Optimum consultation for parallel distributed detection systems

Wireless Networks - An optimum consultation scheme for parallel distributed detection system is proposed. Two-way communication links are assumed between a set of local sensors and the fusion...     

Performability modelling of wireless communication systems

The high expectations of performance and availability for wireless mobile systems has presented great challenges in the modelling and design of fault tolerant wireless systems. The proper modelling methodology to study the degradation of such systems is so‐called performability modelling. In this paper, we give overview of approaches for the construction and the solution of performability models for wireless cellular networks. First, we start with the Erlang loss model, in which hierarchical and composite Markov chains are constructed to obtain loss formulas for a system with channel failures. Consequently, we develop two level hierarchical models for the wireless cellular system with handoff and channel failures. Then, for a TDMA system consisting of base repeaters and a control channel, we build a hierarchical Markov chain model for automatic protection switching (APS). Finally, we discuss stochastic reward net (SRN) models for performability analysis of wireless systems. Copyright © 2003 John Wiley & Sons, Ltd.     

Performability evaluation of multicomponent fault-tolerant systems

A combined performance and reliability (performability) measure for gracefully degradable fault-tolerant systems is introduced and a closed-form, analytic solution is provided for computing the performability of a class of unrepairable systems which can be modeled by general acyclic Markov processes. This allows the study of models which consider the degradation of more than one type of system component, e.g. processors, memories, buses. An efficient evaluation algorithm is provided, with an extensive analysis of its time and space complexity. A numerical example is provided which shows how the combined performance/reliability measure provides for a complete evaluation of the relative merits of different multiprocessor structures     

Performability of electric-power systems modeled by non-homogeneousMarkov chains

This paper treats a particular type of Markov system: time nonhomogeneous Markov system in discrete time. In order to adapt measures to this kind of system, performability measures are formulated, such as new indicators more dedicated to electrical power systems like `instantaneous mean load curtailed' and `mean energy not supplied on a time interval'. This method considers hazard-rate time variation in order to: 1) obtain more-accurate and more-instructive indicators; and 2) access new performability indicators that cannot be obtained by classical methods. An example from an Electricite De France electrical substation illustrates this     

Interconnection systems for solid-state components in hybrid integrated circuits

The factors which can influence the performance and reliability of the interconnection system for solid-state components in hybrid integrated circuits are examined. The main emphasis is on materials that have received most attention in the tantalum film and silicon technologies in the Bell System. However, other materials that are being used are discussed. The interrelation of various factors in choosing an interconnection system is discussed. These factors include the composition of the materials, the methods of depositing various metals, and the properties of the substrates. Among the properties of the materials that are considered, emphasis is laid on environmental stability. The results of environmental tests on conductors and thin-film resistors under high-humidity conditions are reported. Some results on the use of silicone rubber as an encapsulant indicate this material is effective in reducing degradative action on hybrid circuits.     

A wireless controller to enhance dynamic performance of parallel inverters in distributed generation systems

This paper presents a novel control strategy for parallel inverters of distributed generation units in an AC distribution system. The proposed control technique, based on the droop control method, uses only locally measurable feedback signals. This method is usually applied to achieve good active and reactive power sharing when communication between the inverters is difficult due to its physical location. However, the conventional voltage and frequency droop methods of achieving load sharing have a slow and oscillating transient response. Moreover, there is no possibility to modify the transient response without the loss of power sharing precision or output-voltage and frequency accuracy. In this work, a great improvement in transient response is achieved by introducing power derivative-integral terms into a conventional droop scheme. Hence, better controllability of the system is obtained and, consequently, correct transient performance can be achieved. In addition, an instantaneous current control loop is also included in the novel controller to ensure correct sharing of harmonic components when supplying nonlinear loads. Simulation and experimental results are presented to prove the validity of this approach, which shows excellent performance as opposed to the conventional one.     

Optical interconnections for parallel and distributed computing

This paper reports the application of optical interconnections to a parallel an distributed computing system in the form of a calibration-free 64-Gbps/board parallel optical interconnection sub-system mounted directly on the four-CPU processor board of a newly developed parallel-processing machine, “RWC-1”. The sub-system is composed of eight parallel optical module/single-chip link large-scale integrated circuit pairs. The subsystem successfully transmitted parallel data for a variety of link lengths (between 1 m and 1 km), and with deskewing and synchronizing functions, phase-matching calibration for link lengths is automatic. Further, a method is described for the simplified merging of optical interconnections into electronic systems     

Performability enhancement of fault-tolerant software

Model-based performability evaluation is used to assess and improve the effectiveness of fault-tolerant software. The evaluation employs a measure that combines quantifications of performance and dependability in a synergistic manner, thus capturing the interaction between these two important attributes. The specific systems evaluated are a basic realization of N-version programming (NVP) (N =3) along with variants thereof. For each system, its corresponding stochastic process model is constructed in two layers, with performance and dependability submodels residing in the lower layer. The evaluation results reveal the extent to which performance, dependability, and performability of a variant are improved relative to the basic NVP system. More generally, the investigation demonstrates that such evaluations are indeed feasible and useful with regard to enhancing software performability     

A useful resource for parallel and distributed computing

Tools and environments for parallel and distributed computing is a good collection of distributed computing articles by various authors, including the editors themselves. It covers approaches to parallel computing, the art of constructing hardware and software to let multiple processors function together. It presents a survey of the most effective tools in use and case studies of particularly successful implementations.     

