Variation analysis of satellite navigation message and its application to anti-spoofing

Global Navigation Satellite System (GNSS) is widely applied to our daily life with its stable service. The GNSS control segment routinely generates navigation message based on a prediction model and the measurements from global monitor stations. Navigation message includes each satellite's clock correction, ephemeris, and almanac which are stable and change by certain rules. The paper analyzes these parameters of Global Positioning System (GPS) and BeiDou System (BDS). Based on different changing rules of parameters, the paper divides all parameters into four categories and briefly discusses their applications in anomaly detection and anti-spoofing. Further, the computed satellite position deviations by ephemerides and almanacs of different time are researched and relevant mathematical model is established. Also, the computed clock deviations are discussed. With the increasing use of GNSS, its vulnerability has caused much concern. In general, there are many spoofing methods. In order to deceive a victim receiver to a predetermined position or time, some spoofers may change navigation message. The above analysis results can be applied to check such spoofing attacks. So two threshold models are established and their advantages and disadvantages are discussed. Combining two threshold models, the paper proposes a method to effectively utilize navigation message for anti-spoofing. Finally, the method is implemented on GPS/BDS receivers and the relevant experimental results show that it is feasible and effective in different deception scenarios where navigation message is tampered.