A Technique for the Analysis of Repairable Redundant Systems

A new analytical technique is presented for evaluating the steady-state performance of large repairable systems which cannot be described in terms of series-parallel subsystems. The method, which is based on a novel combinatorial algorithm, is used to calculate the frequency of failures and expected failure durations at each node in networks of repairable devices. The networks may have multiple input and output nodes, but the uptimes and downtimes of the devices in the network are assumed to be exponentially distributed and independent. To demonstrate the usefulness of the technique for large-scale networks of general configuration, the solution of a sample problem using a pilot computer program is also included.     

Burn-In Programs for Repairable Systems

Burn-in programs are often used for automotive or airplane engines in order to eliminate early failures due to ineffective adjustments and similar repairable sources of failure. We assume that there are two operating states: Good and Poor. Each has its own reliability characteristic, and neither necessarily has any statistical property that improves with bum-in. The purpose of the bum-in program is to uncover the Poor engines and then to repair them to the Good state. We calculate the mean time to failure of such engines when a burn-in program is used and derive conditions under which a burn-in program is justified.     

Generalized Linear Mixed Models for Reliability Analysis of Multi-Copy Repairable Systems

The power law process (PLP) is usually applied to failure data from a single repairable system. When a system has a number of copies for analysis, the usual approach is to assume homogeneity among all system copies, and then to pool data from these copies. In the real world, however, it may be more reasonable to assume heterogeneity among the system copies. Therefore, this paper proposes a new generalized linear mixed model (GLMM), called PLP-GLMM, to analyse failure data from multi-copy repairable systems. In the PLP-GLMM, the underlying model for each system copy is assumed to be a PLP at Stage 1, and parameters vary among copies at Stage 2. The PLP-GLMM can make inferences about both the population, and each system copy when accounting for copy-to-copy variance. A modified Anderson-Darling test is adapted to the goodness-of-fit test of the PLP-GLMM. A numerical application is given to show the effectiveness of the model     

Optimum Preventive Maintenance Policies for Repairable Systems

This paper summarizes my recent work in analyzing preventive maintenance of the following kinds of repairable systems: 1-unit systems, 2-unit standby systems, and a system with unrepairable spare units. Some appropriate reliability measures of such systems are given, and optimum preventive maintenance policies which maximize or minimize these measures are derived under suitable conditions.     

Cost-Optimized Burn-In Duration for Repairable Electronic Systems

A mathematical model permits determining the duration of cost-optimized burn-in and evaluating the resultant saving for repairable electronics systems. Infant mortality failures occur according to a nonhomogeneous Poisson Process; repair actions restore the system to a bad-as-old condition. The s-expected costs associated with factory and field failures are traded-off with the costs of implementing a burn-in program. Under the constraints of the model, the optimum burn-in duration and consequent cost saving are independent of the eventual life of the system in the field. A numerical example illustrates these concepts.     

A New Statistical Channel Model for Hybrid-Diversity MIMO Systems

Based on analysis of spatial-diversity and polarization-diversity MIMO systems, a new modeling method, which utilizes the covariance matrix and the power matrix to build a general-purpose statistical MIMO channel model, is proposed. The new model is able to represent the characteristic of hybrid diversity, which integrates both spatial diversity and polarization diversity, and can be applied to MIMO systems with various diversity types. A comparison between the simulation results and measurements shows the validity of the proposed model as well as its advantage over an existing model.     

Availability of Some Repairable Computer Systems

A mathematical model is established for the availability of a modularly redundant repairable system which consists of many active units and one standby; coverage is considered. The hazard rates for an active unit and for the standby unit are different and are assumed to be constant. Repair time distributions are general. Availability for the system, mean system up-time, and mean system down-time are derived.     

State-Transition Monte Carlo for Evaluating Large, Repairable Systems

This paper presents a new Monte Carlo method to estimate unreliabilities of large, repairable systems which can be modeled by a stationary Markov transition diagram. Sequences of state transitions ending at absorbing states are generated, using random numbers. Times to transitions related to the state-sequences are not generated. Next, the probability of system failure occurring in a mission time along each state-sequence is calculated. Finally, the arithmetic mean of these probabilities estimates the system unreliability. This state transition Monte Carlo method yields better estimates in fewer trials than direct Monte Carlo methods. A cold-standby problem with non-identical units is also solved as a by-product of this paper.     

可修备件保障概率的适用模型

现行可修备件保障概率存在局限性,它仅适用于任务剖面为连续工作状态、现场修复和实时检修的场合,不能适应间断工作状态或外地检修或非实时检修的任一场合。导出了适应可修备件任何场合下的备件保障概率模型。     

Heuristic and Statistical Power Estimation Model for FPGA Based Wireless Systems

Wireless Personal Communications - As the technology is advancing day by day, the need of high performance devices is also increasing. High performance is achieved at the expense of high power...     

