| The Global Navigation Satellite System(GNSS)time service is an important means for modern society to obtain standard time.It is widely used in national major infrastructures such as finance,power,communications,and transportation to achieve precise time synchronization across a wide area.The current electromagnetic environment is becoming increasingly complex,and various interference against GNSS is emerging one after another.Spoofing has become one of the main threats to satellite navigation timing due to its strong concealment and great harm.This thesis focuses on the study of GNSS time anti-spoofing techniques.The main study contents and innovations are as follows:First,established a mathematical model of time spoofing attacks,and summarized typical time spoofing scenarios.Existing spoofing and anti-spoofing study focused on the field of navigation countermeasures;they did not systematically study the characteristics of GNSS time spoofing.This thesis establishes a mathematical model for common time spoofing techniques,analyzes the influence characteristics of different spoofing methods on timing solutions based on the model,and summarizes 10 typical time spoofing scenarios.Through the analysis of the shortcomings and applicable scenarios of the existing timing anti-spoofing techniques,the study direction of the time spoofing detection and mitigation techniques in this thesis is clarified.Second,propose a meaconing attack detection method.Study on meaconing attack that meets the consistency check.According to the feature of the deviation of the mean value of the clock bias prediction error in this scenario,a method based on the Recursive Forgetting Factor Least Squares(RFFLS)clock bias prediction meaconing detection method is proposed.Through theoretical deduction,the main factors affecting the performance of the algorithm are analyzed,and the detection effect is verified by simulating the Beidou one-way time spoofing scene.Experimental results show that when the meaconer and the receiver are in a straight distance of 244 m,for a false alarm probability of 0.15%,the detection probability of the algorithm in this thesis can reach more than 99% in a short period of time.Third,a generative spoofing detection method is proposed.The generative spoofing that meets the consistency test is studied.According to the feature that the clock bias must be abnormal in the high-order difference domain in this scenario,the clock bias is used to construct the test statistic.A generative spoofing detection method based on second-order differential accumulation of clock bias is proposed.Based on theoretical derivation and Monte Carlo simulation,the performance and parameter setting rules of the algorithm are analyzed,and the mainstream Texas Spoofing Test Battery(TEXBAT)is used for testing and verification.The results show that the algorithm in this thesis has no false alarms in the normal scenario,and the test statistics far exceed the threshold in the time-spoofing scenario,and the detection time does not exceed 10 s.Finally,an improved time spoofing mitigation algorithm is proposed.In the context of generative spoofing,the traditional time spoofing mitigation algorithm has deficiencies in the frequency drift estimation and spoofing correction mechanism,which is based on the Robust Estimator(RE).The frequency drift estimation model is established,the spoofing correction mechanism is optimized,and a time spoofing discrimination and mitigation method is proposed.A dynamic model closer to the real system is established,and the main factors affecting the performance of the algorithm are analyzed.In the experiments,the root mean square error of the clock bias of the traditional spoofing mitigation method is more than 700 m,and instability appears,while the root mean square error of the clock bias of this method is reduced to less than 107 m when there is no available satellite.When the satellite is available,it drops to less than1 m,and it has been available during the experiment.The study results of this thesis can be applied to the spoofing detection and mitigation of timing receivers,improve the user’s anti-spoofing ability,and provide an important reference for the timing security reinforcement of major infrastructure. |
