1. a Department of Information Engineering and Computer Science, University of Trento, Via Sommarive 14, Trento 38050, Italy
2. b Department of Information Engineering and Computer Science, University of Trento, Via Sommarive 14, Trento 38050, Italy
3. c Department of Information Engineering and Computer Science, University of Trento, Via Sommarive 14, Trento 38050, Italy
4. d Department of Information Engineering and Computer Science, University of Trento, Via Sommarive 14, Trento 38050, Italy;, Email: andrea.massa@ing.unitn.it