Eli5 why is cell coverage so bad at airports?
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In many cases, it’s not. There are a number of factors to consider:
**In the terminal buildings:**
Cellular coverage is essentially impossible in any medium or large building if it’s dependent on regular outdoor towers. As a result, most airports (as well as many office buildings, especially mid / high-rise towers) and stadiums, arenas, etc. will have additional infrastructure in the building, called a Distributed Antenna System (DAS). These come in many different flavors – some are installed by contractors for a specific operator, some are neutral and can provide signals for all of the available operators. They typically look like WiFi access points on the ceiling, and they provide very localized cellular coverage to that part of the building. They all connect back to a hub of some sort, and on to the “real” cellular network(s) from there.
These systems can provide excellent coverage, even in high density indoor spaces. Anecdotally, I’ve seen many Internet speed tests inside airport buildings delivering 1.5Gbps+ to a phone on a modern 5G DAS.
**Inside aircraft on the ground:**
This is a hugely variable environment. Some modern aircraft (like the Boeing 787 series) have self-dimming windows that do an excellent job of blocking cellular signals, and it can be really difficult to get a reliable signal on the ground even if there is excellent coverage in the area. Also, once you’re outside of the purpose-built cellular infrastructure in the buildings, it’s harder for the networks to support the density of hundreds of users connecting from very localized spaces.
In general you’ll see lots more cellular infrastructure on and around the exterior of airports to support this density, but it can still be a limitation. It can also take some time for phones to find the best towers to connect to if they’re turned on at a new location (like after landing) so that can result in further issues.
Overall if the infrastructure is built well, airports should be areas of excellent coverage. But if any of these pieces aren’t done right, then you can see many issues due to the high density of users.
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