tion you need: Speed equals distance divided by time. When using this formula, we’re solving for distance. This equation is a very simplified version of the calculations; we go into more detail in episode three of our series.
Here’s what we need to know about the formula: Speed is always going to be the speed of light; that’s how quickly a signal travels through space. The time is how long it took for the signal to reach the receiver. We calculate this based on the receiver’s timestamp when it receives the signal, minus the satellite’s broadcast time stamp. Once we have these pieces, we can solve for our distance from the satellite.
The calculation assumes the speed of light, but once signals reach our atmosphere, that speed isn’t completely accurate. So, we call the calculated distance a “pseudorange” -- it’s our estimated range, and we have other calculations to increase the equation’s accuracy.
Let’s visualize this in space. First, we have a satellite in space. They share their position in orbit and the time of broadcast. All satellites have a certain range they can reach. Within that range, we calculate for distance. With that information, we know we are somewhere within the satellite’s range. To narrow down our possible location, we consider other satellite locations. And now, we know we are at the point where all three spheres intersect on Earth. This process is how we apply the equation to determine our pseudorange to satellites, and find our position. But let’s dig deeper and look at the infrastructure that the satellite signal goes through.
At its basics, a satellite broadcasts a signal to a control segment with a ground-based network of master control stations, data uploading stations, and monitor stations. The control segment helps maintain the accuracy of a satellite’s position and timing, and provides an element of quality control to the signal. The satellite signal also travels to the user segment. This segment includes equipment that processes the received signals and calculates your position. These segments make up the whole infrastructure that supports satellite positioning.
Within the infrastructure are pieces of technology that handle the processing of your position. Let’s follow the satellite signal through each piece of technology:
From the GNSS satellite, the signal travels through our atmosphere to GNSS antennas. During its journey, the signal may have weakened or degraded, and antennas help amplify these weaker signals during reception. Next, the signal travels to our receivers where we use calculations to determine position. Further calculations can also occur that counteract the signal’s degradation.
Once the receiver has run the numbers and equations, it provides positioning data to user equipment working in the field. We use this signal in autonomous vehicles, precision agriculture, defense applications, and even in the average person’s cell phone.
An alternative way to consider the signal’s journey is through these steps: from satellites to propagation, or broadcast, or a signal, to reception, computation, and application. This webinar series will further expand on each of these stages, including the factors weakening or degrading signals, the equations used to supplement degraded signals, and more.
But before we get too complicated, the underlying principle of speed equals distance divided by time remains the same. GNSS infrastructure and user equipment build upon this basic equation.
At its most basic level, user equipment includes antennas to receive signals better, and receivers to improve calculations. These technologies can come by themselves, like our receiver boards here, and can be combined in different ways to further finesse calculations, like with our SMART7 antenna shown here. There are also services, software, and firmware provided that facilitate better processing of signals and positioning data.
Thanks for joining me for episode one of our introduction to GNSS webinar series! I’ve introduced you to the underlying equation to determining GNSS positioning and to the global infra