Complex Cross Ambiguity Function Post-Decomposition Spoofing Detection with Inverse RAIM

Abstract

In this paper, we present decomposition results of the Complex Cross Ambiguity Function (CCAF) of spoofed Global Navigation Satellite System (GNSS) signals into their constitutive components [1]. We also propose a new, post-decomposition detection algorithm based on a new "inverse" Receiver Autonomous Integrity Monitoring (RAIM) concept. The goal is to differentiate the spoofed and the authentic satellite signals to generate an authentic navigation solution. First, each satellite provides the two sets of signal parameters (code phases) post-decomposition. Using combinations of these sets, we calculate the pseudorange residuals and identify the two consistent (the authentic and spoofed) navigation solutions among all possible signal combinations over different times. The method is applicable to spoofing scenarios that can lead to Hazardous Misleading Information (HMI) and are difficult to detect by other means. The method can identify spoofing in the presence of multipath and when the spoofing signal power matches with offsets in code delay and Doppler frequency relatively close to the true signal. Spoofing can be identified at an early stage within the receiver without additional augmented sensors.