1. Centre forWireless Communications, University of Oulu, Oulu, Finland
2. Department of Electrical Engineering, Lappeenranta–Lahti University of Technology, Lappeenranta, Finland
3. Centre Tecnològic de Telecomunicacions de Catalunya (CTTC/CERCA), Barcelona, Spain
4. School of Electrical and Computer Engineering, University of Campinas, Campinas, Brazil