GSM-R - Global Standard for Mobile Communications Rail

History

Since the early days of railway communication, every national railway operator has had at least one proprietary radio communication system, mostly in the frequency band of 440 to 470 MHz, but with many different types of modulations, codes and signaling. Due to the fact, that more and more high-speed railway lines were opened all over Europe and the trains crossed many borders on their trips, the need for a unique European radio communication system for railways was raised.

In 1993, the worldwide organization of railway cooperation (UIC, Union Internationale des Chemins de fer) decided for a new system of railway communication. The decision was taken, not to use TETRA for this task but a slightly modified GSM 900 technology. 32 railway operators from 24 European countries agreed in the EIRENE (European Integrated Railway radio Enhanced NEtwork) MoU to roll out GSM-R (-R stands for Railway) networks. GSM-R was finally specified 1999 by ETSI and in 2000 by EIRENE.

Additional Features

GSM-R supports voice connections and data connections through circuit switched data (up to 14.4 kbit/s). Additionally to the GSM call scenarios, because of the high security requirements in railway operations, the following railway specific services were implemented into GSM-R:

• Advanced Speech Call Items (ASCI)
  includes emergency, group and broadcast call services as a means of distributing information amongst a number of GSM-R network subscribers
• Enhanced multi level precedence and preemption (eMLPP) of calls, depending on the subscriber's authorized priority
• Functional addressing
  allows a subscriber in a "function" to be called; this may be the driver's cab. The initiator of the call only has to know the train number; the following steps will be done by the intelligent network within the GSM-R network. The intelligent network then "searches" for the registered subscriber located in the "function" called at the time.
• Location dependent addressing
  offers the caller the means of reaching a duty subscriber, e.g. the responsible dispatcher for the line, at a given location by dialing the same number (for instance a short code number stored in the cab). Depending on the radio cell in which the call initiator is located the call is routed to a specific fixed-line number given. An example: A train driver in the area of City A reaches automatically the responsible dispatcher by pushing the specific dispatcher button on the cab. Passing City B, the train driver is connected to a different dispatcher responsible for that area by pushing the same button.
• Access matrix
  facility for enabling but also for blocking different communication paths. Only the traffic controller, for instance, can reach the train driver as a mobile subscriber. Calling the functional numbers of trains is prohibited for other subscribers.
• Railway emergency calls (REC)
  specific priority communications in an emergency case e.g. for track-to-train radio or shunting radio

Furthermore there will be applications such as diagnostics radio, data transmission for train control and train safety (ETCS).

Technology in brief

GSM-R is based on the GSM 900 standard. It uses different frequencies just below the classic GSM 900 band. GSM-R is also a TDMA system with eight time slots per carrier. A normal speech call uses one time slot; audio is typically transmitted on one time slot per frame. Each base station provides a base channel with basic information about the network and the base station in the first time slot of a carrier.

The in-train GSM-R mobiles are called Cab Radio. They have a special user interface, which is designed for professional railway operators and has some interfaces for communication with train infrastructure, as passenger information systems or diagnostic units.

For railway or shunting workers, there are handsets available, which are very similar to usual mobile phones, but much more ruggedized and with extended functionality.

Typical measurements

Willtek has developed tailor made test applications, which fit to the requirements of the railway operators in matters of test precision and test speed, to enable a short service outage together with the highest operational security for GSM-R Cab Radios.

Due to the high security standard, that is mandatory in railway operations, a number of special call setups (e.g. emergency, group and broadcast call) have to be tested every time a train comes in for a regular maintenance in addition to the standard measurements (Peak power, RMS and peak phase error, frequency error, power vs. time, phase error vs. time and modulation spectrum).

Willtek Test Instruments