Clock Drift Monitoring to Discriminate GNSS Signal after Prolonged Signal Loss

Global Navigation Satellite Systems (GNSS) are increasingly being threatened for military reasons, strategic purposes, or simply because of advances in consumer technology by individuals who seek to disrupt the system for entertainment. Attacks on these systems have existed since the first satellite navigation system, GPS, was implemented. Among the possible attacks, the spoofing attack is one of the most harmful and easiest to execute. The literature contains numerous approaches to detecting this type of attack. There are also many papers explaining the different possible attacks in detail. However, devices such as smartphones, which are frequently used for positioning services, verify the integrity of the GNSS signal using external data sources, such as the network data to which the phone is connected. If this network becomes unstable or the smartphone disconnects for a while, the GNSS system becomes vulnerable to certain integrity attacks. For this reason, we analyze the possibility of network connection loss and examine one specific use case, how the clock drift method, a well-studied method in the literature, can differentiate between a legitimate and a falsified signal after a prolonged signal loss, all using exclusively GNSS data retrieved from the smartphone, more specifically Android OS.