An AQM algorithm based on Variable Structure PID controller

From control theoretic perspective, the Internet is a time-varying, highly nonlinear system with large time lag. The classic, fixed parameter Active Queue Management schemes are incapable of dealing with this kind of system which makes it necessary to design adaptive algorithms. In this paper we propose a Active Queue Management scheme based on Variable Structure PID controller. Variable Structure PID is a PID-like controller with its parameters being adapted in such way that: when error is big, strengthen the effect of proportional term, weaken the effects of integral and differential terms, so as to accelerate the response speed of system; when error is small, weaken the effect of proportional term while strengthen that of integral and differential terms, so as to enhance the robustness of system and improve steady state behavior. Simulations show that Variable Structure PID achieves far better performance at the cost of only tiny increase of computational complexity.