Empty vehicles management may improve the average waiting time for vehicle delivery in the Personal Rapid Transit (PRT) network. In this study, original heuristic algorithm of empty vehicle management is presented. The algorithm is tested in several benchmark PRT structures under Feniks simulation environment. The results show that significant improvements of average waiting time may be achieved just because of the multi-parameter analysis of the present network state alone rather than by the predictive use of forecasted demand. The algorithm does not use any central database of demand and location of free vehicles. Instead, it assumes the local exchange of data between stations on their state and expected vehicles. Therefore it seems well tailored to a distributed implementation.
Distributed systems, such as the Internet of Things (IoT) and cloud computing, are becoming popular. This requires modeling that reflects the natural characteristics of such systems: the locality of independent components, the autonomy of their decisions, and asynchronous communication. Automated verification of deadlocks and distributed termination supports rapid development. Existing techniques do not reflect some features of distribution. Most formalisms are synchronous and/or use some kind of global state, both of which are unrealistic. No model supports the communication duality that allows the integration of a remote procedure call and client-server paradigm into a single, uniform model. The majority of model checkers refer to total deadlocks. Usually, they do not distinguish between communication deadlocks from resource deadlocks and deadlocks from distributed termination. Some verification mechanisms check partial deadlocks at the expense of restricting the structure of the system being verified. The paper presents an original formalism for the modeling and verification of distributed systems. The Integrated Model of Distributed Systems (IMDS) defines a distributed system as two sets: states and messages, and the relationship of the “actions” between these sets. Communication duality provides projections on servers and on traveling agents, but the uniform specification of the verified system is preserved. General temporal formulas over IMDS, independent of the structure of the verified system, allow automated verification. These formulas distinguish between deadlocks and distributed termination, and between communication deadlocks and resource deadlocks. Partial deadlocks and partial termination can be checked. The Dedan tool was developed using IMDS formalism.
Personal Rapid Transit (PRT) is a promising form of urban transport. Its operation consists in the use of small unmanned vehicles which convey the passengers among stations within a dedicated network. Various aspects of the PRT network performance are frequently evaluated using the discrete-event simulation. The paper supports the need of establishing some reference models for the simulation of PRT networks, targeted mainly towards the needs of the research on network management algorithms. Three models of such PRT network models are proposed and discussed. The presented models can play the role of benchmarks which would be very useful for comparative evaluation of heuristic control algorithms, developed by different research groups.
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