Initial-State Estimation of Multi-Channel Networked Discrete Event Systems

Initial-state estimation consists in determining the initial state of the system based on the observation from the system and the system structure. It is the basis for many problems in security applications, such as opacity, detectability and supervisory control. However, when it comes to cyber-physical systems (CPS) communication delays and losses are inevitable. In this letter, we study the initial-state estimation problem in a CPS that is modeled with a multi-channel networked discrete event system (NDES). In practice, the system is usually distributed over several locations, and the communication between the system and an agent (e.g., intruder, observer, supervisor) is carried out via a shared network, in which communication delays and losses may happen. In multi-channel NDESs, even when the first-in first-out rule is satisfied in each channel, the order of events received by the agent may still be shuffled due to random communication delays in each channel. To address these new challenges, we formalize the initial-state estimation problem in multi-channel NDESs and a networked initial-state estimator is proposed to generate the exact initial-state estimate.