The interview was conducted by Georg Kern and was first published in bahn manager Magazin issue 02/2024.
Download original interview in German here
Mr Tessmer, everyone has probably experienced this: you want to make a phone call on the train, but the connection keeps dropping. How can it be that this problem still occurs so frequently in 2024?
There are many reasons. They may have their origins in the coverage at the track. Or it could be the train itself. In most cases, it is a combination of several reasons. In addition, unfortunately there is no simple, continuous improvement process possible; new technologies are constantly posing new challenges for mobile phone networks.
On the other hand, mobile phone calls in cars are now quite reliable.
This is in general also confirmed by our measurements. Of course, there is still potential for optimisation there too. But you’re right: mobile phone reception on trains poses completely different and sometimes even greater challenges.
What are the challenges of mobile phone reception on trains?
Just take the sheer number of mobile phones on a passenger train. It can sometimes happen that 400 or more devices can be suddenly rushing into a radio cell within seconds. These are peaks that you first have to adress with special solutions. Another challenge is the nature of the trains, which are actually impermeable to mobile phone signals per se. Targeted measures are required to bring the signal inside the train.
For example, windows are lasered to make them more permeable.
An effective measure: patterns are inserted into the thermal insulation layer of the windows to make them more permeable for the mobile network signals. New trains, especially long-distance trains, are almost never delivered without these windows nowadays. And that’s where we come in: to find out which patterns deliver the best results, many measurements have to be carried out to compare the mobile network quality on the outside and inside.
When you measure the network quality in trains or on railway lines: Who are your clients – the mobile network providers or the train operators?
When we first became active in the railway sector in 2008, our clients were almost exclusively the mobile network providers (MNOs), i.e. Telekom, O2 or Vodafone. In the meantime, railway operators are also increasingly becoming our customers. These include for example Deutsche Bahn and the Swiss Federal Railways.
Why is the trend moving towards railway operators?
People understand how important good network reception is for customer comfort. Passengers want to make phone calls and surf the Internet – also in order to work. This often makes it easier to cope with delays. But other services and operational processes of railway operators are also dependent on radio, such as mobile ticket control, payment by credit card or the digital transmission of departure orders.
Speaking of operational processes – what role does the switch to FRMCS, the successor system to GSM-R, play for you?
This changeover is an exciting topic. To ensure trouble-free operation, possible interferences between operationally relevant systems and the public mobile radio networks must be identified. Our measurement systems are also used here.
What does the typical work order from a railway operator to NET CHECK look like?
It usually involves measuring the mobile network coverage along the track, which we call the external situation, as well as the quality of mobile network reception inside trains. Such an project requires a certain preparation time. After all, our devices have to be installed in the trains.
Do you install your measuring devices permanently in the trains? Why don’t you just walk through the trains with them?
The measurement results would be far too inaccurate. To collect reliable data, you need a large number of measurements taken at defined places. This is the only way to end up with enough reliable, geolocated data that can be compared with each other. Such quantities of data, especially for continuous improvements, can only be recorded by permanently installed systems. Recording with measurement technicians would be far too costly. By using autonomous measuring systems, we can work much more efficiently.
What does such an autonomous measuring device, which you typically install in a train, actually look like?
Our measuring devices contain a commercially available mobile phone that we modify for railway use and control remotely. It is part of our measuring box, which automatically triggers processes such as phone calls or the sending of WhatsApp messages and emails. They also ensure that the mobile phone is running correctly and in continuous operation. The mobile phone can work with different SIM cards to measure the reception of different mobile network operators. These devices measure the network reception inside the train from the customer’s perspective. High-precision frequency scanners connected to a roof antenna are used for the outside situation. The data collected is sent to our head office in Berlin, where it is analysed using software.
Are your devices certified so that they can be installed in trains?
Definitely. Whether in terms of fire protection or electromagnetic compatibility, the requirements for the devices are high and it has cost us a lot of effort to become active in the railway sector. In addition, there are always individual requirements from our customers that have to be met.
What are these individual requirements?
To tell you just one anecdote: When we were commissioned by SBB, for example, we were told that our devices had to be particularly resistant to salt spray.
Against salt spray? But Switzerland isn’t by the sea.
That’s what we thought too. The background to the customer’s request: SBB wanted to take measurements on trains that increasingly carry skiers. They like to hold their ski boots up to the heaters on the train to keep their feet warm. And because the paths to the train are often strewn with salt, salt spray is created, which naturally leads to increased corrosion risks. But we have solved this problem too!
Finally, a political question: the expansion of 5G, the carrier technology for FRMCS, along the railway lines is accompanied by a discussion about the use of technology from the Chinese company Huawei. The technology is said to be of high quality and inexpensive. How do you view this discussion?
In general, there is certainly nothing wrong with independence from components in critical infrastructures that may have interfaces to China. However, the political debate about current technology is often not conducted technical aspects. If we consider the possible effects and costs of retrofitting, other options should also be considered more closely. Firstly, the distinction between passive components such as pure antennas and active network components. The latter are the riskiest components in the debate, but there could certainly be other approaches. For example, a requirement to disclose the source code of the components would be conceivable so that security concerns can be minimised.
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