1. College of Computer Science and Electronics Engineering, Hunan University, Changsha, China
2. Department of Electrical and Computer Engineering, Stony Brook University, Stony Brook, NY, USA
3. Computer Network Information Center, Chinese Academy of Sciences, Beijing, China
4. School of Computer Science and Engineering, Hunan University of Science and Technology, Xiangtan, China
5. Department of Computing, The Hong Kong Polytechnic University, Hong Kong, China