Investigations into Observed Anomalous GNSS Receiver Behaviour when Subjected to Adjacent Band Noise

Guy Buesnel, Mark Hunter, and Charlotte Perry

Abstract:	This paper will examine anomalous behaviour that has been observed in user equipment when subject to Adjacent Band Interference. Results of Adjacent Band Interference tests using the 1-dB C/N0 metric and other observables such as positional accuracy and time to first fix, will be presented and the authors will discuss the behaviour observed in a selection of receivers along with the possible causes of it. The authors will use a highly automated test bench to perform a series of repeated tests in order to obtain a statistically valid set of results. The use of a highly automated test bench for conducting these experiments will be introduced along with a description of the test set-up and any constraints when compared to carrying out traditional manual testing. A discussion of the efficiency improvements achieved by the use of an automated test bench will also be included. The authors will present an overview of the GNSS interference landscape with focus on the potential (well known) and increasing threat from interference in adjacent bands. Much testing has been conducted on GNSS receivers to assess their vulnerability to adjacent band interference, but several researchers have observed anomalous behaviour under certain circumstances. This observed anomalous behaviour has included reduced Time To First Fix whilst the receiver has been subject to interference, seemingly improved positional accuracy and invariant C/N0 readings. The authors will present more evidence that of the measurable metrics available from GNSS devices, C/N0 is the most appropriate for understanding the robustness of receivers to Adjacent Band Noise. One of the reasons for adopting the 1-dB C/N0 metric is that it should protect the ranging accuracy of GNSS receivers. The results that authors present will compare ranging accuracy, Time to First Fix performance and C/N0 degradation at various interference levels to understand receiver behaviour. The authors will discuss the implications of the test results on GNSS receivers designed for specific applications – this will include an overview of their main requirements and an assessment of the quantity and levels of interference they might experience in the event of LTE transmitter deployment. The paper will contain a discussion on generating realistic simulation scenarios for a Radio Frequency Constellation Simulator that could be used to evaluate receiver behaviour and highlight issues in a laboratory environment. Finally, the authors will present their views on how standards encompassing resilience for GNSS products should be developed. They will argue that OEM standards are not the most effective way to deal with the issues around GNSS vulnerabilities, especially given that threat vectors are evolving rapidly and require counter-measures to be introduced in a timely manner.
Published in:	Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018) September 24 - 28, 2018 Hyatt Regency Miami Miami, Florida
Pages:	1369 - 1388
Cite this article:	Buesnel, Guy, Hunter, Mark, Perry, Charlotte, "Investigations into Observed Anomalous GNSS Receiver Behaviour when Subjected to Adjacent Band Noise," Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018), Miami, Florida, September 2018, pp. 1369-1388. https://doi.org/10.33012/2018.16009
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