1. School of Computer and Information Technology, Engineering Research Center of Network Management Technology for High Speed Railway of Ministry of Education, Beijing Jiaotong University, Beijing, China
2. School of Electrical Engineering and Telecommunications, UNSW Sydney, Sydney, NSW, Australia
3. 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 (HKUST), Hong Kong, China