1. School of Information and Electrical Engineering, Hebei University of Engineering, Handan, China
2. School of Computer and Communication Engineering, University of Science and Technology Beijing, Beijing, China
3. Chongqing Key Laboratory of Mobile Communications Technology, Chongqing University of Posts and Telecommunications, Chongqing, China
4. Department of Computer Science and Engineering, Kyung Hee University, Yongin-si, Republic of Korea
5. Department of Electrical and Computer Engineering, University of Houston, Houston, TX, USA