蜂窝系统上行小区间干扰链路统计分析

在同频复用网络中,小区间干扰已成为限制系统性能提升的关键因素之一。该文对单个干扰小区产生的上行小区间干扰链路进行统计建模,通过分析路损的矩生成函数和累积量生成函数,得出了干扰链路路损分布函数的近似表达式。进一步地,根据得出的统计模型分析系统参数设置对干扰路损分布的影响。研究发现,阴影衰落的标准差越大,上行干扰路损分布越接近高斯分布。另外,传播模型参数中的衰减指数也对路损分布有较大的影响。     

Statistical Analysis of a Mobile-to-Mobile Rician Fading Channel Model

Mobile-to-mobile communication is an important application for intelligent transport systems and mobile ad hoc networks. In these systems, both the transmitter and receiver are in motion, subjecting the signals to Rician fading and different scattering effects. In this paper, we present a double-ring with a line-of-sight (LOS) component scattering model and a sum-of-sinusoids simulation method to characterize the mobile-to-mobile Rician fading channel. The developed model can facilitate the physical-layer simulation for mobile ad hoc communication systems. We also derive the autocorrelation function, level crossing rate (LCR), and average fade duration (AFD) of the mobile-to-mobile Rician fading channel and verify the accuracy by simulations.     

A Spectral Model for RF Oscillators With Power-Law Phase Noise

In this paper, we apply correlation theory methods to obtain a model for the near-carrier oscillator power-spectral density (PSD). Based on the measurement-driven representation of phase noise as a sum of power-law processes, we evaluate closed form expressions for the relevant oscillator autocorrelation functions. These expressions form the basis of an enhanced oscillator spectral model that has a Gaussian PSD at near-carrier frequencies followed by a sequence of power-law regions. New results for the effect of white phase noise, flicker phase noise and random walk frequency modulated phase noise on the near-carrier oscillator PSD are derived. In particular, in the case of$1/f$phase noise, we show that despite its lack of stationarity it is possible to derive a closed form expression for its effect on an oscillator PSD and show that the oscillator output can be considered to be wide-sense stationary.     

水面舰船RCS统计模型分析

外场动态测量水面舰船的雷达截面(RCS)是获取其电磁散射特性的一种重要手段.由于受水面舰船航行时姿态变化及测量环境等影响,RCS的起伏是随机的,不规律的.首先分析了离散数据统计方法,针对某型民船的外场实测RCS数据建立了统计模型,并对其进行拟合分析,得到了其RCS起伏的统计分布规律.     

Reliability Analysis of Hierarchical Systems Using Statistical Moments

In many practical engineering circumstances, systems reliability analysis is complicated by the fact that the failure time distributions of the constituent subsystems cannot be accurately modeled by standard distributions. In this paper, we present a low-cost, compositional approach based on the use of the first four statistical moments to characterize the failure time distributions of the constituent components, subsystems, and top-level system. The approach is based on the use of Pearson distributions as an intermediate analytical vehicle, in terms of which the constituent failure time distributions are approximated. The analysis technique is presented for -out-of- systems with identical subsystems, series systems with different subsystems, and systems exploiting standby redundancy. The moment-in-moment-out approach allows for the analysis of systems with arbitrary hierarchy, and arbitrary (unimodal) failure time distributions, provided the subsystems are independent such that the resulting failure time can be expressed in terms of sums or order statistics. The technique consistently exhibits very good accuracy (on average, much less than 1 percent error) at very modest computing cost.     

Network Approaches to Finding the Reliability of Repairable Systems

Methods of determining the availability and failure frequency of systems of independent repairable units are discussed. The methods are based on representation of the system by a network or reliability block diagram. Conditions for such representation are given and methods of drawing the network are described. Two approaches for determining system reliability given the network and unit characteristics are reviewed and developed. One approach is based on successive reduction of the network and is particularly useful for series-parallel systems. The other approach is based on the determination of either the minimal paths or cuts and subsequent formula manipulations. Both approaches enable quite large systems to be analyzed.     

Markov Approach to Finding Failure Times of Repairable Systems

In analyzing repairable systems it is often necessary to determine such parameters as availability, mean cycle time, and mean time to first failure. These and other failure time measures are defined, and methods of calculating them using a Markov approach are developed. Although conceptually simple, these methods are often not practically feasible because of the large number of possible system states. Various special techniques such as lumping states or decomposing the system into independent subsystems are discussed. These techniques, if applicable, can simplify the analysis considerably.     

Determination of Test Intervals in Certain Repairable Standby Protective Systems

A System has associated with it a Safeguard such that whenever a failure in the Safeguard is detected, the System is shut down. The System is restarted as soon as the Safeguard is repaired. An example is a standby protective system attached to a nuclear power plant; as soon as failure is detected in the protective system the nuclear plant will be shut down until repair is completed. In order to insure that the Safeguard remains in the utmost state of readiness, the components of the Safeguard are periodically tested, and repaired if the test reveals a failure. In this paper we define a measure of readiness appropriate for the above systems and consider the problem of determining the testing frequency of the components of the Safeguard in such a way that an adequate level of readiness is maintained. As an illustration, the method is applied to a typical reactor-trip system.