From Quora:
Derek Schatz, I work in aviation and I fly a lot.
Updated Oct 27 · Featured in Forbes
Originally Answered:
What technologies allow airplanes to carry on-board WiFi?
[I used to work for a provider of in-flight WiFi...]
There are two primary methods to enable a passenger Internet connection on an airplane: satellite and air-to-ground. I'll talk about some of the key points on each of those, then talk about the in-cabin WiFi access point part.
Air-to-ground
As the name implies, signals go from the airplane directly to antennas on the ground
Uses a network of ground cell towers across the continental U.S. (therefore does not work over water). These towers' cells are much larger than those of the typical cell towers used for phones.
Uses a version of CDMA, just like Verizon cell phones
Antennas are on the belly of the airplane, looks like a small fin
As the airplane flies, the connection hands off from one tower to the next just like your phone does when you're driving. Users don't notice any interruption.
Network infrastructure is much cheaper than satellite
Bandwidth for the newest generation system (ATG4) is up to 9.8 megabits per second (Mbps) per airplane (shared across all users). This is enough for email and casual web surfing, but would get quickly exhausted if people stream video - so this is usually blocked. See [3] below.
Gogo is the top provider of this type of service [1]
Installed on over 1,000 aircraft operating on domestic routes in the U.S., including Delta, American, Virgin America, and Alaska [2]
Plans announced in late 2014 by Inmarsat to partner with Gogo on a hybrid ATG+satellite solution for Europe
Satellite
Unlike air-to-ground, signals from the airplane go into space to an orbiting satellite and then down to the ground. These satellites are usually in geostationary orbit, 22,300 miles up.
Three types offer different levels of performance (bands indicate specific transmission frequency ranges):
L-band (e.g. Inmarsat Swift Broadband): pretty slow, max 422kbps per channel per airplane
Ku-band (e.g. Panasonic, Global Eagle, and Gogo): tops out at around 20-40Mbps per airplane. Speeds depend on how many airplanes are in the satellite's transponder "footprint" (aka spot beam)
Ka-band (near future, satellites launching soon): promises even higher speeds
A modern satellite has dozens of transponders to support a large number of simultaneous connections, e.g. ships, airplanes, portable ground terminals
Leasing transponders (antennas) on satellites is very expensive, so this cost is usually passed on to the airline and the passengers. But Jetblue offers it for free.
The airplane’s antenna is on the top of the fuselage, under a bubble-shaped radome
Only choice for trans-oceanic routes, and routes flying closer to the polar region (since you can't put cell towers in the ocean)
Using satellites means a few hundred milliseconds more latency since the data packets need to go 22,300 miles up to the satellite, then roughly 22,300 miles back down to the airplane. New constellations of low earth orbit (LEO) satellites providing lower latency high bandwidth connections are in development since 2015, e.g. by SpaceX.
Installed base not large yet but growing, targeted initially for routes between the U.S. and Europe
As the airplane flies, the antenna on the top of the plane is steered or electronically aimed to stay pointed at the correct transponder on the satellite up in orbit. For long-haul flights, there will likely be a handoff from one satellite to another when moving between coverage areas. This happens via coordination on the ground, and the airborne users may only notice a very brief hiccup. From the satellite's viewpoint, it switches airplanes from one transponder to the next as it moves between the beams pointed at the ground.
If you want more technical detail, here is a very nice presentation put together by Panasonic on use of Ku-band for airplanes:
http://airfax.com/blog/wp-conten...
Edit: In support of your sub-question, I should add that the standard TCP network protocol we all use is pretty tolerant of shorter interruptions in network connectivity. This means your session on your email or web server will actually drop pretty infrequently.
In the airplane cabin, there are multiple WiFi access points (WAPs) for passengers to connect to. A large twin-aisle plane may have as many as 6 of these, while a B737 or A320 usually has just 2. From the WAP, the passenger's connection is routed through an onboard server to the satellite or air-to-ground communications system and then goes off board. For both technologies, the goal is to make the passenger's connection as seamless as possible as the aircraft moves through the sky.
Note: In case you're wondering... no, it is not possible to take over control of an airplane remotely over a passenger Internet link. Or any other link, for that matter.
Links:
[1] Gogo’s tech and coverage map: Gogo ATG4 | Gogo Commercial Aviation
[2] Delta:
http://www.delta.com/content/www... ,
American: Wi-Fi and connectivity
Alaska: Alaska Beyond Inflight Entertainment | Alaska Airlines
[3] A nice article on the challenges and the future of in-flight Wi-Fi: How Terrible In-Flight Wi-Fi Will Finally Become A Thing Of The Past
131.8k Views · View Upvotes
Edit:
Link to article
I have not gotten out much this time though, just bought a new (to me) truck and now have 3 houses I am rebuilding after we flooded back in Sept, so trying to spend as little as possible for the rest of the year.
