1. Faculty of Engineering, Free University of Bozen-Bolzano, Bolzano, Italy
2. Faculty of Engineering, Free University of Bozen-Bolzano, Bolzano, Italy and Department of Information Engineering and Computer Science, University of Trento, Trento, Italy
3. Department of Informatics, University of Bergen, Bergen, Norway and Department of Informatics, University of Oslo, Oslo, Norway