Monitoring distributed systems

It is suggested that a functional model of monitoring in terms of the generation, processing, dissemination, and presentation of information can help determine the facilities needed to design and construct distributed systems. Implementation issues are also discussed, with attention given to the intrusiveness of monitoring systems and object-based implementation. It is concluded that generic monitoring services are important tools for managing distributed systems and for debugging during system development. Monitoring services may also be needed as part of the application itself, such as in process control and factory automation     

Computer networks and distributed systems

Computer Networks and Distributed Systems, along with Multiprocessor Systems, comprise the class of computer systems known as Multiple Instruction Multiple Data (MIMD). We distinguish Multi-processor Systems, which are not covered in this review, from the other members of MIMD, by the degree of autonomy of the computing elements and the means of communication between them. A system where the processors communicate by using shared memory or where there is a master-slave relationship among the processors is neither a network nor a Distributed System. This paper identifies, analyzes and classifies various aspects of distributed systems.     

Modified optical frequency domain reflectometry with high spatialresolution for components of integrated optic systems

An apparatus which allows detection of scatterers and faults as well as measurement of reflections in fiber or integrated optic devices and systems with a spatial resolution in the region of 10-100 μm is discussed. The dynamic range is sufficient to detect reflection with a reflection coefficient down to 10^-10. The system uses a modified optical frequency domain reflectometry (OFDR) technique whereby signal light and local oscillator light are coupled into the waveguide under test from opposite directions. The measurement principle requires the wavelength of the light source to be swept continuously up or down. It is shown that the experimental relationship between frequency shift and waveguide length is in fairly good agreement with the theoretical estimate. Polarization-sensitive experimental results are given for reflection factors in short, side-polished polarization-maintaining fibers     

New asymptotic results in parallel distributed detection

The performance of a parallel distributed detection system is investigated as the number of sensors tends to infinity. It is assumed that the i.i.d. sensor data are quantized locally into m-ary messages and transmitted to the fusion center for binary hypothesis testing. The boundedness of the second moment of the postquantization log-likelihood ratio is examined in relation to the asymptotic error exponent. It is found that, when that second moment is unbounded, the Neyman-Pearson error exponent can become a function of the test level, whereas the Bayes error exponent remains, as previously conjectured by J.N. Tsitsiklis, (1986), unaffected. Large deviations techniques are also used to show that in Bayes testing the equivalence of absolutely optimal and best identical-quantizer systems is not limited to error exponents, but extends to the actual Bayes error probabilities up to a multiplicative constant     

Indirect closed-loop systems identification of distributed systems

In many cases it is impossible to remove the feedback during systems identification as it will make the system unstable. This paper presents an identification method for spatially interconnected distributed systems with identical subsystems operating in closed-loop feedback control. The proposed method takes into consideration the boundary conditions. The approach provides parameters estimate with minimum bias for unstable plant models when there is additive colored noise in output data. This yields consistent parameters estimate and, compared with other techniques to identify such systems under similar situations, takes far less time. The method is illustrated for two-dimensional systems (one for time and one for space), but is equally applicable for systems having more dimensions in space. The proposed technique is for general two-dimensional systems which may be causal, semi-causal (spatially interconnected systems) or non-causal. The effectiveness of the approach is demonstrated with a simulation example.     

Behavioural models for distributed Fractal components

This paper presents a formal behavioural specification framework for specifying and verifying the correct behaviour of distributed Fractal components. The first contribution is a parameterised and hierarchical behavioural model called pNets that serves as a low-level semantic framework for expressing the behaviour of various classes of distributed languages and as a common internal format for our tools. Then, we use this model to define the generation of behavioural models for applications ranging from sequential Fractal components, to distributed objects, and finally to distributed components. Our models are able to characterise both functional and non-functional behaviours and the interaction between the two concerns. Finally, this work has resulted in the development of tools allowing the non-expert programmer to specify the behaviour of his components and (semi)automatically verify properties of his application.     

Stackable system-on-packages with integrated components

In recent years, an increasing number of mobile electronic products such as mobile communicators, combining the functions of a mobile phone and a PDA are beginning to emerge. These devices are highly miniaturized and yet provide a variety of functions at ever higher speeds. Additionally, the product cycle time is getting faster, requiring short design and production cycles at ever lower cost. These trends are posing great set of challenges for the microelectronics and packaging and assembly industry. There seem to be two approaches to solve these challenges-system-in-package (SIP) by stacking of packaged integrated circuits (ICs) or system-on-package (SOP) by stacking of packages with embedded active and passive components. The buried components in SOP require significantly less space in the Z direction, thereby allowing the formation of three-dimensional (3-D) stackable packages. In this paper, two approaches for stacking SOPs were presented, the so-called chip-in-polymer (CIP) technology and duromer molded interconnect device (MID)/WLP technology.     

Performability Evaluation of Fault-Tolerant Satellite Systems

A combined performance and reliability (performability) measure for gracefully degradable fault-tolerant satellite systems is introduced, and a closed-form analytic solution is provided in order to compute the performability for a class of unrepairable systems. An efficient algorithm for the solution of Markovian models which take into account the degradation of more than one type of system components is given. By means of an example on a commercial communication-satellite system we intend to illustrate this novel measure and compare it to more conventional ones.     

互连网络接口可靠性性能分析

本文论述了互连网络接口可靠性性能，指出了它是全面、正确评价互连网络综合性能的有效方法，文中马尔可夫故障模式和更新过程故障模式，来表达互连网络中各组成部件内和部件间的故障发生模式，并以互连网络信息分组在该故障模式下的损失，作为性能评价标准对互连网络进行可靠性分析，导出有用的公式。     

分布式系统中的安全问题

信息安全在计算机系统中,尤其在分布式系统中是至关重要的。介绍了分布式计算机系统中信息安全的保障措施,着重介绍了几种常见的信息加密、解密技术的工作原理及其实现方法。