1. Aristotle University of Thessaloniki, Dept. of Electrical Engineering, Division of Electronics & Compo Eng., 54006 Thessaloniki, Greece. E-mail: theochar@vergina.eng.auth.gr
2. School of Electrical & Computer Engineering, Georgia Institute of Technology, Intelligent Systems Lab., Atlanta, GA 30332-0250, USA. E-mail: gjv@ee.gateeh.edu