The new 5G mobile radio systems should enable reliable, secure and wireless data transmission. In rail traffic, this will make virtual coupling possible, i.e. the independent and contactless coupling of trains to longer, virtual units during the journey.
Researchers from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) carried out a measurement campaign at the test site of RWTH Aachen University to determine whether trains with a millimetre-wave radio system specially developed for this application can communicate with each other at high data rates and with minimum delay times.
"For safe automation in train traffic, data transmission must function in real time even under the most difficult conditions - such as high train speeds, for example," explains Stephan Sand, DLR project manager and team leader for communications systems. "That's why we've taken a close look at the transmission properties in particular."
As part of their measurement campaign on a rail test site in Aachen, the researchers investigated the transmission possibilities between train wagons over short and medium distances. For the first time in Europe, the researchers were able to carry out dynamic measurements of radio propagation between trains in the millimeter wave band.
The Institute for Rail Vehicles and Transport Systems (IFS) at RWTH Aachen University provided two self-propelled test coaches, enabling the measurements to be carried out under railway-specific conditions. The millimetre wave radio modules were mounted on the couplings of the train carriages. "In addition to the transmission properties, this test setup also enabled us to analyze the influence of train vibrations and the coupling process on the millimeter wave systems," explains Sand.
The tracks of RWTH Aachen University offer a variety of different ambient conditions in a very small space. For example, automatic coupling manoeuvres could be performed in various environments, such as free environments, near the platform and next to trees and bushes, and straight and curved track sections could be compared.
To analyse the transmission characteristics, the millimetre wave signals were recorded with the so-called channel sounder, a measuring device developed by DLR to analyse the propagation of the radio signals. On this basis, safe and fast communication systems can then be developed.
The first results have shown: Communication via millimetre waves is even possible over longer distances of up to 130 metres. This is a promising finding, as even physically coupled train cars will be able to transmit safety-critical data via millimetre-wave radio links in the future, enabling wireless train control and monitoring systems (TCMS).
Wireless TCMS offers many advantages over the currently wired TCMS. First, wireless TCMS offers an additional, extremely secure transmission path to the electrical coupling, which contains more than 100 sensitive electrical contacts. Since the electrical couplings are subjected to high electromechanical loads during coupling and are also exposed to weather conditions, they often fail and need to be repaired. This in turn leads to train cancellations and delays. Since wireless TCMS inherently transmits data contactless, no failure due to electromechanical stress can occur.
5G Ultra Reliable Low Latency Communications (uRLLC) for wireless TCMS also provides precise and reliable distance estimation between trains during coupling. This allows the coupling process to be fully automated with wireless TCMS and 5G uRLLC.