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Session F3b: GNSS Robustness to Vulnerabilities 1

GNSS Interference Monitoring and Detection Based on the Swedish CORS Network SWEPOS
Kibrom Ebuy Abraha, Anders Frisk, Peter Wiklund, Lantmäteriet, the Swedish mapping, cadastral and land registration authority
Date/Time: Thursday, Sep. 19, 11:03 a.m.

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The increase in GNSS interference poses a significant risk to both GNSS systems and their dependent infrastructure. Interference monitoring and mitigation efforts are critical to protecting these assets against emerging threats. This study highlights the potential of existing infrastructures, such as the Swedish CORS network SWEPOS, to autonomously detect GNSS signal disturbances.
The interference threats have led to a growing interest in GNSS development and interference detection studies for continuous monitoring of GNSS frequency bands. The general purpose of this development is to protect critical GNSS infrastructure from emerging intentional or unintentional threats. The same GNSS infrastructure can also be used for situational awareness of threat signals.
This work introduces an automated GNSS interference detection system using SWEPOS. SWEPOS, established in the 1990s, has developed in terms of network structure and modernization. It now has nearly 500 stations spread over 10–70 km, equipped with the latest receivers to track all GNSS signals. The SWEPOS Network-RTK service provides high-precision real-time correction service with nearly 10,000 users. SWEPOS ensures quality and continuity of its service by continuously monitoring data quality in real-time, near-real-time and post-processing modes. The interference detection presented in this study is part of this effort and is a near-real-time monitoring of data quality using hourly RINEX data.
The interference detection system is based on hourly RINEX data from the entire SWEPOS network and makes use of signal-to-noise ratio (SNR); it monitors for unexpected changes in the SNR values and characterizes how these changes correlate between satellites tracked at the same time. It has been shown that the method can detect and is sensitive to different types of interference and also capable of distinguishing unexpected SNR changes due to other factors, such as tree leaf attenuation, from RFI-related SNR changes. The disturbance detection system monitors the entire SWEPOS network in near real time, and it produces a signal disturbance status map and sends e-mail alerts if signal disturbances are detected.
The effectiveness of the detection system is assessed through simulations of signal disturbance waves and actual disturbance events, demonstrating its ability to detect GNSS signal disturbances. In a related study in which the author also participated, which evaluated the potential of using SWEPOS for interference monitoring and detection, four different interference waveforms centered on GPS L1 (1575.42 MHz) were simulated and GNSS receivers were exposed to these waveforms under controlled conditions. The simulated disturbance included additive white Gaussian noise (AWGN) with bandwidths of 20 MHz and 2 MHz, an unmodulated continuous wave (CW) carrier, and a frequency modulated (FM) wave. The data with these simulated interference waves was used to validate the detection system's effectiveness and it showed that the detection system is very sensitive to different types of interference waves and can detect different interference sources. The effectiveness of the detection system is also evaluated with actual interference scenarios. The system has detected several disturbances since it was established, and some examples will be presented.
The purpose of building a SWEPOS-based GNSS interference monitoring system is to provide comprehensive interference situational awareness for the entire reference network. Situational awareness is the first and critical step in risk management, such as locating, mitigating, and limiting sources of disturbance. This will play an important role in ensuring quality, continuity, and integrity of service, benefiting future critical applications and society by providing a clean GNSS spectrum.

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