 signals can be excised by advanced algorithms which discriminate by frequency as well angle of arrival. Beam-steering systems go further by pointing beams of increased gain towards known satellites; this needs knowledge of the satellite positions, and position and heading of the receiver; so it's a complex approach that needs extra hardware and different algorithms and software.
Both kinds of antenna protect against jamming; they also defeat some spoofing if the receiver is already tracking.
Spoofing Detection Algorithms
At the receiver level, we can now detect spoofing so that you can take appropriate action. Recall Episode Two when we explained the difference between jamming and spoofing. 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. Knowing that you are under a spoofing attack means that you can take steps to use alternative measures and use the GNSS information wisely. 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.
Using Additional Sensors for a Robust Solution
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 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.
The classic way is GNSS+INS. It is best to use tight coupling techniques that make best use of the advantages of the sensors. The algorithms in the GNSS receiver are aided by the INS so that the system gives a solution, even when fewer satellites are visible than are normally needed.
More sensors, such as visual techniques, RADAR, LiDAR and many others can be used; and, with advanced algorithms, sensor fusion can provide a comprehensively robust system.
Building Situation Awareness
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.
A Layered Defense
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. And, GNSS situation awareness also helps because understanding the environment supports you in overcoming adverse conditions.
GNSS positioning and timing is truly achievable in a contested environment; it just requires ingenuity, suitable equipment, and the right tools.
Hexagon | NovAtel Director of Marketing Neil Gerein explains how GNSS is used to solve different positioning problems in different industries. Focusing on the agriculture, automotive, and defense industries, he outlines how GNSS and its related technologies offers comprehensive solutions to deliver positioning and autonomy – assured.
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