1. Engineering Research Center of Network Management Technology for High Speed Railway of Ministry of Education, School of Computer and Information Technology, Beijing Jiaotong University, Beijing, China
2. Department of Electrical and Computer Engineering, University of Victoria, Victoria, BC, Canada
3. Department of Electronic Engineering, Beijing National Research Center for Information Science and Technology, Tsinghua University, Beijing, China
4. Department of Electrical and Computer Engineering, Hong Kong University of Science and Technology, Hong Kong, China