1. Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece
2. Department of Informatics and Telecommunications, Wireless and Mobile Communications Laboratory, University of Peloponnese, Tripolis, Greece
3. Department of Informatics and Telecommunications Engineering, University of Western Macedonia, Kozani, Greece
4. Department of Engineering and Computing, The University of New Mexico, Albuquerque, NM, USA