The rail infrastructure of the train technology is divided into line sections, so-called block sections. The previous signaling system prevents the double occupancy of block sections. In contrast, Communication-Based Train Control (CBTC) is designed as a flexible mobile movement block system.
The block section system previously used in rail infrastructure is an aging signaling system in which the number of trains is limited by the fact that only one train is in a block section at a time. Advanced, more flexible approaches can increase train frequency by allowing multiple trains to pass through a block section. Appropriate techniques with position detection can be radio-based, as in Communication-Based Train Control (CBTC), with highly accurate location determination of trains. Bidirectional train-to-train communication takes place between the trains via infrastructure components, comparable to roadside units in road traffic. The trains constantly communicate their location, direction of travel, speed and braking distance to infrastructure components located along the train route. These components serve the automatic train protection ( ATP) functions. The distance between trains is determined from the transmitted and other data and their speeds are adjusted.
CBTC systems consist of various components located on the train and on the track. Onboard systems, those located on the train, include the onboard ATO system, which stands for Automatic Train Operation (ATO), and governs transaction and braking controls. The ATO system located on the track is called the Wayside ATO system, and provides information about remaining travel time and stops at stations, among other things. For communication between trackside equipment and trains, there is a radio network that operates in license-free and license-required frequency bands.