Robust Controller Including a Modified Smith Predictor for AQM Supporting TCP Flows

Abstract

Based on the fluid-flow model of TCP dynamics a new control structure relying on a modified Smith predictor is proposed for which some design procedures ensuring robust stability are presented. The simplest design solution has in view the cancellation of the plant poles in the ideal case by an appropriate PID controller constituted by the components of the modified Smith predictor. Another solution consists in the application of Coefficient Diagram Method which mainly allows the simultaneous design of the characteristic polynomial of the closed-loop system and of the controller on the basis of some sufficient stability conditions.