Funnily enough, I'm doing a research project relating to mobile phone signal on trains at the moment...
Yes, that's correct.
Typically, it's one modem and antenna(s) at either end of a unit (usually with two different mobile network providers on each modem, typically EE and Vodafone from what I've seen), with the WiFi itself provided by access points throughout the train. But I've also been told that some installations are one modem/antenna/router per vehicle!
Virgin Trains, in partnership with Orange, fitted all of their Pendolinos and Voyagers with mobile phone repeaters for 2G (and maybe 3G, too?). These were switched off in the 2010s and then later removed. I'm not aware of any other UK rolling stock with phone repeaters.
Ofcom's rules meant that there were only a very small number of permitted
static repeaters which could be installed without a license, and that they could only repeat one mobile network's signals at a time. These rules were relaxed, and broadened in May 2022. I don't believe the current rules permit any kind of mobile repeaters (as in, ones which are not in a static location) without a license, which would mean any train operator wanting such a system would have to go directly to a mobile network to achieve this.
All of this is probably why when any potential improvement of mobile networks is wanted on the railways everyone goes for the idea of improving and installing new infrastructure on the mobile network side (plus that means the network gets another meaningful asset rather than the railway!), such as
the new leaky feeder solution for the Gasworks/Copenhagen Tunnels at King's Cross, or
EE & SWR's joint upgrade works on >100 phone masts across the rail network, or the
in-progress Brighton Mainline mobile signal improvement project.
Laser etching windows to make "RF-transparent" glass is a well-established thing now. The first study I could find on its real-world impact was f
rom 2018 by some researchers working at Swisscom's research department who looked at the simulated and actual impact of these glass planes versus the standard ones installed on some of their trains, and showed a rather significant difference in signal strength with treated panes vs coated panes.
View attachment 193269
For some context, -115 dB RSRP is becoming close to unusable, so the fact that treated window panes can pull an in-carriage signal from around -123 dB to -109 dB is pretty impressive. I would say that the UK network would benefit pretty hugely from this. In reality, that didn't account for a
huge difference in throughput in Switzerland, but their mobile networks are far superior to ours over here!
You wouldn't see a running-in board in the UK with two mobile network radios with antennas attached to the catenary supports like you do in Switzerland:
View attachment 193272
Another paper by researchers at ITU Vienna looked at the effect of RF penetration loss in different train carriages too (in this case, OeBB trains) which each had different types of RF-treated window panes and different amounts of window-to-bodyshell ratios. They basically found that more window = more good, but that active repeater solutions were still best.
View attachment 193270
Really, the UK mobile networks have simply got a comparably poor network to most of Europe, and Network Rail have historically caused issues for them to deploy better-sited mobile network towers (mostly relating to interference concerns with GSM-R). Then you have to account for the issues that come with the UK's development/planning legislation. And also the fact our mobile networks are incredibly cheap compared to a lot of European networks meaning there's less capital to reinvest in the networks.
We are trying to get better at things like this, with many Network Rail managed stations gaining distributed antenna systems (such as Victoria, London Bridge, Clapham Junction) but I haven't actually seen any of these
switched on yet... Some already existed at these stations, and some at other stations too, but many have slowly broken and not been fixed, or usage has simply outgrown what they are capable of these days.
Victoria:
View attachment 193278
Victoria also used to have small cells for Orange before the Orange/T-Mobile merger, but these had been switched off for ages and finally disappeared with the Southern gateline expansion. Other antennas were also dotted around the station, but these were either only broadcasting 2G/3G or were simply killed years ago as well.
View attachment 193279
Clapham Junction:
View attachment 193274View attachment 193275
London Bridge:
View attachment 193276
I don't have any pictures of ones at Waterloo, but they also exist there, and are switched on I believe. St Pancras also has a coverage solution throughout the station for EE, but I've run out of attachments.
As an aside, there are issues that are present with LTE (4G) and NR (5G) which make connectivity in high speed travel more complex, but these were forseen long ago and changes have been implemented into later versions of the spec to account for these, specifically like things explicitly called "highSpeedFlag" which will account for issues posed by the Doppler effect. France's mobile network deployments along the TGV network will use these and other tweaked network parameters extensively to provide a tailored experience for passengers on high speed rail. The UK does not use any of these, because networks either do not have the radio optimisation knowledge/understanding to use them effectively, or because they simply don't have any proper dedicated railway deployments that would benefit from it (or maybe both from what I hear!).
