We’ve all used GNSS whether we realize it or not.
Global Navigation Satellite Systems (GNSS) are a constellation of satellites. They transmit positioning and timing data to GNSS receivers spread across the earth’s surface.
Businesses and individuals can then use this data to determine the exact location of devices. That means they can also figure out the locations of the people using those devices.
But what does the GNSS signal structure look like? We’ll answer that question and more in this guide.
GNSS Coverage and Constellation
A constellation of internationally owned and managed satellites supplies the global coverage afforded by GNSS.
They include Europe’s Galileo satellite, Russia’s Global’naya Navigatsionnaya Sputnikovaya Sistem (GLONASS), and the USA’s NAVSTAR Global Positioning System (GPS) along with the BeiDou Navigation Satellite System which is owned and operated by China.
The performance of GNSS is constantly evaluated and assessed. NOCs (network operations centers) are situated around the world, grade GNSS performance. A few factors determine the grading.
One factor is the accuracy of the data. Another is the integrity of the system (and the chance of anomalous data). Then, there’s the continuity of the system (or lack of interruptions) and availability.
Anyone who has ever had an interest in satellite technology knows that availability is key. It relates to the amount of time the signal fulfills the above criteria.
Regional, satellite-based augmentation systems (SBAS) help to improve the performance of GNSS. They fortify all the factors we just mentioned. For example, the European Geostationary Navigation Overlay (EGNOS) constantly works as an SBAS.
SBAS all bridge signal gaps and improve the overall accuracy and reliability of GNSS and GPS signals. They achieve this by correcting signal measurement errors and monitoring signal integrity and telemetry data.
The GNSS Signal Falls Into Three Categories
There are some very clear categorical characteristics of GNSS signals.
Firstly, there are carrier signals. Secondly, there are PRN (Pseudo Random Noise) codes (AKA C/A codes). And thirdly, there are navigation data signals. All of the signals used by GNSS satellites are based on CDMA (code-division multiple access) with one exception.
That exception is GLONASS because GLONASS uses FDMA (frequency-division multiple-access) instead. According to a presentation by Dinesh Manandhar at The University of Tokyo, the future signals of GLONASS will switch to CDMA.
The modulation schema of GNSS signals. But, they are predominantly BPSK (binary phase-shift keying) and various versions of BOC (binary offset carrier).
The overall resulting signal output, following modulation, leads to an L1 band GPS signal. It’s resistant to rain fade and robust enough for mission-critical operations and an ever-growing variety of use cases.
GNSS is being used for cellular network infrastructure, Global Positioning Systems (GPS), Automatic Vehicle Location (AVL), tracking systems, and navigation, not to mention an array of maritime, aviation, and enterprise (especially oil field) uses.
To learn more about GNSS/INS navigation systems from an industry expert, take a look at CAST Navigation’s INS systems.
GNSS Signals Are Modulated to L-Band
Anyone with an interest in Global Navigation Satellite Systems (GNSS) would wonder what the GNSS signal structure looks like in practice. And now, you finally know!
To summarize, with the exception of GLONASS which uses FDMA, all the satellites in the constellation known as GNSS use CDMA. And, are modulated to a resistant and robust L1 band GPS signal.
If you want to learn more about GNSS read our other articles about this interesting subject.
