1. School of Information and Software Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China
2. Communication Technology Research Center, Harbin Institute of Technology, Harbin 150000, China
3. Department of Electrical and Computer Engineering, McGill University, Montreal, QC, Canada H3A 0G4
4. Department of Computer and Telecommunications Engineering, University of Western Macedonia, Greece
5. Lulea University of Technology, 193187 Lulea, Sweden