oning can be augmented with other external sensors like inertial navigation systems that help provide additional data to supplement an accurate position. We will explore these technologies in more detail in episode four of our series.
Thanks for joining me for episode two of our introduction to GNSS webinar series! We’ve explored the factors that can affect satellite signals and result in positioning errors and we’ve introduced the technologies that can mitigate them. Our next video examines what happens to the satellite signal once it reaches the receiver. We’ll share some of the calculations used to compute an accurate position. But, if you’re ready to get a head start in learning these GNSS concepts, download our in-depth book An Introduction to GNSS.
Episode three of our on-demand webinar series features Hexagon | NovAtel Technical Marketing Specialist Paul Verlaine Gakne explaining how satellite signals are received and processed to output a position. We include a transcript below.
Hello, and welcome to episode three of Hexagon NovAtel’s webinar series on An Introduction to GNSS. My name is Paul Verlaine Gakne; I’m the technical marketing specialist at Hexagon’s Autonomy and Positioning division. Thanks for joining me!
Today, we’ll illustrate the components of a satellite’s signal, how it’s received by antennas, and what happens when the signal is processed by receivers. We’re scratching the surface, so if you’re ready for a deeper look at GNSS concepts, you can download our Introduction to GNSS book.
We’ve explained that satellites transmit signals, but let’s go into more detail. GNSS refers to global navigation satellite systems, which includes four main groups of satellites known as constellations: GPS, GLONASS, Galileo, and Beidou. Each constellation is managed by a different country, and they each have their own idiosyncrasies. To transmit information, satellites use radio frequencies allotted to GNSS, and each constellation broadcasts on at least two frequencies. For example, GPS broadcasts at L1, L2, and L5 frequencies.
Radio frequencies are used to send satellite system data, timing, status and other information needed for accurate ranging. The satellite combines and modulates this data onto the carrier wave which is then transmitted toward Earth.
What a signal is made of
A GPS signal is made up of a unique identification code, known as the PRN code, which is used to range from a satellite to the receiver and a Navigation Message that contains satellite health, status, time and orbital information. The PRN code and navigation information are combined, and then modulates that onto the carrier wave. What results is a modulated signal that gets sent down to the receiver. Knowing how the data is superimposed onto the carrier signal, the receiver can extract the required information to range to a satellite from the modulated signal.
From a satellite, signals pass through the atmosphere towards the antenna, which senses, receives, and amplifies the satellite signal. Signals can be faint after travelling from space to Earth, so choosing the correct antenna for your application is important. Having an antenna that can receive multiple signals from multiple constellations increases the accuracy and reliability of your positioning – more access to satellites means you have more data to inform your equipment.
Our book, an Introduction to GNSS, goes into detail about antenna selection to choose the right product for your environment and application.
Once the antenna has received, amplified, and converted the radio frequency signal from a satellite, the signal is processed by receivers to de-modulate, unpack and separate the data provided. Then, the receiver outputs positioning as latitude, longitude, and height data.
Through complex equations, the receiver resolves for positioning errors and atmospheric delays, and calculates a position or more specifically geographic coordinates. With additional algorithms, receivers can also gather supplemental navigational data from other sensors.
How a GNSS receiver works: Pseudoran