Without a mechanical connection: virtual coupling of trains via ultra-wideband

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Increased automation in rail traffic could increase the capacity of the existing rail network. A key technology for this is virtual coupling, in which individual trains or wagons are no longer connected mechanically, but purely digitally. They travel one behind the other at a fixed, very close distance. For this to work smoothly, the train sections must continuously exchange data about their position and speed. The German Aerospace Center (DLR) has developed a new type of radio system for this purpose as part of the R2DATO project, funded by the EU with almost 54 million euros, and has now successfully tested it on a test site.

The DLR Institute of Communication and Navigation involved in R2DATO focused on decentralized communication between trains that are near each other. "We are talking about distances of twenty to two hundred meters that are required for virtual coupling", explains DLR project manager Paul Unterhuber. "That's extremely close for the rail sector." This is because, depending on the speed, braking distances can be "several hundred meters to a kilometer long".

UWB: Precise distance measurement at short distances

The system developed by DLR uses ultra-wideband communication (UWB), a radio technology that uses an extremely broad frequency spectrum for data transmission. It enables high-precision positioning and data transmission over short distances. UWB is already used in smartphones, indoor and industrial tracking devices and car keys, for example.

"Another advantage of UWB is that it enables the distance between two trains to be calculated very accurately," reports Unterhuber. To do this, the institute uses the latency time that data packets require from the transmitter to the receiver. This means that all the necessary information is available "to control acceleration and braking processes in the close range that is important for virtual coupling".

The system also has a laser-based reference system that also measures the distance between the trains. It helps to check the accuracy of the UWB measurements. All components are powered by batteries. R2DATO has nothing to do with the parallel "digital automatic coupling" project.

First test on tracks in Holland

The first tests took place on a 350 meter long track of the Dutch State Railways (NS) in Amersfoort. Two regional trains equipped with the DLR system covered the route several hundred times. The crucial technology was located in compact boxes attached to the mechanical couplings of the trains. Another unit on the ground served as a base station for data collection.

The trains simulated various scenarios at speeds of 10 to 25 kilometers per hour, with distances of between 15 and 80 meters. Scenarios in which one train was moving and the other was stationary were also simulated. The trains were controlled by train drivers, which was not easy to master due to the small distances. The DLR team provided them with live information from the system on a separate monitor. In the future, this data should contribute to largely automated or autonomous train operation.

Feasibility of the concept demonstrated

DLR describes the test results as promising: the distance between the trains could be determined to within a few centimetres, which is not possible with previous technologies in the rail sector. "In general, we were able to show with the tests that the communication between the trains and the distance calculation based on this also works in practice in a near-railway environment," says Unterhuber happily. The collected data will be further evaluated. R2DATO is coordinated by the French rail operator SNCF. Deutsche Bahn, ÖBB, the Italian state railroad and various suppliers are also involved.

The DLR Next Generation Train (NGT) concept, which was developed as part of rail transport research, also relies on virtually coupled train formations. An "NGT cab" is intended to enable automated operation on branch lines and make them more attractive again. It could respond as needed – with virtually coupled wagons – to the number of passengers currently willing to travel.

(nie)