Co-design based approach to improve robustness in networked control systems

Traditional control systems consist of sensors, controllers, and actuators operating with tight periodic dependencies, and communicating over dedicated real-time channels such as CAN or FDDI. However, best effort networks such as 802.11 are being increasingly used in such systems. The unpredictable delays and losses in such networks violate the periodicity assumptions of digital control design, and the consequent fail-safe actions incur significant performance penalties. In this paper, we propose a co-design based approach to address the periodicity requirements of digital control design, and improve robustness by extending deadlines through graceful degradation to the fail-safe action. In particular, we analytically demonstrate significant deadline extensions in the control loop of a traffic control testbed based on our approach. Such deadline extensions also facilitate fault tolerance techniques such as component restarts, and system management mechanisms such as online component upgrades. We validate the results by experiments in the testbed.