121 research outputs found
Design and performance evaluation of a state-space based AQM
Recent research has shown the link between congestion control in
communication networks and feedback control system. In this paper, the design
of an active queue management (AQM) which can be viewed as a controller, is
considered. Based on a state space representation of a linearized fluid flow
model of TCP, the AQM design is converted to a state feedback synthesis problem
for time delay systems. Finally, an example extracted from the literature and
simulations via a network simulator NS (under cross traffic conditions) support
our study
Robust control tools for traffic monitoring in TCP/AQM networks
Several studies have considered control theory tools for traffic control in
communication networks, as for example the congestion control issue in IP
(Internet Protocol) routers. In this paper, we propose to design a linear
observer for time-delay systems to address the traffic monitoring issue in
TCP/AQM (Transmission Control Protocol/Active Queue Management) networks. Due
to several propagation delays and the queueing delay, the set TCP/AQM is
modeled as a multiple delayed system of a particular form. Hence, appropriate
robust control tools as quadratic separation are adopted to construct a delay
dependent observer for TCP flows estimation. Note that, the developed mechanism
enables also the anomaly detection issue for a class of DoS (Denial of Service)
attacks. At last, simulations via the network simulator NS-2 and an emulation
experiment validate the proposed methodology
On the necessity of sufficient LMI conditions for time-delay systems arising from Legendre approximation
This work is dedicated to the stability analysis of time-delay systems with a single constant delay using the Lyapunov-Krasovskii
theorem. This approach has been widely used in the literature and numerous sufficient conditions of stability have been proposed
and expressed as linear matrix inequalities (LMI). The main criticism of the method that is often pointed out is that these LMI
conditions are only sufficient, and there is a lack of information regarding the reduction of the conservatism. Recently, scalable
methods have been investigated using Bessel-Legendre inequality or orthogonal polynomial-based inequalities. The interest
of these methods relies on their hierarchical structure with a guarantee of reduction of the level of conservatism. However,
the convergence is still an open question that will be answered for the first time in this paper. The objective is to prove that
the stability of a time-delay system implies the feasibility of these scalable LMI, at a sufficiently large order of the Legendre
polynomials. Moreover, the proposed contribution is even able to provide an analytic estimation of this order, giving rise to a
necessary and sufficient LMI for the stability of time-delay systems
On Designing Lyapunov-Krasovskii Based AQM for Routers Supporting TCP Flows
For the last few years, we assist to a growing interest of designing AQM
(Active Queue Management) using control theory. In this paper, we focus on the
synthesis of an AQM based on the Lyapunov theory for time delay systems. With
the help of a recently developed Lyapunov-Krasovskii functional and using a
state space representation of a linearized fluid model of TCP, two robust AQMs
stabilizing the TCP model are constructed. Notice that our results are
constructive and the synthesis problem is reduced to a convex optimization
scheme expressed in terms of linear matrix inequalities (LMIs). Finally, an
example extracted from the literature and simulations via {\it NS simulator}
support our study
Multiple time-delays system modeling and control for router management
Abstract-This paper investigates the overload problem of a single congested router in TCP (Transmission Control Protocol) networks. To cope with the congestion phenomenon, we design a feedback control based on a multiple time-delays model of the set TCP/AQM (Active Queue Management). Indeed, using robust control tools, especially in the quadratic separation framework, the TCP/AQM model is rewritten as an interconnected system and a structured state feedback is constructed to stabilize the network variables. Finally, we illustrate the proposed methodology with a numerical example and simulations using NS-2 [1] simulator
Sliding mode control of systems with time-varying delays via descriptor approach
International audienceIn this paper, we combine a descriptor approach to stability and control of linear systems with time-varying delays, which is based on the Lyapunov-Krasovskii techniques, with a recent result on sliding mode control of such systems. The systems under consideration have norm-bounded uncertainties and uncertain bounded delays. The solution is given in terms of linear matrix inequalities (LMIs) and improves the previous results based on other Lyapunov techniques. A numerical example illustrates the advantages of the new method
Stability and stabilization of distributed time delay systems
International audienceThis paper is dedicated to the stability and stabilization of state-distributed delay systems. The key idea is to express the distributed delay system as a barycentric sum of linear pointwise time delay systems. By using this reformulation, new stability criterion is proposed and is formulated in the form of Linear Matrix Inequality. These conditions for the stability of the system are obtained by using a Lyapunov Krasovskii functional . Based on this stability criterion, new types of controllers, taking into account the delayed part, are designed to ensure the asymptotic stability of the system. Several examples illustrate the proposed method
Input-output framework for robust stability of time-varying delay systems
International audienceThe paper is devoted to the stability analysis of linear time varying delay. We first model the time varying delay system as an interconnected system between a known linear transformation and some operators depending explicitly on the delay. Embedding operators related to the delay into an uncertain set, stability of such system is then performed by adopting the quadratic separation approach. Having recognized that the conservatism comes from the choice of the feedback modeling and the operators definition, these first results are afterwards enhanced by using some redundant equation and scaling filter. At last, numerical examples are given to illustrate the results
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