What communication technology is predominantly used for train positioning in CBTC systems, and why?

Wi-Fi or radio communication, often using specific frequencies allocated for railway use, is predominantly used for train positioning in CBTC (Communication-Based Train Control) systems because it allows for continuous, two-way communication between the trains and the central control system, enabling precise and real-time location tracking. CBTC systems rely on knowing the exact location of each train on the network to maintain safe separation and optimize train movements. This continuous communication link enables the central control system to determine the precise location of each train, typically using a combination of onboard odometry (measuring wheel rotations), transponders or balises along the track, and potentially GPS or other positioning technologies. The data from these sources is fused together to provide a highly accurate and reliable estimate of the train's position. Wi-Fi or radio communication provides the necessary bandwidth and low latency for transmitting this positioning data, as well as other critical information such as speed, braking status, and passenger load, between the trains and the central control system. This continuous, two-way communication is essential for implementing advanced CBTC functionalities such as moving block signaling, which allows trains to operate closer together than traditional fixed-block signaling systems, thereby increasing capacity and improving efficiency. Unlike systems that rely on discrete location updates, continuous communication provides a constantly updated picture of train location, enabling safer and more efficient operation.