1. State Key Laboratory of Rail Traffic Control and Safety, Beijing Jiaotong University, Beijing, China
2. Department of Electrical and Information Technology, Lund University, Lund, Sweden
3. Institute of Information and Communication Technologies, Electronics and Applied Mathematics Université Catholique de Louvain, Louvain-la-Neuve, Belgium
4. Department of Radio Science and Engineering, Aalto University, Espoo, Finland
5. School of Engineering, University of Glasgow, Glasgow, U.K.