Deterministic and Nonblocking Supervisory Control of Discrete Event Systems under Cyber Attacks
This work provides a theoretical foundation for ensuring deterministic and nonblocking behavior in cyber-attack scenarios, which is important for safety-critical systems but is incremental as it extends existing controllability and observability concepts to the attack context.
The paper addresses deterministic and nonblocking supervisory control of discrete event systems under cyber attacks, introducing CA-D-controllability and CA-D-observability as necessary and sufficient conditions for the existence of a deterministic supervisor, and proving that relative closure combined with these conditions is necessary and sufficient for a nonblocking supervisor.
We investigate deterministic and nonblocking supervisory control of discrete event systems under cyber-attacks using the ALTER (Attack Language for Transition-basEd Replacement) model. While prior works consider supervisory control that achieves either the large (upper bound) language or small (lower bound) language separately, deterministic supervisory control achieves both large language and small language at the same time to ensure that the language generated by the supervised system is unique and deterministic. We introduce two new concepts of CA-D-controllability and CA-D-observability and prove that they are necessary and sufficient for the existence of a deterministic supervisor. For nonblocking supervisory control, the objective is to ensure that the supervised system can always reach marked states under any attack scenario. We prove that relative closure, CA-D-controllability, and CA-D-observability together are necessary and sufficient for the existence of a nonblocking supervisor. We further develop methods to verify CA-D-controllability and CA-D-observability. We also illustrate our results using a robotic system example.