The GSM-R:

The GSM-R (Global System for Mobile communications - Railway) is a sub-system of ERTMS (European Rail Traffic Management System).
GSM-R is a wireless communications platform developed specifically for railway communication and applications. It is mainly used to permit communication between train and railway regulation control centers. It is based on GSM transmission system.
GSM-R is a secure platform for voice and data communication between railway operational staff, including drivers, dispatchers, shunting team members, train engineers, and station controllers. It delivers features such as group calls, voice broadcast, location-based connections, and call pre-emption in case of an emergency. This will support applications such as tracking, video surveillance in trains and at stations, and passenger information services.

 

 

The GSM-R uses the following frequencies in Europe:

1. 876,2 MHz — 915 MHz: used for data transmission (uplink)
2. 921,2 MHz — 960 MHz: used for data reception (downlink)

Channel spacing is 200 kHz.

The used modulation is GMSK modulation (Gaussian Minimum Shift Keying). GSM-R is a TDMA (“Time Division Multiple Access”) system. Data transmission is made of periodical TDMA frames (with a period of 4.615 ms), for each carrier frequency (physical channel). Each TDMA frame is divided in 8 time-slots, named logical channels (577 µs long, each time-slot).

Here is an example that explains how the TDMA works:

 

 

 

 

 

 

 

 

The GSM-R is being developed in France by the SNCF and will be operational in a few years.
This system will replace the analog system called "Radio ground/train" which is still used today in 468 MHz.