Examining Cross Frequency Interference Effects in Multi-Frequency GNSS Receivers

Radiofrequency interference (RFI) can have many effects on GNSS receivers. One effect that is less commonly discussed is how RFI on one GNSS frequency band may affect a separate frequency band due to the design of its user equipment (antenna, receiver). It is useful to examine these effects to better understand actual receiver vulnerabilities. It helps with developing specifications and guidelines to limit such vulnerabilities. Furthermore, understanding and limiting these effects can help more effectively develop receiver based detect spoofing and jamming. This paper examines cross frequency effects through empirical testing of several types of GNSS antennas and receivers. Equipment ranging from consumer off the shelf (COTS) to high end survey grade were tested in an anechoic chamber with reradiated GNSS and interference signals. The system response is analyzed by looking at spectrum, automatic gain control (AGC), and carrier to noise ratio (C/No) results on multiple frequency band when there is RFI on one frequency band. The antennas tested showed different behavior with the same RFI across frequency bands. One antenna had little cross frequency effects while the other showed some noticeable effects on one band from interference on another. Different receivers also showed different responses across frequency bands with the same RFI. For example, we tested three models of dual frequency GNSS smartphone tested. One model could not utilize L5 when there was interference on L1 while other smartphones did not show this effect. This paper highlights different cross frequency effects that occur with RFI with different empirical tests. It demonstrates the importance of understanding implementation and actual performance and not just assuming each frequency band will operate independently.