The Magical Science of Wi-Fi on Airplanes

How we browse the internet at 35,000 feet

Credit: Colin Anderson Productions pty ltd/Getty Images

SSurfing the internet at 35,000 feet is now something that we expect on flights. According to the 2018 Global Traveler study, 94% of global travelers feel that inflight internet would enhance their travel experience and 30% of them explicitly look for this feature when booking their flight.

Source: 2018 Global Traveler Study

Currently, airlines make $17 per passenger for services like inflight food and retail. Inflight Wi-Fi will add $4 to this ancillary revenue and is estimated to bring in $30 billion in additional revenue for airlines by 2035.

Given these stats, it’s not surprising to see airlines around the world rushing to add inflight Wi-Fi to their list of amenities. But how does an airline deliver this modern luxury to flyers who are cruising at nearly 560 mph at more than 6 miles above sea level?

There are two ways for the internet to reach planes:

Air to ground (ATG) system

This system, the first to be developed, works like the ground-based mobile data network you’re accustomed to through your cell phone. But unlike mobile towers that focus signal downward, the towers meant to provide internet to planes project them upward. Antennas fitted under the belly of the plane receive the signal and send them to the onboard server. This server has a modem that converts radio frequency signals into computer signals and vice versa, providing access to passengers through the Wi-Fi access points installed inside the aircraft. Information is exchanged between the plane antenna and the towers along the path of the flight. The towers, in turn, are connected to operation centers run by the service providers which are similar to the control centers of your broadband ISP.

Ground-based towers projecting signal upward. Source: ThePointsGuy
GoGo’s ATG-4 System consists of two main antennas under the belly, two side antennas, an onboard server, and a number of Wi-Fi router antennas inside the plane.

The image above shows the ATG-4 system made by the company Gogo, currently the most installed ATG system among U.S. airlines. Gogo’s coverage spans across North America and includes more than 200 towers.

ATG systems have two significant drawbacks:

  1. They operate on a lower frequency (800 MHz), in which peak data speed per flight is limited to 10 Mbps. In comparison, the average fixed-line internet speed in the U.S. is close to 100 Mbps. When multiple users on a flight are logged in, the speed per user is barely enough to check emails and even that would take forever.
  2. The coverage is spotty in areas where there are fewer network towers, like large patches of desert, and nonexistent above water bodies. This makes the ATG system an unpopular choice for international travel.

Satellite system

Inflight Wi-Fi using satellites is more complicated, but also faster and more reliable.

Instead of under the belly of the aircraft, antennas are installed on the top of the plane. These antennas receive the signal from the satellites that are orbiting the earth. But since the satellite and the aircraft are both moving at incredible speeds and are approximately 22,000 miles apart, the antennas need to constantly adjust their position to be able to receive signals. In addition to an onboard server and Wi-Fi access points, a separate device controls the movement of the antenna based on the flight location and speed. The satellites are linked to ground stations which are further connected to operation centers set up by the service providers.

Satellite-based system by GoGo consisting of a satellite antenna, an on-board server, Kandu, to control antenna movements, Modman to convert signals, and multiple Wi-Fi access points within the plane.

The two major advantages of satellite-based inflight internet are:

  1. It’s available everywhere except the North and South Poles. In a long-haul flight, the antennas might have to reposition themselves to connect to a different satellite but typically no more than once. This makes a satellite-based system the obvious choice for international travel.
  2. It operates on higher frequencies which allow more bandwidth and speed. The two main frequencies allocated for satellite internet are Ku-band (12–18 GHz) and Ka-band (26–40 GHz). These two bands allow peak bandwidth between 30 to 100 Mbps per aircraft, which is significantly higher than the 10 Mbps offered by ATG systems.

