Assessment of GNSS Jamming on the Border of a XXI Century Conflict
Antonia Ivan, Ileana Mihu, Alexandru Pandele, Mihnea Ion, Marius Trusculescu, Claudiu Cherciu, Romanian InSpace Engineering S.R.L. (RISE); Théotim Hentzien, IPSA
Date/Time: Thursday, Sep. 19, 1:50 p.m.
Interference and jamming are among the most serious vulnerabilities of GNSS. Unlike spoofing, which, through a variety of methods has been brought to extinction in all but the simplest and oldest of receivers, interference and jamming are directly impacting the radio-frequency spectrum on large areas, disturbing or even stopping GNSS services for multiple users. The war in Ukraine has brought to attention GNSS jamming at a scale and frequency that has not been seen before. Used as a means to deter long range maritime or aerial drone attacks, GNSS jamming has been impacting not just the conflict area, but also neighboring countries. Civilian infrastructure and operations relying on GNSS timing and/or positioning have been constantly affected by powerful jamming in the Eastern parts of Romania and in its adjacent maritime and aerial international space. Commercial planes crossing the Black Sea from Turkey reported GNSS signal loss when approaching Constanta, the most important Romanian port. The same was reported by maritime ships.
With a network of GNSS receivers deployed all over Romania and on the Black Sea shore, RISE had direct access on the status of the RF environment, prior and during the conflict in Ukraine. This allowed us to perform statistical analysis on the number and duration of events, on the central frequency and affected bandwidth, and on the impact on the signal from various constellations. As a byproduct of an experiment, RISE has collected GNSS data from a receiver onboard a stratospheric balloon, during most of its flight. This has shown high levels of GNSS jamming at high altitudes, between 9000 m and 36000 m and prompted RISE to perform a dedicated balloon experiment in May 2024.
The paper shall present the statistical assessment of the jamming events at the Black Sea, as well as a detailed analysis of the data collected during the balloon flights. The paper shall be based on datasets providing a unique perspective on the impact of large scale GNSS jamming on the border of a conflict area.
The GNSS equipment used allowed the collection of multi-frequency multi-constellation measurements, thus providing comprehensive datasets to be analyzed. As the fixed GNSS stations deployed on the Black Sea shore have been operational since November 2021, a comparison can be performed between the jamming activity before and after the start of the military conflict.
The first step of the analysis is the characterization of the detected interference events based on their central frequency, bandwidth and duration. All the stations and the stratospheric ballon are equipped with different types of Septentrio GNSS receivers, which use advanced algorithms for RF spectrum monitoring and interference detection. They provide the user with information about the radio-frequency bands where interferences have been detected. For the purpose of this analysis, an interference event has been defined as interference detected on the same central frequency, for a continuous period or with interruptions not larger than 3 seconds.
Next, their impact on the positioning solution needs to be evaluated, taking into account several factors, such as variations of the number of satellites used for positioning, variations of the C/N0 values and positioning accuracy. This allows the classification of the interference events in terms of severity and affected GNSS frequency band. The events are first characterized based on several factors, such as the event duration, the bandwidth and the central frequency of the interference. Then, the severity is assessed depending on their impact on the PVT parameters. If the impact is significant (i.e. the position accuracy is reduced or the number of satellites has a large drop), it is considered that the event has high severity. High severity events or days with a high frequency of events are subjected to an additional analysis.
A preliminary analysis of the GNSS data collected by the fixed stations located near the Eastern border of Romania revealed that jamming events have been encountered more frequently in the last two years. Several reports of loss of GPS position from civil aircraft operating at a Romanian airport near the Black Sea and by ships navigating in the coastal waters have been investigated using the collected data and interference events were discovered in the GPS L1 band, corresponding to the periods with the reported loss of position.
