How it Works: The technology behind satellite internet

Ever wondered how satellite internet works? Here’s a brief outline of how it’s similar in many ways to traditional internet providers, but with a few key differences.


The way most internet works these days is a simple, three-part process: The internet service provider (ISP) gets the internet signal via fiber from a collection of data servers, moves that signal to a central station, or hub, then distributes it to the modems of individual subscribers.

Those first two parts tend to be the easiest to accomplish, while the third — getting the signal to those modems — is the tricky part. That final leg is often called “the last mile,” and for many homes without adequate internet service, it’s that last mile (or multiple miles) from the hub that makes the difference.

If you think about cable or fiber ISPs, they require a technician to come out and wire each location, then connect that to the local hub. Since most homes are already fully cabled, it’s relatively simple to connect all the homes in a neighborhood. If your home is not in a populated area where it makes economic sense for the ISP to serve you with short runs from the hub to your home, it’s less simple. In the case of cable or fiber, it may mean they don’t serve you at all. For DSL from the phone company, they might serve you, but the farther you go from the nearest central station, the worse the service gets.

And that’s why satellite internet became a way to bridge the digital divide for people outside the cable and fiber zone and for those living in remote and rural areas. Satellite ISPs like Viasat work in essentially the same three-step fashion, but instead of a central station, the internet signal is delivered via fiber to a large antenna (called an “earth station”) on the ground, which then moves the signal via radio waves up to our satellite.

In this model, the satellite is functioning like that central office, and that “last mile” is more like 22,300 miles — the altitude at which our satellites orbit. The signal comes back down to your home or office and is captured by an antenna (dish) outside your home that’s aligned with the satellite. From there, the signal goes into a cable through a hole in the wall that connects to a modem — just like any other ISP.


Spectrum & spot beams One of the questions we often hear when talking to new customers is whether they can use the same dish they already have for satellite TV. It’s a good question, but the answer is a firm “no.” The main reason for this is that satellite TV only goes in one direction, broadcasting video signals from the satellite to the home with no “return flight.” Internet signals have to go both ways, and since the signals to and from are not broadcast like video, there’s a much greater amount of bandwidth needed to move all that data. Also, fixed antennas like the ones used for internet and TV all point at different satellites, so it’s not like a TV antenna that can receive different stations on the ground.

That leads to another interesting thing about how we deliver internet via satellite. While the video satellites can broadcast one way in a very large beam that can cover an entire continent, doing so for internet would be a waste of that bandwidth. Think of a radio station at, say, 97.3. If you’re within 50 or so miles of that, you’ll get your local station at that frequency. In the next state over, your rock station at 97.3 might be a country station, because the distance has allowed for a re-use of that portion of the radio spectrum.

Our satellites receive the Ka band of the radio spectrum near 30 GHz and transmit near 20.2 GHz, and we deploy the signal in what are called “spot beams.” These are aimed at specific areas on the ground and they overlap (see illustration). If we’re using the same part of the spectrum for this, then how does that work?


This illustration shows how one-way beams from a video satellite differ from the spot beams Viasat uses to deliver internet with a two-way beam.

The answer is we break down the bands using different polarizations. In case you’re not an electrical engineer, just think of it as different colors. Within a single spot beam, we can use a number of different colors to carry the signal, reusing that same bit of spectrum. Viasat has dedicated quite a bit of effort over the past decade to improving how we do this, and it’s resulted in a highly efficient use of the radio spectrum we’re allocated. This in turn allows us to deliver more bandwidth to all of those modems out there.

As we’ve increased the power of our satellites, we’ve also had to up our game on the ground. Just as more towers equate to better coverage for your smartphone, more of those earth stations adds up to a stronger network for our satellite service. At the same time, moving the processing functions into the cloud has allowed us to create smaller, less-expensive earth stations than we did previously. That helps make it economical to put up quite a few more of them.


We’ve touched on all the main components of how we deliver satellite internet, but there’s one more to mention because it’s something you actually see on your home. What many call “the dish” is actually a couple of different things. The dish itself is just a reflector: a piece of stamped steel aimed at the satellite that works to focus the signal read by the TRIA. This is the metal box at the end of the arm that’s connected via cable to your modem.

“TRIA” is an acronym for “transmit-receive integrated assembly” but all you need to know is that it’s essentially a radio that can send and receive. The TRIA also has a powerful amplifier in it to enable it to push a signal back to the satellite in orbit. Along with your modem, the TRIA is the real workhorse at your location — not the larger dish.

A modem, by the way, serves as the interface between the radio signals received via the TRIA and your computer or router. It also does other things, like authentication to ensure you’re a member of the network and modulate and demodulate the signal.

Even if the basics of how the signal gets to you from the satellite are relatively simple, it does involve a great deal of complex technology to make it all possible. It’s a technology we at Viasat work on constantly to improve. Our goal is to make high-speed internet access possible just about anywhere on earth in the next few years, and hopefully this helps explain how satellite can make it happen.

For a more visual overview of how satellite internet works, take a look at this short video.