CSS: Conditional State-Based Scheduling for Networked Control Systems

Modern industrial networked control systems (NCSs) tend to be complicated and have dynamic workload by holding a variety of applications via a shared network. The static network scheduling algorithms fit most NCSs due to their deterministic characteristics and timing guarantees, but they cannot handle dynamic workloads for lack of making on the-fly decisions. The conditional state-based scheduling adds the dynamism in the static scheduling algorithms by automata or more explicitly state chart like formalisms with conditional transitions. In this paper, we propose CSS scheme that applies the conditional state-based scheduling to dynamically schedule different applications in the industrial NCSs. CSS aims at the time-triggered network in the NCSs and uses time division multiple access (TDMA) method to let the applications access the network. To enhance the scalability of the NCSs, we design CSS as a decentralized scheme where each application in NCSs has a local scheduler to make its schedule decisions. Appropriate algorithms are applied to ensure the scheduling decisions made by the local schedulers are consistent and the desired system performance can be achieved. Simulation results demonstrate the effectiveness of the proposed scheme compared to the static TDMA used in real-time networks.