The investigation of these isolated events reported by civil aviation and maritime users encouraged us to perform an assessment of the collected data over a longer period. Therefore, four months of data from the beginning of 2023 were analyzed in terms of the impact of the interference events correlated with the number of satellites used in PVT. The stations providing the data are installed in different parts of Romania, near international airports, two of them being located closer to the Eastern border and one of these two being also at less than 15 km from the Black Sea coast. Over 200 events occurred at both airports, almost all of them being in the L1/E1 and L2 frequency bands and 97% of them having a duration of less than 10 seconds. The events with short durations had no significant impact on the number of satellites used for positioning, other than a few small drops. It was concluded from this analysis that the types of events which could be correlated with larger reductions in the number of satellites (sometimes reducing them to below four or even causing a loss of all satellites for a few seconds), are the continuous interference events with durations longer than two minutes, having the central frequency within the L1/E1 band, and the intermittent events with a cumulated duration longer than two minutes and with the central frequency corresponding to the GPS L1 central frequency (1575.42 MHz).
This first assessment of the detected interference from the data collected by the ground stations determined the initiative to further expand the analysis over a longer period and to more stations located near the Black Sea coast. This shall be presented in the final presentation. Moreover, it was also an inspiration for the idea of studying the jamming activity at higher altitudes through stratospheric balloons.
The stratospheric balloon was launched at the beginning of November 2023 and reached a maximum altitude of 36691 m after approximately 1h and 40 minutes of flight. A Septentrio mosaic GNSS receiver was used to collect measurements in the L1 frequency band. Interference events were detected almost throughout the flight, in the GPS L1/Galileo E1/GLONASS L1 bands. Most of the events had short durations, below 30 s, while a few of them lasted for over 1 minute. Furthermore, after the first 30 minutes of flight and at about 12000 m altitude, the number of tracked GPS and Galileo satellites started to decrease significantly. The degradations could also be observed in the C/N0 dataset, with mean values per constellation reduced from over 35 dB-Hz for GPS, 36 dB-Hz for Galileo and 38 dB-Hz for BeiDou, to about 20 dB-Hz for GPS, 26 dB-Hz for Galileo and 32 dB-Hz for BeiDou. The average number of satellites used in PVT dropped in the case of GPS from 13 to 5, for Galileo dropped from an average of 8 to 5, while for BeiDou it dropped from 16 to 12. The positioning mode switched from SBAS augmented to standalone multi-constellation. The situation further degraded when the balloon reached 26000 m, 80 minutes after the start of the flight. The average number of GPS satellites dropped further to 2, the number of Galileo satellites dropped to 3 and the number of BeiDou satellites remained between 12-13. For the few GPS and Galileo satellites still remaining in the PVT solution, the average C/N0 was above 23 dB-Hz. BeiDou further dropped to an average of 9 satellites in the PVT solution during the last 15 minutes of the flight, while the corresponding average C/N0 dropped to 29 dB-Hz.
The interesting findings of the first experiment with the ballon shall be further studied through a second ballon launch. Due to some mass constraints for the payload of the first balloon, a L1-only antenna was used for collecting the GNSS data. The second ballon shall be fitted with a triple-band antenna. The measurements rate shall also be increased from 1 to 10 Hz. Another idea to be explored is the launch of two ballons. Their measurements shall be synchronized in order to estimate the direction of the jammer.
The assessment that shall be presented in this paper exploits the large volume of data collected by fixed GNSS monitoring stations, located all around Romania, with a particular focus on the ones placed closer to the Eastern border. As more than two years of GNSS measurements are available, the impact of jamming on the local RF environment is extensively analyzed. Correlations between detected interference and degradations of the PVT parameters are made in order to determine the severity of the events.
One innovative aspect is the use of stratospheric ballons to detect jamming in the GNSS spectrum. While the results obtained with data from the ground stations are significant for terrestrial and maritime users, the extension of the study up to altitudes of about 36000 meters provide a unique perspective of the jamming activity and its impact on the PVT solution at high altitudes. Therefore, the findings can be relevant for civil aviation and military applications.
This paper shall provide valuable insights for a better understanding of the effects of GNSS jamming at different altitudes in a sensitive area close to a military conflict. The purpose of the study is to contribute to the global initiatives of increasing PNT resilience and improving the jamming detection and mitigation techniques.
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