GNSS Signal Processing under Spoofing

Radio Frequency Interference (RFI such as jamming and spoofing, represents a growing threat to GNSS receivers, especially in civil aviation, which requires a high level of accuracy, integrity, continuity, and availability. Although jamming and spoofing interference signal models have been extensively studied in the literature, and GNSS observables are commonly used in spoofing detection, the exact impact of spoofing on these observables remains relatively unexplored. Understanding the impact of jamming and spoofing on GNSS receivers is essential for enhancing their resilience and facilitating the development of more sophisticated detection methods. Developing a model of the receiver?s signal processing under jamming and spoofing conditions could enable the characterization and bounding of the impact of these threats on GNSS receivers. Furthermore, such a model would help identify different jamming and spoofing threats based on the interplay between the receiver, satellite, and spoofer geometries, as well as the receiver’s configuration. To this end, this thesis aims to characterize the impact of RFI on GNSS receiver signal processing both before and after correlation. First, this thesis investigates the impact of chirp jamming and spoofing interference on the Intermediate Frequency (IF) signal and Automatic Gain Control (AGC). Prior to correlation, the spoofing signal acts as a jamming signal for the receiver, beginning to impact the receiver at a power level comparable to the noise floor. The spoofing impact on AGC fluctuates by several decibels depending on the spoofing parameters, but tends to approximate a Gaussian process as the number of interfering signals increases. Next, the thesis characterizes the impact of spoofing on GNSS receivers after correlation by modeling the correlator output, tracking loop behavior, and C/N0 estimator under spoofing interference. The spoofing impact after correlation can be categorized into four distinct situations: nominal, induced-jamming, induced-spoofing, and induced-multipath. This study reveals complex and potentially harmful distortions, particularly in the induced-multipath situation, where the receivers encounter very significant and unpredictable distortion. This includes significant C/N0 distortions along with non-linear and chaotic behaviors in tracking loops, inducing potential loss-of-lock, synchronization bifurcation, cycle slips, and high tracking errors.