1. State Key Laboratory of Rail Traffic Control and Safety, Beijing Jiaotong University, Beijing, China
2. State Key Laboratory of Rail Traffic Control and Safety and the Key Laboratory of Railway Industry of Broadband Mobile Information Communications, Beijing Jiaotong University, Beijing, China
3. Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA, USA
4. Department of Electrical and Information Technology, Lund University, Lund, Sweden
5. Department of Radio Science and Engineering, Aalto University, Espoo, Finland
6. School of Engineering, University of Glasgow, Glasgow, U.K.
7. Purple Mountain Laboratories, Nanjing, China
8. Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Universite Catholique de Louvain, Ottignies-Louvain-la-Neuve, Belgium