Intelligent transportation systems have become increasingly important for the public transportation in Shanghai. In response, ShanghaiGrid (SG) project aims to provide abundant intelligent transportation services to i...
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Intelligent transportation systems have become increasingly important for the public transportation in Shanghai. In response, ShanghaiGrid (SG) project aims to provide abundant intelligent transportation services to improve the traffic condition. A challenging service in SG is to accurately locate the positions of moving vehicles in realtime. In this paper, we present an innovative scheme, Hierarchical Exponential Region Organization (HERO), to tackle this problem. In SG, the location information of individual vehicles is actively logged in local nodes which are distributed throughout the city. For each vehicle, HERO dynamically maintains an advantageous hierarchy on the overlay network of local nodes to conservatively update the location information only in nearby nodes. By bounding the maximum number of hops the query is routed, HERO guarantees to meet the real-time constraint associated with each vehicle. A small-scale prototype system implementation and extensive simulations based on the real road network and trace data of vehicle movements from Shanghai demonstrate the efficacy of HERO.
In a distributedreal-time database system, the only way to ensure transaction atomicity is to investigate and develop a real-time atomic commit protocol. This paper presents the model of distributedreal-time transac...
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In a distributedreal-time database system, the only way to ensure transaction atomicity is to investigate and develop a real-time atomic commit protocol. This paper presents the model of distributedreal-time transaction and analyses all kinds of dependencies because of data conflicts access. Based on this model, we propose an optimistic real-time commit protocol, double space commit (2SC), which is specifically designed for the high-performance distributedreal-time transaction. 2SC allows a non-healthy transaction to lend its held data to the transactions in its commit dependency set. When the prepared transaction aborts, only the transactions in its abort dependency set are aborted while the transactions in its commit dependency set will execute as normal. The two properties of 2SC can reduce the data inaccessibility and the priority inversion that is inherent in distributedreal-time commit processing. Extensive simulation experiments have been performed to compare the performance of the 2SC with that of other protocols such as the base protocol, the permits reading of modified prepared-data for timeliness [IEEE Transactions on parallel and distributedsystems 11 (2) (2000) 160-181] and the deadline-driven conflict resolution [The Computer Journal 42 (8) (1999) 674-692]. The simulation results show that 2SC has the best performance. Furthermore, it is easy to incorporate in current concurrency control protocols. (C) 2002 Elsevier Inc. All rights reserved.
Two techniques that provide a compromise between the high time overhead in maintaining synchronous voting and the difficulty of combining results in asynchronous voting are proposed. These techniques are specifically ...
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Two techniques that provide a compromise between the high time overhead in maintaining synchronous voting and the difficulty of combining results in asynchronous voting are proposed. These techniques are specifically suited for real-time applications with a single-source/single-sink structure that need instantaneous error masking. They provide a compromise between a tightly synchronized system in which the synchronization overhead can be quite high, and an asynchronous system which lacks suitable algorithms for combining the output data. Both quorum-majority voting (QMV) and compare-majority voting (CMV) are most applicable to distributedreal-timesystems with single-source/single-sink tasks. All real-timesystems eventually have to resolve their outputs into a single action at some stage. The development of the advanced information processing system (AIPS) and other similar systems serve to emphasize the importance of these techniques. time bounds suggest that it is possible to reduce the overhead for quorum-majority voting to below that for synchronous voting. All the bounds assume that the computation phase is nonpreemptive and that there is no multitasking.
We present several efficient online and offline strategies for assigning periodic tasks to the nodes of a distributed system, such that the tasks can be feasibly scheduled by the node using some local static/dynamic p...
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The high complexity of distributed computer systems requires new methodologies and languages especially designed for the characteristics of these systems. Declarative languages have been proposed as a promising altern...
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The high complexity of distributed computer systems requires new methodologies and languages especially designed for the characteristics of these systems. Declarative languages have been proposed as a promising alternative because they provide a way of leaving aside system details. However, the behaviour of reactive systems cannot be described in pure relational or functional terms. We propose a declarative environment for distributed programming based on the concurrent logic language Parlog, which has the capability of expressing concurrence, communication and non-determinism in a very natural way. That is, the intrinsic parallel semantics of the concurrent logic languages make them appropriate for distributed programming. The proposed environment is particularly suitable for loosely coupled systems and it contains mechanisms for distributed process control, and both real-time and object-oriented design. Each of these characteristics is achieved by the integration, in the framework of the underlying concurrent logic language, of realtime and distributed processing control primitives and object-oriented constructions. From this viewpoint, an operational semantics is defined and some implementation issues are discussed.
