Uncovering Subtle GNSS Spoofing by Decomposing the Complex Cross-Ambiguity Function

In this paper, we introduce a method to uncover Global Navigation Satellite System (GNSS) spoofing by directly decomposing the Complex Cross Ambiguity Function (CCAF) into its authentic and counterfeit components. We demonstrate the importance of using complex cross ambiguity measurements compared to the magnitude-only approaches utilized in prior work on spoofing detection. We also introduce a CCAF error decorrelation method to mitigate the influence of thermal noise. The detector can identify spoofing in the presence of multipath and when the spoofing signal is power-matched with offsets in code delay and Doppler frequency that are close to the authentic signal