1. State Key Laboratory of Integrated Services Networks, School of the Telecommunication Engineering, and the Guangzhou Institute, Xidian University, Xi’an, China
2. School of Electronics Engineering and Computer Science, Peking University, Beijing, China
3. Graduate School of Information Technology and Telecommunications, Inha University, Nam-gu, Incheon, South Korea
4. Department of Electrical and Computer Engineering, San Diego State University, San Diego, CA, USA