How does airplane Wi-Fi work


This is a translation of a post on vas3k.ru, made with the permission from author. You can have a look at more professional translations of his articles, such as the one on computational photography or the history of machine translation on vas3k.com

Writing this from 11,335 meters above the edge of Greenland, feels weird. The network is unstable, websites need to be reloaded 2-3 times and the speed doesn’t exceed 64 kb/s because I didn’t pay an extra $19 for a megabyte.

But woah…

I’m sitting in a soft seat which is moving across the sky at 820 kilometers per hour, and I’ll be writing that a satellite from space is too slow at loading my memes?

I decided to find out where does this luxury come from and write a post. Turns out, there are 2 variants.

Variant 1: you’re flying over land

In the USA, almost every airline has Wi-Fi - it is so common there that any american child will make a scandal if they won’t be able to watch Minecraft "Let’s Play"s on the way to their granny in Michigan.

In Europe, Wi-Fi is slowly appearing on the largest airlines like British Airways, Lufthansa, Turkish Airways and Air France. The Wi-Fi technology came here later, and there are lots of low cost carriers who don’t intend on having it.

It’s anyone’s guess as to what will happen in other parts of the world.

When you’re flying over land, the internet is likely coming from a bellow with specially modified cellular towers. And on the plane it is received by antennas on the sides and a bellow, although you’d probably won’t notice them, as planes generally have different antennas all over the place.

The plane is constantly connected to one or more towers to reduce lag. A plane specific problem with this is that because of their speeds dopler effect is becoming quite obvious - what plane might think is 900 MHz might actually be 850 MHz just because it’s flying towards the signal. Engineers had to do something with it, so here’s some homework for you - try to imagine a solution.

The upside of using cellular towers is that they are cheap and you don’t need much of them - in the whole of Europe, there are only about 300 of them. They are connected into one international network called European Aviation Network. In the USA, the same is done by Gogo and the technology itself is called Air-To-Ground, or ATG for short.

Here’s the map of them in Europe. Fans of Ubisoft games can conquer them to advance to the next level.

Internet speeds with ATG are quite good, especially when there are no clouds. Latest generation networks can achieve up to 15 MB/s. They say it is per passenger, but I wasn’t able to locate the exact bandwidth numbers and the user cap.

And the prices are good too: for $3-10 you can watch youtube for the whole duration of the flight, and some airlines like Turkish Airlines are now providing it for free on their continental flights.

Variant 2: you’re above water

Ocean is too big and rough to have cellular antenas everywhere, so satellites needed to come into play. The story of it is actually pretty similar to a regular sattelite dish, like when your grandpa has to watch football.

The main problem of the satellite dish has always been the fact that it always needs to be pointed at the equator, because that’s where all the satellites are. It’s not very convenient, but that’s where they need to be in order to not move relative to the earth, or else catching a signal would have been much harder.

Just now I realized that this knowledge helped me a bunch of times when navigating in unknown towns - just look at the satellite dishes and that’s where the equator is.

However, there’s one small problem when it comes to planes - while your grandpa’s house can’t make a sharp right, an airplane very easily can. This means the dish needs to spin in order to always point at the equator.

Obviously, you can’t just put a huge spinning behemeth on top of an airplane, so engineers had to make slim mechanisms that would fit inside aerodynamic housings. These, unlike the antennas, are pretty easy to spot.

Nowadays, even flatter antennas are appearing, providing even more fuel savings.

That is actually the reason satellite internet doesn’t start working until about 10-20 minutes after departure - the dish’s motors just aren’t turned on as the plane is maneuvering on twisty departure procedures. During the main phase of the flight, however, a small correction every now and then is enough.

Except for the dish, everything is similar to other applications of satellite communications - you send the request in the direction of the satellite, it reflects it back to earth where a special antena catches it and sends it to the internet. It then receives the response and sends it back to you. Every major country already has a network of such dishes.

There’s one fatal flaw with that - the latency. The signal travels such enormous distances that ping under 0.5 seconds just doesn’t exist. Not very gamer-friendly, and we don’t have a solution for it in sight for now.

Sure, there are some weird networking hacks for TCP protocol (data transmission protocol where communicating devices check the data for integrity) where you don’t wait for confirmation of every packet (piece of data), but still have data integrity.

In general, it’s possible to route memes through satellites, but it’s slow and expensive, so you either have to pay $8 for miserably low speeds but use it for the whole duration of the flight or pay extra for a bit less miserably slow megabytes.


Translated by @Alexander_Nikitin with polishing done by @Maxim.
Original article by vas3k

38 Likes

Wow! Very interesting to read!

Crazy how all of this works.

Really refreshing and interesting topic! Thanks for sharing.

Nice work! It explains very clearly!

image

6 Likes

This tops the best thing I’ve seen on the IFC 😂

2 Likes

It’s so true though! Though my grandparents don’t live here, I know so many that do 😂

1 Like

great topic! was always wondering…


also i’m disgusted by this

Such an entertaining and informative post! Keep the good work haha

This is a very interesting article! I think it’s very good that you also inserted pictures that makes it very appealing, and it’s also very cool to see this kind of topics. It’s definitely very cool thanks for posting!

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