1. Department of Electrical Engineering and Information Technology, University “Federico II” of Naples, 80125 Napoli, Italy;
2. Department of Electrical Engineering and Information Technology, University “Federico II” of Naples, 80125 Napoli, Italy
3. Istituto di Analisi dei Sistemi ed Informatica Antonio Ruberti, Consiglio Nazionale delle Ricerche, 00185 Rome, Italy