By Girish Linganna
Not long ago, when you boarded a plane, you knew you would be completely unreachable for the entire duration of the flight. You had no choice but to relax, read a good book, take a nap, or watch the in-flight entertainment. But, in today’s digital age, more airlines are offering onboard Wi-Fi. This allows passengers to share their trips on social media and lets business travellers use their flight time to work productively.
About 10 years ago, when airplane Wi-Fi first appeared, it was costly and slow, barely enough for a few laptops or Blackberry phones. However, as more people own smart devices, airlines are now looking into—and using—better options to enhance connectivity.
But how does Wi-Fi work 40,000 feet above the ground?
There are two types of airplane Wi-Fi systems
- Air-to-ground (ATG): This acts on signals from ground-based cell towers directed upwards, and
- Satellite Wi-Fi: This depends on signals from satellites orbiting the Earth directed downwards
Air-to-Ground Wi-Fi
ATG works like the Wi-Fi system used for your home or mobile devices. Your device, or router, sends and receives radio signals through its antenna to and from cell towers on the ground. It operates the same way on an airplane. An antenna is installed on the underside of the airplane to receive and send signals to and from cell towers. As the plane flies, these signals are passed on from one cell tower to the next.
The downside of ATG is that it does not work well in remote areas, or over large bodies of water, such as oceans, due to the lack of cell towers. This makes it suitable mainly for land travel, although there may still be some areas without coverage.
Wi-Fi speed with an ATG connection is slow, about 3 Mbps. This is fine for checking e-mail messages or using messaging apps, but it is not good for activities that need a lot of bandwidth, such as streaming videos or uploading files.
The Satellite Wi-Fi
In satellite systems, ground units send signals to a satellite in orbit, which then relays the signal to the airplane. This method offers better connectivity in areas without cell towers, such as over large bodies of water. However, the long-distance which the signals must travel can cause delays that affect Wi-Fi speed.
Aeroplane Wi-Fi can use traditional communication satellites in geostationary Earth orbit (GEO), or newer low-Earth orbit (LEO) satellites, such as OneWeb and Starlink.
The GEO versus LEO
GEO satellites are very large and orbit at a fixed position about 22,000 miles (35,000 km) above Earth. Because they stay in one spot, they cover a specific area. For instance, Viasat’s high-speed satellite for North America does not provide coverage for international flights outside that region.
GEO satellites have high transmission rates where speed and bandwidth are concerned. However, their distance from Earth means they have high latency. This causes a delay between your device sending a request to the Internet, the signal bouncing off the satellite to a ground station, the Internet processing the request, and the response travelling back to you. This can make the connection feel slightly lagged, although providers are working to speed up other parts of the process where possible.
Meanwhile, LEO satellites are much smaller and orbit at about 1,200 miles (1,900 km) above Earth. LEO satellites are just beginning to enter the aviation market. One reason is the small size of the antennas needed to connect to these closer satellites.
Although they have a lower transmission capacity due to their size, their shorter distance results in lower latency, making the response feel quicker. The smaller size of LEO satellites allows more of them to be launched at once. For instance, OneWeb has launched up to 40 satellites per rocket, reaching nearly 600 satellites in orbit after 20 launches.
Ku-Band and Ka-Band are two types of satellite systems. Ku-Band uses frequencies between 12-18 GHz, while Ka-Band operates at 26.5-40 GHz. Generally, higher frequencies mean more available bandwidth.
The Ku-Band
Ku-Band offers faster speeds than ATG connections, around 30-40 Mbps. However, since the satellite signals are shared with other airplanes, the bandwidth may decrease in crowded airspace. While Ku-Band is not the fastest Wi-Fi option, it is the most reliable. With hundreds of Ku-Band satellites orbiting Earth, the airplane’s antenna is more likely to keep a stable signal. When this bandwidth is shared among many users, it typically is not sufficient for streaming content.
OneWeb’s low-Earth orbit (LEO) network uses the Ku-Band to connect satellites to airplanes.
The Ka-Band
Ka-Band is currently the leading technology. Ka-Band offers the most advanced high-speed satellite Wi-Fi, delivering speeds of up to 80 Mbps per airplane. However, there are fewer Ka-Band satellites in orbit, resulting in limited geographical coverage; so, currently, only some airlines can use it.
One of the key advantages of the Ka-Band is its high data transfer rate for satellite communication. It has antennas and components smaller than with other frequencies since it has a short wavelength. Additionally, its bandwidth is twice as large as that of the Ku-Band. In Ka-Band satellite applications, communication capacity and system coverage can be enhanced by reusing frequencies.
The main players in this field are Viasat’s high-speed satellites in North America, which offer slower service through partners in Europe and Australia, and Viasat’s Global Xpress (formerly Inmarsat), which provides global coverage and is preferred by many airlines for international flights.
In-Flight Wi-Fi Setup
In the case of a satellite Wi-Fi system, a dome-shaped container on top of the airplane houses an antenna inside it. These antennas have been made more aerodynamic over time to reduce drag and save fuel. Older antennas had to face the signal direction and used a bulky gimbal to rotate and tilt. The more modern antennas are more streamlined and have the capacity to receive and send signals in a motionless state, saving airlines tens of thousands of dollars annually in fuel costs.
For ATG systems, there are usually a few antennas on the underside of the aircraft, and, sometimes, side antennas to receive and send to ground cell towers signals that are processed by a modem on the aircraft and then distributed to passengers’ laptops or mobiles through wireless access points (WAPs). Typically, one WAP is needed for roughly every 50 passengers.
Girish Linganna is a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd. a subsidiary of ADD Engineering GmbH, Germany.
