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. School of Electronics and Computer Science, University of Southampton, Southampton, U.K.
4. Key Laboratory of Universal Wireless Communications, Ministry of Education, Beijing University of Posts and Telecommunications, Beijing, China
5. School of Information Engineering, Zhengzhou University, Zhengzhou, China