Delay-Resilient Fault Diagnosis of Networked Discrete-Event Systems Using Sequence Numbers

Communication networks are widely used in smart manufacturing systems due to their flexibility, low cost, mobility, and easy deployment, providing an efficient way to establish communication between devices in the plant. In many cases, the communication between devices may suffer from instabilities, leading to delays in communication and, consequently, the observation of events in a different order from their occurrence in the system. The use of unreliable communication, in general, leads to a degradation of data-driven systems, which can make them useless. In this paper, we address the problem of fault diagnosis of Networked Discrete Event Systems (NDES) resilient to observation delays in the communication network. We consider that each event is communicated together with its sequence number, and we show how the sequence number can be used to improve the fault diagnosis capability in the presence of observation delays, without the need to reorder the sequence of events that has occurred in the system. We also propose the implementation of a delay-resilient diagnoser that diagnoses the fault event based on the observed sequence of events together with their sequence numbers.