Transaction management consists of many components, such as scheduling, concurrency control, recovery, and distributed commit, These components are designed independently and introduce varying levels of delays, For ex...
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Transaction management consists of many components, such as scheduling, concurrency control, recovery, and distributed commit, These components are designed independently and introduce varying levels of delays, For example, concurrency control based on distributed locking, requires additional efforts for deadlock detection and elimination, The possibility of a deadlock leads to unpredictable delays, and repeated restarts of transactions in distributedsystems, On the contrary, real-time transactions require a response within a time limit. In this study, an effort has been made for countering the delay problems.
Virtuoso VSP is a fully distributedreal-time operating system originally developed on the Inmos transputer. Its generic architecture is based on a small but very fast nanokernel and a portable preemptive microkernel....
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Virtuoso VSP is a fully distributedreal-time operating system originally developed on the Inmos transputer. Its generic architecture is based on a small but very fast nanokernel and a portable preemptive microkernel. It was further on ported in single and virtual single processor implementations to a wide range of processors. This paper describes the rationale for developing the distributed semantics of Virtuoso's microkernel and describes some of the implementation issues. The analysis is based on the parallel DSP implementations as these push the performance limits most for hard real-time applications. Extensions of the model towards heterogeneous embedded target systems are discussed.
In a distributedreal-time system, nonuniform task arrivals may temporarily overload some nodes while leaving some other nodes idle. As a result, some of the tasks on an overloaded node may miss their deadlines even i...
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In a distributedreal-time system, nonuniform task arrivals may temporarily overload some nodes while leaving some other nodes idle. As a result, some of the tasks on an overloaded node may miss their deadlines even if the overall system has the capacity to meet the deadlines of all tasks. In a companion paper [1], we proposed, without any modeling analysis, a decentralized, dynamic load sharing (LS) scheme as a solution to this problem. In this paper, we develop analytic queueing models to comparatively evaluate the proposed LS scheme as well as three other schemes: no LS, LS with random selection of a receiver node, and LS with perfect information. The evolution of a node's load state is modeled as a continuous-time semi-Markov process, where cumulative execution time (CET), rather than the commonly-used queue length (QL), is employed to describe the workload of a node. Not only fundamental differences among the different LS schemes are addressed in the analytic models, but also implementation overheads are taken into account Several metrics relevant to real-time performance are derived from these models: in particular, we evaluate the probability of a task missing its deadline, called the probability of dynamic failure. The proposed scheme is compared against other LS schemes using these performance metrics. The validity of analytic models is checked with simulations. Both analytic and simulation results indicate that by using judicious exchange/use of state information and Bayesian decision mechanism, the proposed scheme makes a significant improvement over other existing LS schemes in minimizing the probability of dynamic failure.
In this paper, we propose an approach for the real-time performance analysis of distributed software with reliability constraints, called Athena. The approach is based on the real-time and reliability performance anal...
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In this paper, we propose an approach for the real-time performance analysis of distributed software with reliability constraints, called Athena. The approach is based on the real-time and reliability performance analysis of distributed program. In Athena, two important factors, imperfect nodes and the links reliability, are introduced. The algorithms proposed in Athena generates sub-graphs, counts the reliability of each sub-graph, calculates the transmission time for all the transmission paths of each data file, and computes response time of each data file with reliability constraint. In this way, the real-time performance of distributed software with reliability constrains can be evaluated.
Although the wide integration of advanced metering infrastructure on distribution network facilitates the application of volt/var optimisation (VVO) in real-time circumstance, the contradiction between heavy computati...
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Although the wide integration of advanced metering infrastructure on distribution network facilitates the application of volt/var optimisation (VVO) in real-time circumstance, the contradiction between heavy computation load and low solution efficiency is still a big challenge, thus the system scales investigated in the literature are limited. In this study, the full AC real-time VVO is formulated based on particle swarm optimisation (PSO) framework and direct approach (DA) power flow method, where all components, such as distributed generator and on-load tap changer transformer, are formulated and integrated into the iterative DA process. Since both PSO and DA are suitable for parallel implementation, the graphics processing unit (GPU) is introduced for acceleration in order to achieve the possibility for real-time application. All the solution process is executed by GPU with the well-established data structure and thread organisation pattern, resulting in high efficiency by guaranteeing coalesced access within each warp. Case studies are conducted on four systems with sizes ranging from 136-bus to 1760-bus. Solution accuracy and convergence property are validated by the popular open source package Matpower. Based on the results from solution efficiency comparison between CPU sequential, CPU parallel, and GPU parallel programs, the promise of the proposed parallel implementation scheme for practical application is established.
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