Structural Properties and Stabilization of NCS with Medium Access Constraints

Abstract

This paper discusses the structural properties (reachability and observability) and stabilization of linear networked control system (NCS) whose sensors and actuators exchange information with a remote controller over a shared communication medium. Access to that medium is governed by a pair of periodic communication sequences, one for the controller-actuators path and another for the sensors-controller path. Medium access constraints mean that the controller cannot obtain all the measures from sensors and cannot send all the commands to the plant. The controller and plant handle communication disruptions in the following way: the last value stored in the zero-order holder of each actuator is used for command (which is the case of a DAC coupled to a network) and only the measured values sent by the actively communicating sensors are used to correct the estimation error at a given time-moment, ignoring other `old' measured values stored in the ADC. It is shown that there exist periodic communication sequences that preserve the reachability and observability of the plant, leading to a straightforward design of a stabilizing feedback controller involving particular control methods or the theory of periodic systems.