Power controlled fair access protocol for wireless networked control systems

Abstract

Distributed networked control systems through wireless sensor and actuator networks have a tremendous potential to improve the efficiency of many large scale system. Designing a communication protocol that satisfies the stability and safety of networked control systems is a challenging task, because there is not yet a clear understanding of the interaction between communication and control layers in the overall system. In this paper, the main challenges to design a communication protocol for networked control systems are first clarified. Starting from these requirements, a power controlled fair access protocol is proposed where nodes send packets to their respective receivers within a broadcast range in the context of random access networks. The protocol design is based on a constrained optimization problem where the objective function is the information coverage of individual nodes subject to the state update interval constraint. The state update interval is the time elapsed between successful state vector reports derived from the networked control systems. A simple power control algorithm determines the transmit power of each node to satisfy their broadcast transmissions. A distributed channel access algorithm coordinates the channel access probability of individual nodes to achieve max---min fairness of the state update interval of a random access network. The proposed protocol is applied for a conflict detection and resolution of an air transportation system. Furthermore, the protocol is compared with the default MAC and TSMA protocol (Chlamtac and Farago in IEEE/ACM Trans Netw 2(1):23---29, 1994) under various scenarios. Simulation results indicate that the protocol significantly improves the information coverage while reducing the state update interval. The proposed algorithm converges very fast while meeting the heterogeneous requirement of networked control systems. It also guarantees fairness among various nodes compared to the default MAC and TSMA protocol. By improving the communication performance, the proposed protocol improves the control efficiency and meets the safety criteria for air transportation systems.