Robust congestion control for uncertain time-varying delay network systems

In this paper, an active queue management (AQM) controller is designed for the problem of congestion control. In TCP networks, the packet-dropping probability function is considered as a control input. Thus, a TCP/AQM controller is modeled as a time-varying delay system with a saturated input. The objective of the work described here is to design robust controller capable of achieving the desired queue size and guaranteeing asymptotic stability of the operating point. To achieve this aim, we have proposed an observer-based controller. For the particular TCP mode, applying the Lyapunov-Krasovskii function defined, the system can be stabilize with the obtained observer and the state feedback control law by using linear matrix inequality (LMI). Simulation results show that the derived control strategy is validated.