It is time to write the acknowledgments. I will do my best. First of all, I would like to show my gratitude towards my supervisors, Mr. Belkacem Ould-Bouamama and Mr. Rochdi Merzouki for providing me with the opportunity to work on this interesting topic. Without whose support, availability, encouragement and fruitful discussions, I would not have achieved the results I obtained in my Ph.D. thesis. It was through his persistence, understanding and kindness that I always worked with enthusiasm. My gratitude also goes towards Mr. Taha Boukhobza and Mr. Eric Bideaux for their availability and interest on reviewing my work. I express to them my deepest appreciation. I also thank Ms. Geneviève Dauphin-Tanguy, Mr. François Charpillet and Mr. Mohamed Djemai for agreeing to be part of the jury of this thesis. Thank you to doctoral and post-doctoral researcher at the Laboratoire d'Automatique, Génie Informatique et Signal (LAGIS). With them, I was able to share the joys and difficulties faced during a Ph.D. thesis. More specifically, I would like to extend very special thanks my office colleagues Samir Benmoussa and Youcef Touati for the helpful discussions and their useful suggestions during these three years.Thank you to all persons who were not mentioned above, but were involved with our work, directly and indirectly.Finally, thanks to my family for the support they provided me through my entire life. I must acknowledge Alice, without whose encouragement and assistance, I would not have worked serenely.