1. Department of Electrical and Electronic Engineering, University of Cagliari, via Marengo 2, 09123 Cagliari, Italy
2. Consorzio Nazionale Interuniversitario per le Telecomunicazioni (CNIT), Cagliari Research Unit, Department of Eletrical and Electronic Engineering, University of Cagliari, via Marengo 2, 09123 Cagliari, Italy
3. Department of Mechanical, Chemical and Material Engineering, University of Cagliari, via Marengo 2, 09123 Cagliari, Italy