Wireless control networks

Abstract

Control networks are based on time-triggered wireless substrates for industrial automation control, such as the WirelessHART and Honeywell's OneWireless. Control networks have fundamental differences over their sensor network counterparts as they also include actuation and the physical dynamics. A great challenge in such systems is understanding cross-cutting interfaces between computing systems, control systems, sensor networks, and time-triggered communications.A mathematical framework is first proposed for modeling and analyzing multi-hop control networks that use time-triggered communication protocols. We propose formal models for analyzing robustness of multi-hop control networks, where data is exchanged through a multi-hop communication network subject to disruptions. Time-triggered protocols enable our approach to becompositional and hence addresses the problem of designing scalable scheduling and routing policies for multiple control loops closed on the same multi-hop control network.We then present a method to stabilize a plant using just a network of resource constrained wireless nodes. As opposed to traditional networked control schemes where the nodes simply route information to and from a centralized controller, our approach treats the wireless network itself as the controller. The key idea is that each node updates its internal state to be a linear combination of the states of the nodes in its neighborhood. We show that this causes the entire network to behave as a linear dynamical system, with sparsity constraints imposed by the network topology. We provide a synthesis procedure to program the network controller and present a scheme that can handle node failures while preserving stability. We also consider the design of an intrusion detection system (IDS), which observes the transmissions of certain nodes in the network and uses that information to recover the plant outputs (for diagnostic purposes) and identify malicious behavior by any of the wireless nodes in the network.