1. School of Communication and Information Engineering, Chongqing University of Posts and Telecommunications, Chongqing, China
2. School of Information Science and Electrical Engineering, Shandong Jiaotong University, Jinan, China
3. James Watt School of Engineering, University of Glasgow, Glasgow, U.K
4. Mitsubishi Electric Research Laboratories, Cambridge, MA, USA
5. Department of Informatics and Telecommunications, University of Thessaly, Lamia, Greece