Session B4: Spectrum: Protection and Optimization

Precise Interference Localization with Commercial GNSS Receiver Modules
Wim De Wilde, Jean-Marie Sleewaegen, Bruno Bougard, Septentrio NV
Date/Time: Thursday, Sep. 19, 4:00 p.m.

GNSS navigation is a key component in many professional applications. Availability of service is critical. GNSS is however vulnerable to interference, as it uses very weak signals. While state-of-the-art GNSS modules can mitigate structured interferences like continuous waves to a certain extent, high-entropy interference is a major concern. This type of interference overlaps both in time and in frequency with GNSS signals. ATV transmitters, overpowered GNSS reradiators and intentional broadband noise jammers are examples of high-entropy GNSS interference sources. The impact of high-entropy interference signals can be mitigated with spatial antenna techniques or with inertial navigation techniques. These methods however usually impose significant size, weight and power constraints and are often not capable to support high-precision GNSS applications while operating in an interfered environment.
Alternatively, the interference source could be localized, notified, and shut down. This would solve the root cause of the problem. A precise localization of the transmitter is desirable, ideally with an accuracy of a few tens of meters. This is a challenging requirement, particularly in situations where broadband transmissions affect GNSS operation in a perimeter of many tens of kilometers. The search process can be automated with multilateration, using a time-difference-of-arrival technique. In this approach, synchronized receiver nodes capture the timing of the interference signal. The timings are used along with the location of the receiver nodes to pinpoint the transmitter, exploiting time-of-flight physics.
In this presentation we will discuss localization results obtained with commercial multifrequency multi-constellation GNSS receiver modules. The LGA-modules used in the test have the capability to capture interference signals, synchronizing their timing with GNSS. We used timestamped signal logs obtained from two receiver modules to estimate the position of actual interference sources, which were affecting a large area. In this setup, one module was on a fixed location, while the other one was installed in a moving vehicle operating in an area affected by wideband interference. This simple setup allows operators to localize static interference sources autonomously.
After outlining the concept behind the localization algorithm, we will show results obtained during outdoor jamming tests organized in September 2023 on the island of Andøya, in the north of Norway. The organizers (Nkom, FFI, NPRA, JV, and NRS) deployed various types of jamming from a well-surveyed location, offering a perfect testbed for multilateration techniques. The environment also included various challenges, like objects acting as a reflector. Nonetheless, the obtained localization results meet the desired accuracy objective.
An important prerequisite for the operation of this technique, is that the GNSS receiver module itself is still able to keep track of its time and position. The receiver modules used in the test implemented various interference mitigation techniques, enabling them to maintain a GNSS-fix in heavily jammed environments. We will discuss their capabilities and show performance results obtained in the jamming tests discussed above.
Finally, we will discuss the impact of the geometry of the receiver nodes and the relation to covariance ellipses. We will also show that the receivers used in the experiment can support extremely large node-to-node distances, suitable to trace interference sources affecting a very large area. This is illustrated with ranging and positioning level localization results.