1. Department of Computer Science, Multimedia and Telecommunication, Universitat Oberta de Catalunya, 08018 Barcelona, Spain
2. Spindox España S.L., Calle Muntaner 305, 08021 Barcelona, Spain
3. Department of Applied Statistics and Operations Research, Universitat Politècnica de València, 03801 Alcoy, Spain
4. Department of Telecommunication and Systems Engineering, Autonomous University of Barcelona, 08202 Sabadell, Spain