1. Centre Tecnològic de Telecomunicacions de Catalunya (CTTC/CERCA), Castelldefels, Spain
2. School of Information Sciences, Hallym University, Chuncheon, South Korea
3. School of Engineering, The University of British Columbia, Kelowna, BC, Canada
4. Department of Electrical and Computer Engineering, Boston University, Boston, MA, USA
5. School of Computer and Communication Sciences, Ecole Polytechnique Fédérale, Lausanne, Switzerland