Wireless Model Based Predictive Networked Control System

Abstract

Owing to their distributed architecture, networked control systems are proven to be feasible in scenarios where a spatially distributed control system is required. Traditionally, such networked control systems operate over real-time wired networks over which sensors, controllers and actuators interact with each other. Recently, in order to achieve the utmost flexibility, scalability, ease of deployment and maintainability, wireless networks such as IEEE 802.11 LANs are being preferred over dedicated wired networks. However, basic networked control systems cannot operate over general purpose wireless networks since the stability of the system is compromised due to unbounded delays and unpredictable packet losses that are typical in the wireless medium. This work proposes a novel wireless networked control system that can achieve decent control even under unbounded delay, bursts of packet loss and ambient wireless traffic. Ambient wireless traffic is handled with modified 802.11b medium access control parameters providing the proposed system with a greater medium access priority. Packet deadlines defined at each node of the system reduce unbounded packet delay to packet loss. Performance degradation due to packet loss is kept at a minimum using the predicted plant states and control signals. The proposed system is implemented and thoroughly evaluated on a dedicated test platform under numerous scenarios. Results of the experiments show that the proposed system can work under bursts of packet loss and ambient wireless traffic levels which are intolerable for basic networked control systems while not being hindered by restraining assumptions of existing methods.