[1]ECS-Lab (Laboratoire d' Electronique et Commande des Systeme ) EA3649;
ENSEA (Ecole Nationale Supkrieure del 'Electronique et de ses Applications) Cergy Cedex;
Cergy-Pontoise 95014;
France;
[2]Department of Physics;
Electronic Laboratory;
the University of Yaounde 1;
BP 812;
Cameroon;
[3]EPI Non-A INRIA (Equipe Projet INRIA Non-Asymptotic Estimation for Online Systems);