A study on controller design for network-induced time delay system

In the NCS (networked control systems) whose control loops are closed through the serial communication channel, some important issues are network-induced time delay, multiple-packet transmission and data packet dropouts, which are caused by MAC (Medium Access Control) protocol and/or scheduling algorithm, packet size constraint of applied network and fault of the communication channel, respectively. Among these issues, the most important problem which should be overcome from the point of controller design in NCS is the network-induced time delay because the multiple-packet transmission and the data packet dropout problems can be solved by proper assumptions. As is well known, the network-induced time delay can be constant, time-varying, or random variable depending on protocol and/or scheduling algorithm, but it is needed to compensate any kinds of time delay by a proper controller. This paper focuses on LMI(Linear Matrix Inequality) based output feedback controller design in order to compensate network-induced time delay which is the limited time-varying delay in NCS. In our study, the effect of time-varying delay is regarded as a variable in a discrete-time model of NCS within sampling period. The effectiveness of the proposed output feedback controller is shown to be useful by example.