Switched feedback control for wireless networked systems

In this chapter a switched output feedback control scheme for networked systems will be presented. The control scheme is applied on client-server architectures where the feedback control loop is closed over a general purpose wireless communication channel between the plant (server) and the controller (client). The inserted delays from the communication network in general are time-varying and degrade the system dynamic performance, while forcing it to instabilities. To deal with these changes a linear quadratic regulator (LQR)-output feedback control scheme is introduced, whose parameters are tuned accordingly to the variation of the measured round trip latency times. The weights of the LQR controllers are subsequently tuned using the theory of linear matrix inequalities (LMIs) to ensure a prescribed stability margin despite the variable latency time. The overall scheme resembles a gain scheduler controller with the latency times playing the role of scheduling parameter. The proposed control scheme is applied in experimental and simulation studies to a networked control system over different communication channels including: (a) the GPRS, (b) the IEEE 802.11b, and (c) the IEEE 802.11b over a mobile ad hoc sensor network (MANET). The underlying mechanisms that generate the time-varying latency times in each case will also be presented and analyzed prior to the control scheme development.