I. Introduction
High-Speed Railways (HSRs) can improve the quality of rail services, yield greater customer satisfaction, and help to create socioeconomically balanced societies [1]. In HSRs, the train control system plays the key role in providing safe protection and automatic train operation functions during the operation of HSRs. In China, the Chinese Train Control System (CTCS) is divided into 5 levels from CTCS-0 level to CTCS-4 level. So far, the most advanced CTCS-3 train control system uses bidirectional wireless communications to transmit train location information and control commands between onboard equipment and wayside devices, and has been applied in HSR lines where the operation speed is 300-350km/h widely in China [2]. Moreover, Automatic Train Operation (ATO) technology has been applied in current CTCS-3 system in Beijing-Zhangjiakou HSR line to operate the train more efficiently. Compared to degraded train control systems such as CTCS-2 system, which uses balise to transmit unidirectional control information, CTCS-3 can decrease train tracking intervals, increase capacity of HSRs and enhance safety level due to train-to-wayside bidirectional wireless communications. In the future, the more advanced CTCS-4 level train control system would apply higher maximum operation speed over 400km/h and new technologies such as moving block to increase operation efficiency.