1. Mobile Radio Communications Laboratory, School of Electrical and Computer Engineering, National Technical University of Athens, Zografou, 15773 Athens, Greece
2. Department of Information and Communication Systems Engineering, University of the Aegean, Karlovassi, 83200 Samos, Greece
3. Department of Biomedical Informatics, University of Central Greece, Papasiopoulou 2–4, 35100 Lamia, Greece