1. State Key Laboratory of Advanced Rail Autonomous Operation and the Frontiers Science Center for Smart High-Speed Railway System, Beijing Jiaotong University, Beijing, China
2. State Key Laboratory of Advanced Rail Autonomous Operation and Beijing Engineering Research Center of High-Speed Railway Broadband Mobile Communications, Beijing Jiaotong University, Beijing, China
3. State Key Laboratory of Advanced Rail Autonomous Operation and the Key Laboratory of Railway Industry of Broadband Mobile Information Communications, Beijing Jiaotong University, Beijing, China
4. School of Information Engineering, Zhengzhou University, Zhengzhou, China
5. Department of Electronic and Electrical Engineering, University College London, London, U.K