However, there are three main drawbacks with this system:

  1. It’s more expensive, both in terms of equipment, maintenance, and bandwidth costs than the simple ATG system. This makes the satellite option less popular among smaller airlines and airlines on regional routes.
  2. The distance the data has to travel is extremely high, thus increasing the latency. Latency is the time it takes data to travel between its source and destination in milliseconds. Although the overall speed is faster, when you click on a link, there will be a noticeable delay before the page starts loading, but once it starts it will load almost immediately. ATG systems, on the other hand, will start loading almost immediately because of the lower latency but will take a significant time to complete. Here is an infographic showing the mind-boggling distance the data travels (nearly 45,000 miles).
  3. In addition to equipment, installation, and maintenance costs, the other hidden cost posed by an inflight Wi-Fi system is fuel costs. While it might seem trivial, the change in shape caused by the antennas installed on the outside of the plane puts the aircraft at an aerodynamic disadvantage. This increases drag, which increases fuel consumption. Currently, service providers are working toward reducing the size of the antenna to decrease this cost. Gogo’s latest 2Ku antenna is less than 4 inches thick, creating a much smaller bump.

The major providers of the satellite-based system are:

  1. Gogo leverages satellites owned by Inmarsat to provide Ka-based satellite connection and Intelsat and SES to provide a Ku-based connection. The company’s latest and best offering is the 2Ku system which uses two antennas instead of one—one for uplink and one for downlink—promising speeds up to 100 Mbps per aircraft and 15 Mbps per user. Airlines around the world are quickly adopting a system that enables one of the most sought after features by passengers — video streaming. Airlines that currently use Gogo’s systems include Alaska, American, Delta, United, Virgin America, Cathay Pacific, British Airways, and Japan Airlines.
  2. ViaSat has been providing the faster Ka-band internet to JetBlue flights in the U.S. since 2013. Currently, JetBlue’s FlyFi is industry-leading in terms of speed and affordability. The airline offers Wi-Fi at speeds up to 20 Mbps for free.
  3. European Aviation Network (EAN) is a partnership between Inmarsat, which also operates GX Aviation (the only global Ka-band based satellite service), and Deutsche Telekom. EAN has started providing inflight internet to European airlines. The service uses a combination of both, a satellite-based system for downlink and an ATG system for uplink, to provide a faster (lower latency) and more reliable connection. This system is also known as Ground To Orbit (GTO). Inmarsat owns the satellites, whereas Deutsche Telekom has installed over 300 LTE-towers across the EU. EAN promises speeds faster than all other current inflight Wi-Fi systems.

These aren’t the only providers. Travel site, eDreams has a nonexhaustive list of airlines that offer Wi-Fi on-board.

Economics of inflight Wi-Fi

  1. Some service providers (like Gogo) set the price, handle customer experience, and collect the revenue, sharing a portion of it with the airline.
  2. Some airlines collect the revenue and pay the service provider wholesale prices for the bandwidth used.

With the exception of a few rare airlines that offer complimentary access to Wi-Fi, most see this as a revenue-generating opportunity and not just a perk. While the cost of delivering internet midair is undoubtedly high, airlines add their own margin to this amenity, knowing that their business customers, whose employers foot the bill, will subscribe to this service. Despite only a few passengers opting for this service, the high price, which can be anywhere in the range of $15 to $20 per flight or $600 for an annual pass, allows airlines and internet service providers to cover costs.

Some airlines, like JetBlue, foot the bill themselves by offering it for free to their passengers as a differentiator in the highly competitive market. Many airlines also give their high-tier customers complimentary access to maintain their loyalty, and other airlines find a corporate sponsor that will cover costs in return for running ads on the network.

Airlines also save on the cost of bandwidth by implementing image and audio compression filters that reduce the amount of data consumed.

Airlines can install ATG systems overnight and satellite-based systems in only a few days. EMBED VIDEO

What’s next

The future of inflight Wi-Fi looks faster and more reliable. High throughput satellites will use the given satellite frequencies more efficiently and by employing a new antenna technology that relies on spot beams rather than wide beams. Traditional satellites use a wide beam that can cover areas as large as a country with just a single beam. The obvious disadvantage of this is that all flights within this beam have to share the bandwidth. With spot beam, HTS satellites can focus on a single aircraft and multiple such beams can be broadcast by the satellite, enabling much higher bandwidth per aircraft. Gogo is also currently working on bringing 5G service to ATG-equipped aircraft in the U.S. and Canada by the year 2021.

With better satellites, better antennas, and more service providers jumping into the game, you will soon have the same internet freedom in the air as you do in your home. Sadly, this also means you will no longer be able to use the excuse of flying to justify not replying to all of those emails.

freelance technology writer |

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