Hexagon | NovAtel Business Development Manager for Defense and Military Peter Soar introduces strategies and methods to protect GNSS positioning in a contested environment. Through specialized equipment and algorithms, Peter demonstrates how to protect position, navigation, and timing (PNT) information from jamming and spoofing. We cover more of these topics in our free book, an Introduction to GNSS: https://novatel.com/support/knowledge...
Position, Navigation and Timing (PNT) is key for GNSS positioning. Secure communications and networks derive precise time from GNSS, and trustworthy PNT is necessary for so many modern services. GNSS is the only PNT system that has 24/7 global coverage with absolute position in latitude, longitude, and height.
But the weaknesses of GNSS are that the signals are on fixed, known frequencies, and the power of signals when they reach the Earth's surface is weak. They are susceptible to being overpowered either by local interference or deliberate jamming, and to being deceived by false signals or "spoofing."
There are ways to protect your GNSS system in a contested environment. The aim is to provide actionable, reliable Position, Navigation and Timing (PNT) despite contested conditions. In Defense, we call this "Assured PNT."
To do this, we can use multi-constellation multi-frequency GNSS, encrypted signals to deal with spoofing, open-signal spoofing detection, anti-jam antennas, other sensors together with GNSS, and situation awareness.
As we explained in episode three, there are many multi-constellation, multi-frequency GNSS signals to choose from. The use of as many signals as you can access improves both accuracy and reliability. The satellites also provide encrypted GNSS signals. For government-authorized users, encrypted GNSS is used to defeat spoofing.
The antenna is the "front door" of the PNT system so we need to ensure that it is secure and only lets in the desired signals. Anti-jam antennas dynamically change the shape of the gain pattern of the antenna in response to unwanted signals. Nulls (which are areas of no signal amplification) are directed towards the interference so only genuine signals from the satellites are used.
Additional jamming signals can be excised by advanced algorithms which discriminate by frequency and angle of arrival. Beam-steering systems go further by pointing beams of increased gain towards known satellites. Both kinds of antenna protect against jamming as well as some spoofing.
At the receiver level, we can now detect spoofing so that you can take appropriate action. While jamming attempts to block your GNSS signals completely, spoofing seeks to deceive your receiver.
Spoofing is done with either rebroadcasted real signals or false signals from a simulator. For users of open-signal GNSS receivers there are emerging spoofing detection methods. Types of attacks might include matched and variable power, jamming followed by spoofing, the use of software defined radios, even spoofing before the receiver starts up. NovAtel has recently demonstrated that these attacks can be detected, allowing remedial action to be taken.
By using additional sensors that respond differently to conditions, the solution can be made to be robust as we described in Episode 5. Robustness comes from using complementary dissimilar (or "heterogeneous") sensors like GNSS+INS, which provide position and time data and rates of change, but the way that they work is different so that they are not susceptible to the same weaknesses. While each of the elements may have drawbacks, together they can provide continuous PNT data.
GNSS situation awareness is needed so that you can make informed decisions on which PNT system to rely on, and those which may succumb to attack. Modern GNSS receivers can examine and report on the signals which are inaccessible to other tools as they are below thermal noise. And, as I mentioned earlier, we can now detect spoofing with open-signal receivers. Anti-jam antennas can be used to provide information on the strength and type of jamming signals, and they can give information on the direction to the jammer.
This situation awareness enables you to make informed decisions and take appropriate action; and it is an aid to being able to attribute the interference to its source.
To protect your PNT in a contested environment, we recommend a layered defense. Select the right GNSS signals to use, and use as many as you can. If you are authorized, use encrypted GNSS signals with a secure encryption key. Employ open-signal spoofing detection, as well as an anti-jam antenna. Create a robust positioning solution with complementary heterogeneous sensors. GNSS situation awareness also helps because understanding the environment supports you in overcoming adverse conditions.
GNSS positioning and timing is achievable in a contested environment; it just requires ingenuity, suitable equipment, and the right tools.
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