On the period of communication policies for networked control systems, and the question of zero-order holding

We discuss stochastic, linear networked control systems (NCSs) in which only a limited number of the plant\´s sensors and actuators may communicate with the controller at any one time. We explore the problem of designing an LQG controller and an accompanying periodic communication policy, using recent results that forgo optimal communication for the sake of lowering the complexity of the joint (control-communication) problem. We show that the period of the policies in question can be shorter than previously established, and that policies designed under a simpler NCS model, in which sensors and actuators are "ignored" by the controller when they are not actively communicating, can also be effective in the more complex setting which includes zero-order holding (ZOH). Interestingly, the inclusion of a ZOH - although sometimes practical - does not always lead to better performance.