1. Infocom Department, âLa Sapienzaâ University of Rome, 00184 Rome, Italy.
2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
3. Alcatel Alenia Space Italia, 00131 Rome, Italy.
4. Lunar and Planetary Institute, Houston, TX 77058, USA.
5. Fakultaet fuer Elektrotechnik und Informationstechnik Ruhr-Universitaet Bochum, D-44780 Bochum, Germany.