Control Over a Network: Using Actuation Buffers to Reduce Transmission Frequency

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Michael Epstein, Ling Shi, Stefano Di Cairano, Richard M Murray
European Control Conference, 2007 (Submitted)

We consider a discrete time linear feedback control system with additive noise where the control signals are to be sent across a data link from the controller to the actuators. Due to network constraints it is desired to reduce the transmission frequency of the control signals. We show that by including a finite sequence of predicted control signals in each communication packet the frequency of transmission can be reduced by transmitting only when the previously sent sequence has run out. The price to pay is that the closed loop error will increase. We introduce a novel communication protocol, which we call Input Difference Transmission Scheme (IDTS), which transmits control packets when the difference between the newly computed control sequence and the predicted control sequence previously transmitted is larger than a certain thresh- old. This threshold is a design parameter and we show how the closed loop behavior varies with this threshold. Simulation results are provided to augment the theory and show how the protocol works.