Berlin did not have mobile connections inside the tunnels until very recently (this year, I believe). This included the trains not being connected to any outside network. Thus wifi on the subway was useless to implement.

They did if you were on o2, that's why I'm still with Aldi Talk (they use the o2 network); they've had LTE through the entire network for a while now. The new thing is 5G for everyone.

Despite Berlin's general lack of parity with modern technology, I've never actually had a problem with internet access across the ubahn network in the past decade. I noticed that certain carriers used to have very different availability when travelling and so switched to a better one, but I was always surprised at being able to handle mobile data whilst underground.

Really? I don't even get consistent internet on the Ringbahn. There are lots of holes in the coverage in Berlin.

Which provider are you with? Vodafone is still dead in large parts of the U-Bahn, but I know that one of them works much better.

used to have spotty coverage underground with vodafone, when i switched to telekom, internet suddenly magically worked underground on the routes i used.

I believe someone published a map of the data coverage of different providers on the berlin ubahn, but probably outdated now

Yeah, admittedly this year I've also started experiencing holes on the ringbahn (strangely and consistently around frankfurter allee), but the ubahn has been fine.

I'm with sim.de which I believe is essentially an O2 reseller (apn references o2)

Gesundbrunnen too.

Wow! I was in Berlin last week and kept losing connection... like all the time. I use 3 with a Swedish plan. In Sweden, it literally never drops, not on trains, not on metro, not on faraway mountains... it works everywhere.

I was in Berlin earlier this month and the cellular connections underground were quite good now. So maybe this is less of a problem?

It's provider-specific

Not any more? https://unternehmen.bvg.de/pressemitteilung/grossprojekt-erf...

Summary: since 2024-05-06, users of all networks also get LTE in the U-Bahn thanks to a project between BVG and Teléfonica (not surprising that Teléfonica deployed the infra because they had the best U-Bahn LTE coverage beforehand)

Yes, right now it's mostly just wifi at stations only. However, they're deploying 4G/5G coverage in the tunnels and expect 80% coverage by the end of 2024 [1].

So… you can expect apps developed by engineers in London to get much worse on slow internet in 2025. :-)

[1]: https://tfl.gov.uk/campaign/station-wifi

WiFi at a stop is as easy as putting up a few wireless routers, it's a bit more complex than at home but the same general idea.

Wifi inside the trains involves much more work, and to get them to ALSO be seamless across the entire setup - even harder. Easily 10x or 100x the cost.

It's sad, because the Internet shouldn't be that bad when the network drops all the time; it should just be slower as it waits to send good data.

I think they just put a wire in the tunnel.

Yes, that's the best way which is often used. A "leaky cable" aka "leaky feeder", to be particular.