Performance Improvement of Uncertain TCP-Networked Control Systems Using Robust AQM

This paper presents AQM design to improve the performance of networked control systems. An analytical model of the transmission control protocol (TCP) network is considered and a PID-type state feedback controller is developed to regulate the queue length. This leads to keeping network induced delay and its variation to be small enough to improve the overall performance of the NCSs. The model is assumed to possess structured uncertainties due to the stochastic nature of the network. By augmenting the TCP model with the plant equations، the closed loop system is transformed to a state-dependent delay differential equation (SDDDE). Applying the Lyapunov-Krasovskii method، a sufficient condition for the stability of this class of systems is obtained in terms of linear matrix inequality (LMI). PID controller parameters will be determined by solving these LMIs. Simulation results are presented and it has been shown that maximum allowable bound of time delay will increase in the proposed method.