Lawrence Jenkins

Workload redistribution for fault-tolerance in a hard real-time distributed computing system

In a hard real-time distributed computing system (HRTDCS), all the tasks are required to meet their associated deadlines; a task not meeting its deadline leads to a catastrophic failure of the system. The authors consider an HRTDCS that executes both periodic and aperiodic tasks associated with timing, precedence, and resource constraints. The fault-tolerance capability in such a system is achieved through the use of time redundancy. The problem of workload redistribution for fault tolerance in an HRTDCS is studied. A graph model to represent the system workload is developed. Three performance measures for the analysis of an HRTDCS are defined. A nonpreemptive scheduling algorithm is proposed to distribute the workload of the operational nodes of the HRTDCS in the presence of both hardware and task failures. This task allocation strategy is applied to a practical system, namely, the HRTDCS onboard a spacecraft. The performance measures obtained for a typical system workload indicate that the algorithm is quite suitable for an HRTDCS with regard to uniform workload distribution.<<ETX>>

Undersea wireless sensor network for ocean pollution prevention

The ability to effectively communicate underwater has numerous applications, such as oceanographic data collection, pollution monitoring, disaster prevention, assisted navigation, tactical surveillance applications, and exploration of natural underwater sea resources. In this paper, we have developed a completely decentralized ad-hoc wireless sensor network for the ocean pollution detection. We mainly emphasize on the deployment of sensors, protocol stack, the synchronization algorithm and the routing algorithm in order to maximize the lifetime of the network and also to improve its Quality of Service (QoS).

Monitoring the effects of on-load tap changing transformers on voltage stability

It is becoming increasingly important for power system planning and operating engineers to be capable of performing comprehensive voltage stability analyses of the systems. This need is largely due to recent trends towards operating systems under stressed conditions as a result of increasing system loads without sufficient transmission and/or generation enhancements. This paper discusses effect of the on-load tap changing transformers (OLTCs) on voltage stability and identifying critical OLTCs to avoid possibilities of voltage instability conditions. The developed approach has been tested on sample systems. Results obtained on an equivalent system of 24-node practical power system are presented.

Selection of UPFC suitable locations for system security improvement under normal and network contingencies

Electric power systems are exposed to various contingencies. Network contingencies often contribute to overloading of network branches, unsatisfactory voltages and also leading to problems of stability/voltage collapse. To maintain security of the systems, it is desirable to estimate the effect of contingencies and plan suitable measures to improve system security/stability. The paper presents an approach for selection of UPFC (unified power flow controller) suitable locations considering normal and network contingencies after evaluating the degree of severity of the contingencies. The ranking is evaluated using composite criteria based fuzzy logic for eliminating masking effects. The selection of UPFC suitable locations uses the criteria on the basis of improved system security/stability. The proposed approach for selection of UPFC suitable locations has been tested under simulated conditions on a few sample power systems and the results for a real life 36-node equivalent EHV power network are presented for illustration purposes.

Hybrid algorithms for power system unit commitment

Four hybrid algorithms has been developed for the solution of the unit commitment problem. They use simulated annealing as one of the constituent techniques, and produce lower cost schedules; two of them have less overhead than other soft computing techniques. They are also more robust to the choice of parameters. A special technique avoids the generating of infeasible schedules, and thus reduces computation time.

Response Time Analysis of Messages in Controller Area Network: A Review

This paper reviews the research work done on the response time analysis of messages in controller area network (CAN) from the time CAN specification was submitted for standardization (1990) and became a standard (1993) up to the present (2012). Such research includes the worst-case response time analysis which is deterministic and probabilistic response time analysis which is stochastic. A detailed view on both types of analyses is presented here. In addition to these analyses, there has been research on statistical analysis of controller area network message response times.

S-nets: A Petri net based model for performance evaluation of real-time scheduling algorithms

A new class of nets, called S-nets, is introduced for the performance analysis of scheduling algorithms used in real-time systems Deterministic timed Petri nets do not adequately model the scheduling of resources encountered in real-time systems, and need to be augmented with resource places and signal places, and a scheduler block, to facilitate the modeling of scheduling algorithms. The tokens are colored, and the transition firing rules are suitably modified. Further, the concept of transition folding is used, to get intuitively simple models of multiframe real-time systems. Two generic performance measures, called i?½load indexi?½ and i?½balance index,i?½ which characterize the resource utilization and the uniformity of workload distribution, respectively, are defined. The utility of S-nets for evaluating heuristic-based scheduling schemes is illustrated by considering three heuristics for real-time scheduling. S-nets are useful in tuning the hardware configuration and the underlying scheduling policy, so that the system utilization is maximized, and the workload distribution among the computing resources is balanced.

A three phase fault detection algorithm for radial distribution networks

Distribution networks, unlike in transmission system, may not be provided with protective devices or circuit breakers in each branch of the feeder. For any fault in the feeder, a large part of the feeder, may be isolated depending on the circuit breaker installation. For the purpose of speedy repair work and maintenance, it is important to find the exact fault location and type of fault. This paper presents an algorithmic approach for finding the location and type of fault based on the three phase measurements obtained for state estimation. Results of the simulated fault conditions on practical distribution systems are presented.

Properties and performance of folded cube-connected cycles

Abstract This paper analyzes a new multiprocessor interconnection network — the folded cube-connected cycles (FCCC). This topology is obtained by replacing each node of an n -dimensional folded hypercube by an ( n + 1)-cycle. The FCCC n is a regular network of degree 3 and has ( n + 1)2 n nodes. We analyze the topological properties of the FCCC and compare them with those of the cube-connected cycles (CCC). The FCCC has a lower diameter and average distance than that of the CCC. In terms of the most commonly used cost metric (node degree x diameter), the FCCC is better than any of the hypercube-variant networks. It is strongly resilient, and has a fault diameter less than that of the CCC. In terms of bisection width and connectivity also, the FCCC is better than that of the CCC. We propose algorithms for one-to-one communication and broadcasting in FCCC. We also propose an optimal VLSI layout.

Title: Challenges in deployment of wireless sensor networks

Summary form only given. Sensor networks are deployed for real-time monitoring of large objects and systems such as volcanoes, bird nesting habitats, chemical plants, bridges and civil structures. A network consists of a large number of sensor nodes, each of which consists of a CPU with memory, a battery, one or more sensors and a radio trans-receiver. The nodes are deployed randomly over the terrain associated with the application. The topology of the network is irregular, and the nodes communicate with the base station through multi-hop paths. In many cases, the environment is hostile, so node failure is significant, occasionally a node is temporarily unavailable, and communication incurs significant packet loss. Once the energy of a node is depleted, it can no longer contribute to the operation of the sensor network; after a significant number of nodes fail, the life of the network is over. All aspects of sensor network design have to take into account the unreliability and unavailability of nodes, the limited available energy at each node, the irregular nature of the network and the packet losses during communication. In this presentation, we will look at some aspects of sensor network topology, communication mechanisms, task allocation, mode localization and other interesting problems. All algorithms that we look at are decentralized, since frequent node failures would make any centralized algorithm unviable. The algorithms also need to be robust, and to take into account the redundancy in the network. Message latency is not a major consideration in most cases, and response times are not critical. The most important consideration is energy usage, since the network life-time is critically dependent on how rapidly the battery power is depleted. The purpose of the talk is to provide an overview of the principles and challenges of wireless network implementation, rather that attempting to provide a specialized state-of-the-art presentation of one or two topics of relevance.