Intro to GNSS Episode 1 – The Calculations Underlying GNSS

Our on-demand webinar series begins with James Chan, the North America team lead and core customer support at Hexagon’s Autonomy and Positioning division, explaining the underlying calculations GNSS technologies use to determine positioning. This presentation, the first of seven, is designed to give you a foundation in understanding GNSS (Global Navigation Satellite Systems). This presentation explains the underlying math and measurements used to calculate positioning anywhere in the world.

With this calculation, we can determine our “pseudorange” -- our estimated distance from your location to the satellite. It’s estimated because of the influence the atmosphere and other variables can have on a truly accurate calculation.

The infrastructure around satellites is a complex system designed to keep timing, orbit location, and calculated positions as accurate as possible. First, 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, providing some quality control to the signal. Next, 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.

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. Future episodes of our Intro to GNSS webinar series will explore positioning calculations, error sources and resolving errors, GNSS denial, and much more.

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