By Defense AdvancementLast updated: December 15th, 2022
GNSS receivers are ubiquitous and used in a wide variety of military applications. Traditionally, they have equipped military vehicles, aircraft and ships. This reflects GPS, the world’s first GNSS system, being primarily developed for military use.
GNSS use has now spread well beyond the military world into the civilian domain. GNSS receivers have likewise proliferated. They are no longer restricted to vehicles; anyone or anything requiring location or movement details can and does use GNSS receivers.
OEM7600 Dual-Frequency GNSS Receiver by Hexagon NovAtel
A Global Navigation Satellite Signal (GNSS) receiver is any system which can receive an incoming transmission from a GNSS satellite and convert this into usable data. As of 2022, the world has four GNSS constellations. These are the United States’ Global Positioning System, the European Galileo constellation, Russia’s GLONAS system and the People’s Republic of China’s Beidou constellation. All four use the same operating principles. These are articulated in more detail on our Satellite Navigation page.
Satellites transmit a radio signal which includes precise timing information. Provided the GNSS receiver has an uninterrupted line-of-sight to three or more satellites it can receive a distinct signal from each. The receiver then triangulates its position based upon the time it takes each signal to reach the receiver. This process allows the receiver to provide precise position, navigation and timing (PNT) information using these signals.
GNSS receivers are used by a host of static applications. Thanks to the atomic clocks equipping GNSS satellites, GNSS receivers obtain a precise time signal. This is a by-product of navigation requiring the measurement of distance over time. Precise time signals are vital to the digital world and the precise time signal transmitted by GNSS satellites satisfies these requirements.
Military-Grade GNSS Receivers
RIDGE Rugged GNSS receiver in MIL-STD enclosure by Forsberg
All the world’s GNSS systems use radio signals transmitted by the satellites across a waveband of 1.1 gigahertz/GHz to 1.6GHz. GNSS receivers must be able to detect these signals. One challenge for any GNSS receiver is the weakness of the signal once it reaches Earth. GNSS satellites are positioned thousands of kilometers above Earth. This ensures each satellite can ‘see’ as much of Earth as possible. Their altitude means that GNSS signals must travel a very long distance to reach Earth. The satellites have a finite size limiting the electricity generation equipment they can accommodate, and hence the power they can generate. Given the distance the signal must travel, this means it is very weak by the time it reaches Earth.
The weakness of this signal makes it easy to jam (stop the signal outright) or spoof (manipulate the signal to show false data). As a result, military-grade GNSS receivers are designed to accept only encrypted GNSS transmissions reserved for military use. They may also have software to recognise and ignore GNSS jamming or spoofing. While currently the preserve of the military domain, such attributes could migrate to civilian GNSS receivers in the future when they become cost effective.
SAASM GPS Receivers
ZPX-R Passive ADS-B and Mode 5 IFF Receiver System by uAvionix
Unlike commercial Global Positioning System (GPS) receivers, military GPS receivers can deliver secure, Selective Availability Anti-Spoofing Module (SAASM)-based GPS in the most reliable handheld form available.
A SAASM system allows over-the-air rekeying, satellite verification, and contingency recovery, as well as the ability to be updated with an encrypted “Black Key” that can be transmitted over open channels.
In order to get better tracking performance in jamming applications, a higher data rate of the P(Y) code (an encrypted precision code) is needed. To prevent analysis of its internal operations, SAASM hardware is usually covered with an anti-tampering coating.
Military GPS receivers offer benefits such as protection from jamming and spoofing using SAASM and dual-frequency encrypted signals. This type of receiver can be integrated into a vehicle or simply used as a handheld device. It goes without saying that security is vital in military applications, and therefore GPS upgrades, such as the latest M-Code, must provide additional improvements to anti-jam capabilities.