Wireless communication tradeoffs in distributed control

We present a framework to study control systems with feedback loops closed over wireless communication links. We show the choice of communication parameters can greatly affect the performance of such systems. The trade-offs of data rate, time delay and packet loss in the communication link layer design are illustrated with a numerical example of an inverted pendulum. Packet loss is shown to significantly degrade performance, which is not surprising since the controller design does not take into account random packet losses in the feedback loop. We thus propose an analog soft-decoding communication link design that does not incur any packet losses. It is shown that, for low channel gains, the control system closed over a soft-decoding communication link performs better than the same system closed over a hard-decoding communication link with optimal selection of sample period and data rate. This suggests fundamental changes in wireless link designs may be necessary to support robust distributed control systems.