An introduction to global navigation satellite systems (GNSS)
Every hour of every day, we’re surrounded by radio waves. While some transmissions like TV and radio entertain us, others such as GPS provide invaluable information that we would quite literally be lost without. And yet despite the importance of GPS in our daily lives, we generally understand very little about how it works.
Here we will shed a little light on the subject of satellite navigation. We will go deeper than some explanations, but avoid the complicated things only system engineers need to know. By the end, you’ll have strong understanding of how satellite navigation actually works, and more importantly what it can, and can’t, do for you.
What is GNSS?
The term GPS is now so familiar to the general public that it has become synonymous with any satellite navigation system—but we need to be careful. The term GPS is actually the name of the system created by the American military, and stands for Global Positioning System. There are other systems too. The Russian military system for example is called GLONASS (Global Orbiting Navigation Satellite System), while China has developed a system called BeiDou-2.
When talking about satellite navigation systems, a term you will often encounter is GNSS, which stands for Global Navigation Satellite System. This is the generic name used to describe any global system of satellites that transmit signals for navigation purposes on Earth. The distinction of using terms like GPS or GLONASS is important if you’re using satellite systems for measurement purposes because each system works in a slightly different way (although the end result appears to be the same).
As of 2020, there are four main GNSSs:
- GPS. America’s Global Position System.
- GLONASS. Russia’s Global Orbiting Navigation Satellite System.
- BeiDou-2. A system developed by China.
- Galileo. A system developed by the European Union.
In order to answer, ‘What is GNSS?’ we need to ask – and answer – a series of related questions, and explore related topics as set out below:
How does a GNSS receiver work?
There are two parts to most GNSS receivers; the antenna and the processing unit or receiver. Read on to learn more.
How does a GPS receiver work out where I am?
Today, we take for granted that the phone in our pocket can tell us where we are. But how does a GPS receiver calculate our position? We explain here.
The GPS signal
The hardest part of understanding GPS is the signal itself. This article explains the key things you need to know.
Finding satellites
The first thing a receiver needs to do when it’s powered up is look for satellites. How does it find them? We explain here.
Working out the range to a satellite
Each satellite in the GPS constellation transmits a unique C/A code, which appears to be random noise, but is in fact a deterministic sequence. How do we use this to work out the range to a satellite? We explain here.
Trilateration
Once we know the distance to each satellite, how do we use this information to help work out our location? Click here to learn about trilateration.
SPS
The term SPS stands for Standard Positioning Service. Learn how SPS provides the lowest accuracy GPS position measurements here.
DGPS
What are differential corrections or DGPS? Learn about error factors and explore ways to correct them here.
What is RTK?
RTK stands for Real-Time Kinematic and is another technique that improves the accuracy of GPS position measurements. Read this page to learn why it’s one of the hardest to understand and the most intensive to implement.
What are the limitations of GNSS?
Does DGPS or RTK most improve the accuracy of velocity measurements? GNSS systems don’t drift and can achieve high levels of accuracy, so what are the limitations of GNSS systems? Find out here.
