Eli5 why is cell coverage so bad at airports?
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Because you’re in a big concrete building. Cell phone signals can’t go through walls without losing strength.
In addition, airports often contain a very high density of mobile device users. Network congestion might be an issue, especially for airports without a public wifi network.
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The biggest contributor is just the fact that there’s so many people trying to use mobile networks all in one place at the same time.
Wireless networks of all kinds, including the ones that cell phones communicate with, are a bit like big highway roads. The number of lanes is finite. You can get a lot of people through if they take turns using the lanes that there are, but after a critical mass of people all try to use the road at the exact same time, the lanes get clogged, people start to bump into each other, and traffic screeches to a halt in a big jam. The same thing can happen to the airwaves.
Another small contributor will be the design of the airport itself, where you are in it, and where the nearest cell tower for your network carrier is located. Airports with grand, vaulted roofs require a lot of steel structure, which can disrupt the electromagnetic communications used by cell phones if a dense lot of them sit between you and the nearest tower.
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.
Cell coverage is normally fine imo but the issue is bandwidth, or airtime caused by the large number of wireless clients.
With wireless networks such as cellular or WiFi in your home, in order to avoid traffic collisions a protocol called CSMA/CA is used. This stands for carrier sense multiple access collision avoidance.
Each device connected to the radio broadcaster has a specific time frame to broadcast on. The more devices which are connected, the less frequently your device gets the time to transmit or receive. You see this as slower speeds and higher latency.
There is also the potential issue of backhaul saturation. The backhaul is the fibre or copper cable which the cell tower connects back to the internet, there is only so much bandwidth available, usually between 1-10gbps for cities but sometimes less than 100mbps for rural areas. Even if the tower itself has the capacity to serve 2000 devices at once for example, the bandwidth just isn’t there so it’ll slow down to a crawl
Thank you all for the informative answers!! Fly safe.
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