1. State Key Laboratory of Rail Traffic Control and Safety and the Beijing Engineering Research Center of High-Speed Railway Broadband Mobile Communications, Beijing Jiaotong University, Beijing, China
2. State Key Laboratory of Rail Traffic Control and Safety, 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
5. Department of Electrical and Computer Engineering, The University of Houston, Houston, TX, USA