Mohamed Abbas-Turki

Reducing the Reliability Over-Cost in Reconfiguration-Based Fault Tolerant Control Under Actuator Faults

This note addresses reconfiguration-based fault tolerance under actuator faults, for linear time invariant systems. Based on the concept of bottom-up extensible controls, a fault tolerance scheme that mixes the passive and active approaches is designed to recover all recoverable faults, and an algorithm is proposed to reduce the reliability overcost with respect to previous designs.

Self-adaptive distributed power control for opportunistic QOS provision in wireless communication networks

Emerging wireless communication networks are required to provide data services which tolerate large variations of link quality. Such applications allow flexible power control procedures. In this paper, we approach the distributed power control problem from an automatic control point of view. A new framework for opportunistic power control is proposed, where the target quality of service at each link is determined by a linear quadratic regulator controller according to a given self-adaptive criterion. Stability and convergence of proposed framework are analytically guaranteed, while its performance is confronted with other algorithms through computer simulations.

Closed-Loop Analysis and Control of Cavity Shear Layer Oscillations

This paper focuses on the closed-loop control of an incompressible flow past an open cavity. We propose a delayed feedback controller to suppress the self-sustained oscillations of the shear layer. The control law shows robustness to changes in flow conditions. An extension of the Eigensystem Realization Algorithm (ERA) to closed-loop identification, the so-called OCID technique, is used to extract the unstable linear dynamics of the cavity flow. The model-based analysis actually captures the modes against which the steady flow becomes unstable. The identified model is used to design an optimal controller, which shows both efficiency and robustness to stabilize the cavity flow.

A convex combination of H 2 and H ∞ filters for space-time adaptive equalization

In this work, H<inf>2</inf> and H<inf>∞</inf> optimization criteria are briefly discussed and evaluated in the context of adaptive space-time channel equalization. While the first criterion presents better mean performance, the second one is more appropriate for “worst case” situations. This suggests a combination of their characteristics. The paper proposes a convex combination of the H<inf>2</inf> and H<inf>∞</inf> filters, which leads to a novel equalizer structure that performs, in terms of mean square error, as well as or better than the best individual filter.

Closed-loop fluid flow control using a low dimensional model

This paper is devoted to the problem of defining a control strategy to minimize the drag of a bluff body in a 2-D cross-flow. A reduced model is obtained using a robust statistical reduction approach and an optimal orbit in the phase space is determined using an open-loop control strategy. This open-loop control law is inexpensive to derive as it relies on a reduced order model. Since the deviations from the optimal orbit are meant to remain small, the non-linear flow model can be linearized around the orbit at each time. To compensate for the deviations, a closed-loop control is applied. The design of a robust controller is difficult due to the large number of state space variables, conflicting specifications and parameter uncertainties. Further, the model is a time-varying process, so that Linear Time Invariant design methods cannot be directly applied.

Distributed power control for QoS-flexible services in wireless communication networks

This paper proposes a distributed power control framework for wireless communication networks that is able to provide a flexible QoS with the introduction of a dynamic target QoS into a conventional (fixed) target tracking power control algorithm. The target QoS of individual terminals is automatically updated according to a given performance criterion. The distributed power control is formulated as a Linear Quadratic Regulator (LQR) problem, where system operating points are met according to channel quality and the choice of key parameters. Effectiveness of the LQR-based power control is analyzed and the influence of such parameters on the algorithms performance is investigated with the help of computer experiments.

LMI CONSTRAINT FOR PHASE CONTROL OF BENDING MODES: APPLICATION TO THE ATTITUDE CONTROL OF A SATELLITE

Abstract When designing a controller, the conflict between various specifications can become very hard so that the feasibility of the control problem becomes an important question. One of the main dilemmas in satellite control is the conflict between the need to increase the bandwidth (in order to improve the time domain performances) and the instability brought by flexible modes (which are located more and more in low frequencies). To solve this problem the bending modes should be controlled in phase, by guaranteeing a sufficient phase margin for the controlled plant. Although there are different works giving a solution of the phase margin specification, the use of other classical criterion leads to poles-zeros compensations, resulting in a high sensibility to uncertainties. In this context, this paper presents a procedure based on convex constraints to control the phase of flexible modes together with handling other robust and performance objectives. The approach proposed in this work associates LMI formulations, the Youla parameterization and a cutting plane algorithm; it enables to decide on the feasibility of the problem and gives a corresponding controller.

Emulating Deformable Mirrors' Dynamics with the MINOA Bench

Temporal dynamics of a two-stage actuator arrangement (fast DM and tip-tilt mirrror/platform with poorly damped response) are emulated on MINOA bench. Their impact on closed-loop performance with a standard integrator controller is evaluated.

Hinfinity Filter with Adaptive Robustness Level for Space-Time Equalization

In this work, we propose the combination of mean performance and robustness in the context of adaptive space-time channel equalization. We first briefly discuss H₂ and H_∞ optimization criteria, which are respectively associated to mean performance and robustness. As an alternative to the convex combination of H₂ and H_∞ filters to join the desirable properties, we propose an adaptation scheme for the robustness level of the H_∞ filter for combining mean performance and robustness through a unique filter.