Redesigning an active queue management system

A robust proportional-integral-derivative (PID) controller is proposed for active queue management (AQM). A linear quadratic regulator (LQR) method is used to design the controller, named LQR-PID. LQR is a robust design technique as compared to classical gain-and-phase margin and dominant pole placement methods. The LQR-PID controller marks the packets according to queue length with a probability and notifies congestion to sources; in turn, sources adjust their send rate, thus maintaining queue length at the desired level in bottleneck routers. By maintaining queue length at the desired level, delay can be predicted and quality of service can be provided. Simulation results demonstrate the robustness and superiority of LQR-PID AQM as compared with other AQM schemes in the literature.