School of Computer and Information Technology, Beijing Jiaotong University, Beijing 100044, China;
School of Computer and Information Technology, Beijing Jiaotong University, Beijing 100044, China;
School of Computer and Information Technology, Beijing Jiaotong University, Beijing 100044, China;
the State Key Laboratory of Rail Traffic Control and Safety, Beijing Jiaotong University, Beijing 100044, China;
the Key Laboratory of Broadband Wireless Communication and Sensor Network Technology of Ministry of Education, Nanjing University of Posts and Telecommunications, Nanjing 210003, China;
Nokia Bell Labs, Beijing, Beijing100044, China;