| We address the problem of failure diagnosis in discrete event systems with decentralized information. We propose a coordinated decentralized architecture consisting of local sites communicating with a coordinator that is responsible for diagnosing the failures occurring in the system. We extend the notion of diagnosability, originally introduced in Sampath et al. (IEEE Trans. on Automatic Control, Sep. 1995) for centralized systems, to the proposed coordinated decentralized architecture. We specify three protocols that realize the proposed architecture; each protocol is defined by the diagnostic information generated at the local sites, the communication rules used by the local sites, and the coordinator's decision rule. We analyze the diagnostic properties of each protocol. We state and prove conditions for a language to be diagnosable under each protocol. These conditions are verifiable off-line. The on-line diagnostic process is carried out using the diagnosers introduced in Sampath et al. or a slight variation of these diagnosers. The key features of the proposed protocols are: (i) they achieve, each under a set of assumptions, the same diagnostic performance as the centralized diagnoser; and (ii) they highlight the “performance vs. complexity” tradeoff that arises in coordinated decentralized architectures.; The correctness of two of the protocols relies on some stringent global ordering assumption on message reception at the coordinator's site, the relaxation of which is analyzed. We present an algorithm that attempts the ordering of messages at the coordinator site without the use of timing information. We prove that the algorithm may degrade the diagnostic performance of a protocol. Moreover, the implementation of the algorithm requires considerable additional memory and processing power at the coordinator site.; We also study an optimization problem in sensor selection that could be applied to the area of failure diagnosis. We formulate the sensor selection problem as a Markovian decision problem and identify one instance where the optimal solution can be analytically determined. |
