Using the Swedish CORS Network SWEPOS for GNSS Interference Detection

Abstract

GNSS (Global Navigation Satellite Systems) interference detection using data from the Swedish CORS (Continuously Operating Reference Stations) network SWEPOS has been investigated. Actual interference events have been detected at these three operative SWEPOS stations using a reference interference detection system named RF Oculus developed by the Swedish Defence Research Agency (FOI). RF Oculus monitors e.g. the received power in the L1 frequency band and detects interference if it exceeds a preset threshold above the ambient noise level. Interference detection, using data from the SWEPOS network, was also performed at these three locations by investigating when the mean carrier-to-noise-density ratio of the tracked GPS L1 C/A-signals was below a determined expected level based on historical data. In total around 50 interference events were detected by the reference systems across the three locations during a period of a couple of months. Different types of interference were identified to affect the mean carrier-to-noise-density ratio from the SWEPOS receivers. This showed that detection of different type of interference is possible using SWEPOS data. Interference with durations as short as below a second were detected. Results from the reference interference detection system and detections based on data from the SWEPOS network showed that most interference events were detected by both approaches. Differences in start time and duration of detected interference events between the two methods can probably be attributed to differences in thresholds and detection methods. On the whole it is shown that the detection approach using the SWEPOS network can provide useful and valid detections.