Effects of Optimized Mitigation Techniques for Swept-frequency Jammers on Tracking Loops

The presence of Radio-Frequency Interference (RFI) to Global Navigation Satellite System (GNSS) signals could bring severe threats to GNSS dependent applications and demands for effective countermeasures. Among the typical sources of anthropogenic interferers, the swept-frequency jammers are characterized by generating overpower signals with carrier frequency varying over GNSS signal bands, thus leading to disruptive effects on GNSS receiver performance. In order to counteract such types of jamming signals, the well-known Adaptive Notch Filter (ANF) is particularly appealing due to its low complexity and low computational load. Nevertheless, the residual contribution of the jamming signal after the mitigation and the presence of the ANF itself might introduce a vestigial signal distortion which is significant for high accuracy positioning. This paper presents the analysis at the tracking stage of a GNSS receiver equipped with an ANF in case of swept-frequency (chirp) jamming signals, assessing the distortion in terms of bias and shape deformation of the Delay Lock Loop (DLL) discrimination function, and using the Interference Error Envelope (IEE) and code jitter as key metrics.