Ahmad Fakharian - Assistant Professor, Faculty of Electrical, Biomedical and Mechatronic Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran
Amir Abbasi - MSc, Faculty of Electrical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran

In this paper, a state feedback H controller is proposed in order to design an active queue management (AQM) system based on congestion control algorithm for networks supporting TCP protocols. In this approach, the available link bandwidth is modeled as a timevariant disturbance. The purpose of this paper is to design a controller which is capable of achieving the queue size and can guarantee asymptotic stability in the presence of disturbance. An important feature of the proposed approach is that the performance of system, including the disturbance rejection and stability of closed-loop system, are guaranteed for all round-trip times that are less than a known value. The controller design is formulated in the form of some linear matrix inequalities, which can be efficiently solved numerically. The simulation results demonstrate the effectiveness of the proposed methods in comparison with the conventional methods.

TCP, AQM, Time delay, H͚, LMI, Stability, Disturbance rejection