1. Naval Academy Research Institute, 29240 Brest Cedex 9, France. E-mail: {imad.afyouni,cyril.ray,christophe.claramunt}@ecole-navale.fr
2. Department of Computer Science and Systems Engineering, University of Zaragoza, Maria de Luna 1, 50018 Zaragoza, Spain. E-mail: silarri@unizar.es