Robust Congestion Control for High Speed Data Networks with Uncertain Time-Variant Delays: An LMI Control Approach

Jiankun Hu

School of CS&IT, RMIT

Date and time: 11.30am-12.30pm, Friday 6th August, 2004

Venue: 10.11.04

Chair: James Harland

Abstract:

This is a joint work with A/Prof. L. Xie, NTU, Singapore. In ATM network congestion control with explicit rate feedback, conventional control theories such as LQG design, Smith's predicator etc. have ignored the time-variant nature of the delays between a single congested node and the connected sources. It is very challenging to design a congestion control scheme that can address such a discrete time, time variant delay issue. Recently, M.L. Sichitiu et al (IEEE/ACM Trans. on Networking, vo.11, 2003) has indicated that an equilibrium in the buffer is impossible to achieve in the presence of time-variant forward path delays under this environment. We argue that this conclusion depends on the particular implementation strategy and should not be viewed as what it has been claimed. Further along this line, we have provided a set of sufficient conditions to find such a congestion control scheme. We first develop a delay-dependent condition for the stability and H-infinity performance of systems with time-variant delays in both the state and output equations in terms of an LMI (Linear Matrix Inequality). We use LMI condition as it is very efficient to find the solution using interior point theory. The analysis result is then applied to derive a H-infinity congestion control where the congestion problem is formulated as the H-infinity control of systems with time-variant input delays. Illustrative examples are provided to show excellent performance of the proposed algorithm in achieving an equilibrium in the buffer occupancy in the presence of time-variant delays including time-variant forward path delays. To the best of our knowledge, no such congestion control approach that accommodates directly the issue of the discrete-time, uncertain time-variant delays has been reported.

About the speaker:

Dr. Jiankun Hu is currently a senior lecturer in the School of Computer Science and Information Technology, RMIT University. He has been research fellow in EE Dept, Melbourne University; EE Dept, Delft University, the Nethwrlands; Alexander von Humboldt Research Fellow in Ruhr University, Germany.

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