Whenever railway radio communications are mentioned in a technologically advanced context, the debate tends to quickly gravitate to a single choice: what technology is preferable, GSM-R or TETRA?
The staunchest supporters of each one of these technologies tend to take a slightly dismissive approach to The Other Thing. But the truth, as is often the case, is more nuanced and more complex than some of these discussions would lead one to believe.
With a level-headed, cold-minded reflection, it becomes evident that both TETRA and GSM-R are excellent at what they do: providing reliable radio communications in a railway environment. The choice between the two depends on the characteristics of a specific railway infrastructure, its operational constraints and what the radio system itself is supposed to provide.
TETRA was developed by the ETSI as an open standard with the mission critical PMR market in mind, and has become almost the de-facto digital radio world standard in that environment, presenting an enormous challenge to the competing P25 technology. Being centred in the 400 MHz band, and with a bandwidth of 25 kHz per 4 channels, TETRA is a very efficient and cost-effective way to provide voice coverage to a railway line, and as such has been deployed by many railways around the world.
GSM-R was developed by the UIC with the rail market in mind, evolving from 3GPP GSM technology. Working at higher frequencies (900 MHz or 1800 MHz) and with substantial core architectures, it can be more expensive to deploy than TETRA. However, it can be easily beefed up with GPRS/EDGE to provide data transmission rates in the order of hundreds of kbits/s (TETRA being limited to 3.5 kbits/s net throughput per timeslot). More importantly for railway applications, GSM-R is native to the ERTMS signalling specification, and can support the ETCS Level 2 Euroradio interface without having to resort to supplier-specific proprietary interfaces and maintaining interoperability requirements through an open standard protocol stack.
In short, the optimal choice between these two excellent radio technologies would depend on the integrated, long-term infrastructure plans of a given railway and consideration of all technical and business requirements must be taken before recommending the adoption of either of them.