1. Department of Electrical and Electronic Engineering (DIEE/UdR CNIT), University of Cagliari, Sardinia, Italy
2. Department of Computer Languages and System, University of the Basque Country (UPV/EHU), Bilbao, Spain
3. Department of Communications Engineering, University of the Basque Country (UPV/EHU), Bilbao, Spain
4. Department of Electronic Technology, University of the Basque Country (UPV/EHU), Bilbao, Spain