and offers an alternative to evaluating the Bessel function expressions for the line parameters     

Error Probability Distribution and Density Functions for Weibull Fading Channels With and Without Diversity Combining

In this letter, a detailed theoretical analysis of probability distribution and density functions of probability of error in a wireless system is considered. Closed form expressions for distribution and density functions of the probability of error are derived for Weibull fading channels for the cases of (i) No Diversity (ND), (ii) Selection Combining (SC) diversity, and (iii) Switch and Stay Combining (SSC) diversity. Numerical results are plotted and discussed in detail for the various cases.     

PLC-Based Novel Triplexer With a Simple Structure for Optical Transceiver Module Applications

A novel triplexer is introduced for optical communication applications in this letter. The triplexer consists of two cascaded multimode interference (MMI) couplers and can be fabricated by planar lightwave circuit technology. The concept of the extraneous self-imaging phenomenon, which is not generally mentioned in MMI theory, is applied to this triplexer to design a relatively simple and compact device. From the simulation results for wavelengths of 1310, 1490, and 1550 nm, the excess losses were determined to be 1.37, 0.63, and 0.79 dB, respectively, while the extinction ratios were 15.93, 24.28, and 18.44 dB, respectively.     

A Model for the Performance Evaluation of Packet Transmissions Using Type-II Hybrid ARQ over a Correlated Error Channel

Type-II Hybrid-ARQ (Type-II HARQ) has been shown, under certain circumstances, to increase the efficiency and reduce loss of data transmissions over a wireless channel. However, it is difficult to predict how it will perform when transmission symbol errors are correlated. We present a computationally efficient approach to the performance evaluation of packet transmissions over a wireless link employing Type-II HARQ error mitigation when the physical channel is subject to correlated transmission symbol errors. This provides a tool for static or online optimization of system parameters. We present numerical results for a wide range of channel statistics, illustrating the effect of bit error correlation, bit error rate, and block size on packet latency and loss rate.     

用于Web服务的分布式信任和声誉模型

为了提高以Web服务为基础的电子商务的安全性,提出了分布式信任和声誉模型.实施此模型只需对普通Web服务体系结构做功能扩充.通过改进信任和声誉初值的方法,使好的新注册Web服务获得机会.根据Web服务的服务情况,在不同阶段信任和声誉取值来源重点各不相同.在其他用户推荐时,考虑交易金额和时间因素,可以有效地抵御共谋团体的欺诈行为.仿真测试表明提出的信任和声誉模型能达到设计目的.     

Parameter estimation for a modified Weibull distribution, for progressively type-II censored samples

In this paper, the estimation of parameters based on a progressively Type-II censored sample from a modified Weibull distribution is studied. The likelihood equations, and the maximum likelihood estimators are derived. The estimators based on a least-squares fit of a multiple linear regression on a Weibull probability paper plot are compared with the MLE via Monte Carlo simulations. The observed Fisher information matrix, as well as the asymptotic variance-covariance matrix of the MLE are derived. Approximate confidence intervals for the parameters are constructed based on the s-normal approximation to the asymptotic distribution of MLE, and log-transformed MLE. The coverage probabilities of the individual s-normal-approximation confidence intervals for the parameters are examined numerically. Some recommendations are made from the results of a Monte Carlo simulation study, and a numerical example is presented to illustrate all of the methods of inference developed here.     

相关韦布尔分布雷达杂波模拟的VC++实现与分析

韦布尔分布是雷达杂波中一种重要的概率分布模型,文中介绍了韦布尔分布杂波模拟的思路和ZMNL法模拟的步骤,重点阐述了模拟过程中的难点及解决方法,并对模拟结果进行了分析,证明了该方法的有效性和正确性。     

传输线分布参数模型与物理模型

本文详细分析了传输线的分布参数电路模型与真实的物理电路模型之间的关联,同时对均匀传输线模型给出了明确的适用范围。如此,可以解决＂电磁场＂和＂电磁兼容＂等课程中经常令学生困惑的问题,对正确理解二端口模型的本质,提高理论素养大有裨益。     

Design and Implementation of a Robust Current-Control Scheme for a PMSM Vector Drive With a Simple Adaptive Disturbance Observer

This paper introduces a robust current-control scheme for a permanent-magnet synchronous motor (PMSM) with a simple adaptive disturbance observer. The robust controller is realized by including an adaptive element in the reference-voltage-generation stage using the feedforward control. Due to the time-varying nature and the high-bandwidth property of the uncertainties in a practical PMSM drive system, the adaptive element is simply chosen as the estimated uncertainty function, which adaptively varies with different operating conditions. Subsequently, the frequency modes of the uncertainty function are embedded in the control effort, and a robust current-control performance is yielded. Furthermore, the inclusion of the estimated uncertainty function provides an efficient solution for torque-ripple minimization in PMSM drives. This is because the frequency modes of the disturbances to be eliminated, i.e., the flux harmonics, are included in the stable closed-loop system. To provide a high-bandwidth estimate of the uncertainty function, a simple adaptation law is derived using the nominal current dynamics and the steepest descent method. To guarantee the system's convergence and to properly tune the proposed observer, a stability analysis based on a discrete-time Lyapunov function has been used. Comparative evaluation experiments are presented to demonstrate the effectiveness of the proposed control scheme under different operating conditions.     

