1. State Key Laboratory of Advanced Rail Autonomous Operation and the Beijing Engineering Research Center of High-Speed Railway Broadband Mobile Communications, Beijing Jiaotong University, Beijing, China
2. State Key Laboratory of Advanced Rail Autonomous Operation, Beijing Jiaotong University, Beijing, China
3. Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, USA
4. School of Information Engineering, Zhengzhou University, Zhengzhou, China