1. Institute of Industrial and Control Engineering, Technical University of Catalonia, Av. Diagonal 647, 08028 Barcelona, Spain,
2. Laboratoire des Signaux et Systèmes, CNRS-SUPÉLEC, Plateau de Moulon, 91190 Gif-sur-Yvette, France,
3. Erik Jonsson School of Engineering and Computer Science, University of Texas at Dallas, 800 West Campbell Road, Richardson, TX 75080-3021, USA,