Robust codiagnosability of discrete event systems

We consider robust decentralized diagnosis of discrete event systems, where the goal is to detect the occurrence of unobservable fault events using a set of local diagnosers that are themselves subject to failures. We introduce a formal notion of robust decentralized diagnosability, called robust codiagnosability, and study its properties. Two different tests of robust codiagnosability are presented; one uses diagnoser automata and the other uses verifier automata. We also revisit the problem of centralized diagnosability and study the problem of diagnosability under partial observation, where the set of observable events is reduced; in this regard, we introduce the notions of partial diagnosers and indeterminate hidden cycles, which are subsequently used in the study of robust codiagnosability.