Identifying Car Key Fobs as a Cause of Interference at GNSS Frequencies

This paper describes our methodology to investigate an unknown type of interference at the GPS L1 frequency. This interference does not cause GPS receivers to lose lock on signals and does not cause significant variations in the carrier-to-noise ratio (C/N0). However, it causes frequent false alerts in GNSS interference monitors, including in our own power-based jamming monitors that we had deployed in Virginia, North Carolina, and Colorado. We obtained data from three other independent groups in the US and Europe experiencing similar unexplained interference showing characteristic on-off keying or binary frequency-shift keying (BFSK). This paper describes how we identified their source as spurious emissions from car key fobs. Other remote-control and wireless devices used in automotive applications generate similar interference despite their specified broadcast frequency being nowhere near L1.