1. School of Computer and Information Technology, Beijing Jiaotong University, Beijing, China
2. Beijing National Research Center for Information Science and Technology and the Department of Electronic Engineering, Tsinghua University, Beijing, China
3. School of Electronics and Information Engineering, Beijing Jiaotong University, Beijing, China
4. School of Electrical and Electronic Engineering, The University of Manchester, Manchester, U.K
5. School of Computer Science and Engineering, Nanyang Technological University, Jurong West, Singapore