GPS-dependent positioning, navigation, and timing synchronization procedures have a significant impact on everyday life. Therefore, such a widely used system increasingly becomes an attractive target for illicit exploitation by terrorists and hackers for various motives. As such, spoofing and antispoofing algorithms have become an important research topic within the GPS discipline. This paper will provide a review of recent research in the field of GPS spoofing/anti-spoofing. The vulnerability of GPS to a spoofing attack will be investigated and then different spoofing generation techniques will be discussed. After introducing spoofing signal model, a brief review of recently proposed anti-spoofing techniques and their performance in terms of spoofing detection and spoofing mitigation will be provided. Limitations of anti-spoofing algorithms will be discussed and some methods will be introduced to ameliorate these limitations. In addition, testing the spoofing/anti-spoofing methods is a challenging topic that encounters some limitations due to stringent emission regulations. This paper will also provide a review of different test scenarios that have been adopted for testing anti-spoofing techniques. 1. Introduction GPS-dependent systems are ubiquitous in current positioning and navigation applications. There is an ever-increasing attention to safe and secure GPS applications such as air, marine, and ground transportations, police and rescue services, telecommunication systems, mobile phone location, and tracking the criminal offenders. Nowadays, most mobile phones as well as vehicles are equipped with positioning and navigation systems utilizing GPS. In addition, countless time tagging and synchronization systems in the telecom and electrical power grid industries rely primarily on GPS. As a consequence, such a widely used system is becoming an increasingly attractive target for illicit disruption by terrorists and hackers. GPS signals are vulnerable to in-band interferences because of being extremely weak broadcasted signals over wireless channels. Therefore, even a low-power interference can easily jam or spoof GPS receivers within a radius of several kilometres. In addition, GPS is a backward compatible technology whose signal structure is in the public domain [1]. This makes GPS technology more susceptible to disruptive interfering methods. For example, spoofing attack could effectively mislead an activity monitoring GPS receiver mounted on a cargo transport or fishing vessel. Therefore, the GPS receiver will be logging a counterfeit trajectory with
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