1. School of Computer Science and Engineering, Central South University, Changsha, China
2. Purple Mountain Laboratories, Nanjing, China
3. College of Electronic and Information Engineering, Nanjing University of Information Science and Technology, Nanjing, China
4. School of Information and Communication, Hunan Post and Telecommunication College, Changsha, China
5. Department of Computer Science and Technology, Tsinghua University, Beijing, China