1. State Key Laboratory of Rail Traffic Control and Safety; Beijing Jiaotong University; Beijing China
2. School of traffic and transportation; Beijing Jiaotong University; Beijing China
3. Beijing Research Center of Urban Traffic Information Sensing and Service Technologies; Beijing Jiaotong University; Beijing China
4. Department of Computer Science, Center for Secure Information Systems, Volgenau School of Engineering; George Mason University; Fairfax VA USA