These days, I’d say that the majority of underground metros do have 4G and 5G network coverage. There are a few inglorious cities that haven’t gotten their act together for years now, but let’s not talk about them today. Let’s rather talk about the positive examples, i.e. those metros that have gone the next step.
I call those metros the “Streaming Approved Metros”, because they have done two things right: First, they offer continuous coverage in the tunnels between stations and they have enough carriers on air to allow for a proper data rate for streaming during peak hours. So here’s Düsseldorf, Germany, where I’ve been recently. When I ran a quick speed test in the metro in between platforms, I got a speed of well over 100 Mbps in the downlink direction and an equally satisfying result in the uplink direction as well. From a frequency and carrier point of view, I could get LTE 4 Carrier Aggregation with band 3, 3, 8 and 1 on air (2x 1800 MHz, 900 MHz and 2100 MHz), with a total carrier bandwidth of 60 MHz. In the uplink direction, 3C carrier aggregation was active with 30 MHz. Yes, that’s how it is done!
But, of course, it’s only a matter of time until usage rises to a point where more capacity is needed. Any substantial increase will only come from 5G band n78, i.e. a carrier that can supply extra bandwidth of up to 100 MHz. Let’s see if planers have had the foresight and the money to already prepare leaking cables and other equipment for the 3500 MHz band.