Tradeoffs and limitations in Networked Control Systems
Control and communication have been increasingly studied together in the recent past. The 'Satellite - Ground Controller' is a classic example of a remote control problem. Another closely related topic of study is control over an unreliable communication network and its applications seem to grow continuously. Networked Control Systems (NCS) is a rapidly growing research topic and examples of practical significance include multiple vehicle coordination, air-traffic control, and Micro-Electro-Mechanical Systems (MEMS). The work presented consists of two problems (1) The Remote control problem and (2) The Networked control problem. The remote control problem we address is the feedback stabilization of a linear discrete-time plant in feedback with a linear controller via unreliable communication channels. The channels are modeled as analog packet-drop (erasure) channels. Erasure channel is a good model of loss of data packets, typical in large networks like the Internet. We analyze the maximum sustainable erasure on the sensor and actuator channels given a level of erasure on the feedback (Service) channel and synthesize controllers. The networked control problem we address is a special case of spatially invariant plants interconnected through a static network. We consider a circular topology of interconnection and introduce a new notion of Bode sensitivity integral for networks of spatially invariant plants in feedback with static networks and comment on the fundamental limitations of design of such feedback networks.