Temporal Uncertainties in Cyber-Physical Systems
A cyber-physical system (CPS) consists of two interacting subsystems, a distributed computer system (the C-system) and a physical system (the P-system) that is controlled by the C-system. The different models of time – dense time in the P-system and discrete time in the C-system – lead to an observation uncertainty at the interface of these two subsystems. Within the C-system, the jitter of the communication system can be the source of an inconsistent system state. This paper investigates the effects of the observations uncertainty and the jitter of the communication system on the causality and determinism of the system behavior in a CPS that contains a global notion of time. It comes to the conclusion that in general it is not possible to build a faithful model of a P-system in the C-system. Based on the gained insight some guidelines for the design of cyber-physical systems are given and a short note on the faithfulness of timeless (asynchronous) C- systems are contained in the final part of the paper.
This work was supported in part the EU Project GENESYS under project number FP 7/213322. Many discussions within the project and the research group on distributed real-time systems at the TU Vienna are warmly acknowledged.
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