All Years Seminars
[INMA] 2014-02-25 (14.00) : Stabilization of Distributed Parameter Systems by State Feedback with Positivity Constraints
At Euler building
Speaker :
Joseph Winkin ( FUNDP )
Abstract :
Positive linear systems are linear dynamical systems whose state trajectories are nonnegative for every nonnegative initial state and for all nonnegative input functions. Positive systems are of great importance, as the nonnegativity property occurs quite frequently in practical applications where the state variables correspond to quantities that do not have real meaning unless they are nonnegative, like the concentrations of species involved in chemical reactions. The positivity property for infinite-dimensional state-space systems is related to the maximum principle for PDE's and it plays notably an important role in the dynamical analysis and control of distributed parameter models of tubular reactors. This talk deals with the stabilization of distributed parameter (i.e. with an infinite dimensional state space) linear systems by
state feedback with a positivity constraint on the state components. The main part of the talk is the description of several methods for computing a positively stabilizing state feedback, under suitable
conditions on the nominal system.
[INMA] 2014-02-18 (14.00) : Predicting opinion dynamics from social experiments on-line
At Euler building
Speaker :
Vande Kerckhove, Corentin
,
and
Martin, Samuel
Abstract :
To what extend is the evolution of human opinion predictable ? How do opinions evolve as a result of social interactions ?
In this talk, we present an attempt to test the consensus system (well known in the control community) as a model of real world opinion dynamics. To gather opinion dynamics data, we built an on-line experiment station. There, participants play social estimation games regarding features in images. To analyze the gathered data, we carried out model identification for several consensus models and correlated model
parameters to personality traits of individuals.
We believe our on-line station to be a promising social engineering tool to investigate human behavior. It allows for a fine tuning of the experiment settings in order to closely fit to the research question.
This project is a join work with the CRAN, the Université Catholique de Louvain and the University of Cambridge.
[INMA] 2014-02-11 (14.00) : Convex approaches to structured sparsity
At Euler building
Speaker :
Guillaume Obozinski (Ecole des Ponts - ParisTech)
Abstract :
Sparse estimation methods are aimed at using or obtaining parsimonious representations of data or models. They were first dedicated to linear variable selection but numerous extensions have now emerged.
In structured sparsity, one attempts to estimate a function which, in a appropriate parameterization, is encoded by a sparse vector; the support (or set of non-zero elements) of this sparse vector is furthermore assumed to present a type of structure which is known a priori. A common approach to the problem is to penalize implicitly or explicitly the structure of the support of the estimated parameter vector.
In this talk, I will review the convex approaches to structured sparsity, some applications
and time permitting a generic optimal convex relaxation for a family of functions
that penalize simultaneously (a) the structure of the support through a general combinatorial set function, and (b) the Lp norm of the parameter vector for an arbitrary fixed p.
[INMA] 2014-01-28 (14.00) : Optimal experiment design for closed-loop identification: solution based on the central moment extension
At Euler building
Speaker :
Gevers, Michel
Abstract :
Optimal experiment design for system identification was a very active research topic in the 1970s : the results at that time focused on the minimization of different measures of the parameter covariance matrix. The research on this topic disappeared from the horizon for more than a decade. In the mid eighties new results became available that focused on quality criteria that took account of the objective for which the model was estimated. These results were based on Ljung's approximate variance formulae for the estimated transfer functions, under the assumption that the model order goes to infinity. Experiment design experienced a sudden revival of activity from around 2003 under a triple influence : the advent of new expressions for the variance of estimated quantities that did not require an assumption of model order going to infinity, the introduction of the concept of « least costly identification design » due to Xavier Bombois et al, and the development of new opti mal design techniques for identification that convert the optimization problem into a semi-definite program that can be solved using Linear Matrix Inequalities. In this talk we shall first review the development of optimal experiment design. We shall then present new results, developed with Roland Hildebrand, that allow one to solve the optimal closed loop experiment design problem, where the optimization is performed jointly with respect to the controller and the spectrum of the external excitation. Our latest results, to be presented at CDC 2013, allow a direct construction of the optimal pair «controller in the loop - external excitation spectrum». They are based on the so-called «central extension» in the classical Carathéodory moment extension problem, one of the most widely studied problems in the theory of stochastic processes; the central extension was initially introduced by Genin, Delsarte and Kamp in 1978.
[INMA] 2014-01-07 (10.00) : Synchronisation du chaos et Ordonnancement pour les réseaux sans fil
At Euler building
Speaker :
Frédéric Launay (Université de Poitiers, France)
Abstract :
Deux thèmes distincts seront couverts dans cet exposé.
Thème 1 : Synchronisation du chaos.
Les propriétés des signaux chaotiques peuvent être exploitées en télécommunication soit pour masquer un signal dinformation (par exemple via un bruit chaotique ou par cryptographie), soit pour la transmission multi-utilisateurs exploitant des codes chaotiques en bande de base ou en bande RF.
A la réception, différentes méthodes basées sur des approches automaticiennes (Observateurs) ou sur des techniques de traitement du signal (Algorithme Génétique) permettent la synchronisation du chaos et la récupération des informations transmises.
Dans cet exposé, nous présenterons différents générateurs chaotique en décrivant les propriétés du chaos et selon la nature du signal (continu ou discrétisé) nous présenterons différentes techniques assurant, dans des conditions spécifiques (bruit gaussien, canal de Rayleigh), la synchronisation du chaos.
Thème 2 : Agrégation de porteuses dans un contexte daccès mobile Hétérogène et gestion de la politique pour améliorer lefficacité de puissance Application à la 4G.
La norme LTE et LTE-Advanced définissent des systèmes de communication très haut débit sans fil permettant la transmission de contenus multimédia riche sur un coeur réseau tout IP. Les paquets IP sont transmis via des canaux logiques en intégrant la QoS (débit, latence, GBR, ...). Celle-ci est estimée en fonction du service demandé (Vidéo, Voix,
). En terme de débit, le LTE-A permettra datteindre théoriquement des débits crêtes de 1Gbps (DL) via une modulation à haute efficacité spectrale (64 QAM), grâce à une transmission MIMO (4x4) et sur une bande de 100 MHz (5 canaux de 20 MHz) par la technique dagrégation de porteuses (Carrier Aggregation).
Toutefois, les limites principales des systèmes de transmission sont dune part imposées par le canal de propagation et dautre part par les ressources spectrales/énergétiques limitées.
Le contrôle de puissance est utilisé sur chaque lien de communication afin doptimiser la puissance transmise en fonction du bruit et des interférences présentes dans le canal (optimisation du SINR) en temps réel. Le contrôle de puissance optimal permet dune part dassurer le QoS dune communication en garantissant le SNR exigé et dautre part diminuer la consommation de puissance des équipements et donc la pollution électromagnétique. Une stratégie peut être lutilisation conjointe de la technique dAgrégation de porteuse et dun contrôle de puissance pour maintenir la QoS en augmentant les CC et en favorisant des modulations à faible valence sur chaque CC permettant ainsi de diminuer la puissance sur chaque CC (SINR plus faible).
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