Point and interval estimation for Gaussian distribution, based on progressively Type-II censored samples

The likelihood equations based on a progressively Type-II censored sample from a Gaussian distribution do not provide explicit solutions in any situation except the complete sample case. This paper examines numerically the bias and mean square error of the MLE, and demonstrates that the probability coverages of the pivotal quantities (for location and scale parameters) based on asymptotic s-normality are unsatisfactory, and particularly so when the effective sample size is small. Therefore, this paper suggests using unconditional simulated percentage points of these pivotal quantities for constructing s-confidence intervals. An approximation of the Gaussian hazard function is used to develop approximate estimators which are explicit and are almost as efficient as the MLE in terms of bias and mean square error; however, the probability coverages of the corresponding pivotal quantities based on asymptotic s-normality are also unsatisfactory. A wide range of sample sizes and progressive censoring schemes are used in this study.     

A Simple and Approximate Model for Nonsaturated IEEE 802.11 DCF

We propose an approximate model for a nonsaturated IEEE 802.11 DCF network that is simpler than others that have appeared in the literature. Our key simplification is that the attempt rate in the nonsaturated setting can be approximated by scaling the attempt rate of the saturated setting with an appropriate factor. Use of different scaling factors leads to variants of the model for a small buffer and an infinite buffer. We develop a general fixed-point analysis that we demonstrate can have nonunique solutions for the infinite buffer model variant under moderate traffic. Nevertheless, in an asymptotic regime that applies to light traffic, we are able to prove uniqueness of the fixed point and predict the offered load at which the maximum throughput is achieved. We verify our model using ns-2 simulation and show that our MAC access delay results are the most accurate among related work, while our collision probability and throughput results achieve comparable accuracy to (D. Malone et al., 2007), (K. Duffy et al., 2007).     

一种双嵌套区域与简单区域间的拓扑关系模型

本文通过将经典4-交集矩阵中的区域内部替换为区域外部,使其可以表示RCC5关系。在此基础上定义了4×4交集矩阵,构建了双嵌套区域与简单区域间的拓扑关系模型。给出约束条件,得到双嵌套区域与简单区域间实际存在的53种拓扑关系,给出其关系示意图及概念邻域图,在此基础上建立了拓扑关系的推理系统,给出关系复合表。应用本文所建立的拓扑关系模型,可用于对台风降水区域与指定目标地区的拓扑关系进行定性模拟,对台风及降水的预警机制具有一定的指导意义。     

A Distributed and Elastic Application Processing Model for Mobile Cloud Computing

The latest developments in mobile computing technology have increased the computing capabilities of smart mobile devices (SMDs). However, SMDs are still constrained by low bandwidth, processing potential, storage capacity, and battery lifetime. To overcome these problems, the rich resources and powerful computational cloud is tapped for enabling intensive applications on SMDs. In Mobile Cloud Computing (MCC), application processing services of computational clouds are leveraged for alleviating resource limitations in SMDs. The particular deficiency of distributed architecture and runtime partitioning of the elastic mobile application are the challenging aspects of current offloading models. To address these issues of traditional models for computational offloading in MCC, this paper proposes a novel distributed and elastic applications processing (DEAP) model for intensive applications in MCC. We present an analytical model to evaluate the proposed DEAP model, and test a prototype application in the real MCC environment to demonstrate the usefulness of DEAP model. Computational offloading using the DEAP model minimizes resources utilization on SMD in the distributed processing of intensive mobile applications. Evaluation indicates a reduction of 74.6% in the overhead of runtime application partitioning and a 66.6% reduction in the CPU utilization for the execution of the application on SMD.

     

容错计算机系统的可靠性建模和分布式仿真

对容错计算机系统的可靠性进行评估是一项重要而困难的工作。为容错计算机系统的各个组成部件建立了部件级故障模型,并以此为基础建立了整个容错计算机系统的可靠性测评模型。基于所建立模型,我们提出了分布式仿真的思想,它把系统的各个部件仿真为网络上的一个站点,并增设一台服务器来对整个系统的可靠性性能进行统计和分析。仿真结果验证了建立模型的正确性和方法的有效性。     

Single-Phase Voltage Source Inverter With a Bidirectional Buck–Boost Stage for Harmonic Injection and Distributed Generation

A transformerless single-phase inverter topology is proposed that can operate over a wide dc input voltage range and has the ability to track reference signals with fast dynamics, making it suitable for harmonic elimination and distributed generation applications. The necessary capacitor and inductor are easier to design than those for filtering the output of traditional inverters. Unlike traditional inverters, no output filter stage is required. Analysis of inverter operating mechanisms is carried out for two control schemes, which are confirmed by simulation and practical results.