1. Dip. Ing. Elettrica ed Elettronica, Piazza d'Armi, 1-09123 Cagliari, Italy
2. Dip. Informatica, Sistemistica e Telematica, via Opera Pia 13, 1-16145 Genova, Italy
3. Dep. of Electrical Eng., The Ohio State University, 2015 Neil Ave., Columbus, Ohio 43210-1275, USA