Prioritized contention resolution for random access networked control systems

Decentralized scheduling schemes offer low-cost, easy-to-install, and scalable resource allocation mechanisms suitable for networked control systems (NCS) with a large number of loops. However, contentions are unavoidable as collisions randomly occur in the communication link which lowers channel throughput and consequently compromises control performance. In this paper, we introduce a novel deterministic state-dependent prioritization policy to resolve the contention in a multi-loop NCS with random access medium. The proposed prioritization scheme can be realized within most of the shared medium technologies, e.g. ad-hoc and bus networks, aiming to decrease the collision probability. The priority for an individual control loop depends on the current local network-induced errors with a larger error leading to higher priority. We show stability of the described NCS under the proposed collision reduction mechanism according to stochastic Lyapunov-based techniques. It is demonstrated that the proposed state-dependent contention resolution is considerably effective in lowering the collision rate, though incapable of eliminating it due to the decentralized nature of the medium access control.