[1] Univ Padua, Dipartimento Ingn Informaz, RREACT Grp, I-35131 Padua, Italy
[2] Ist Nazl Fis Nucl INFN, I-35131 Padua, Italy
[3] Tech Univ Carolo Wilhelmina Braunschweig, Inst Comp & Network Engn, IDA, D-38106 Braunschweig, Germany
[4] Ball Aerosp Technol Ctr, Boulder, CO 80301 USA
[5] CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA