Study On GNSS Spoofing Detection And Mitigation Techoniques

The satellite navigation system plays an important role in national defense and economic construction.However,the security of navigation signals is becoming more and more important with the development of satellite navigation technologies.At present,spoofing and anti-spoofing technologies attract increasing attention in the field of satellite navigation.This dissertation focuses on the research of spoofing detection,classification and mitigation of GNSS(Global Navigation Satellite System).The main work and innovative achievements of this dissertation are introduced as follows.1)For the spoofing detection using an antenna-array receivers,it is necessary to capture and track all the spoofing signals and estimate their parameters,which would result in a large amount of calculation.To solve this problem,a method based on the spatial correlation of spoofing is proposed.If spoofing signals exist or not,the distributions of cross correlation of the signals received by array elements are different,and this can be used for spoofing detection.The method can be used to suppress the acquisition and tracking of the signals and reduce the amount of calculation.For the direct-retransmit spoofing,this method has good detection performance.If the power of each spoofing signal is 3d B higher than that of the authentic signal,the detection probability of this method can reach more than 99% within 0.1% false alarm probability.For the separate-retransmit spoofing or a generator,the performance of spoofing detection is related to the number of the spoofing signals.If 4 spoofing signals are transmitted,it can reach more than 90% detection probability within 0.1% false alarm probability when the power of each spoofing signal is 6d B or 12 d B higher than that of authentic signal.2)It is difficult for spoofing classification,if a single-antenna receiver was used to obtain the spatial characteristics of spoofing.And long moving distance and long detection time is needed,if the spoofing classification method which based on the traditional synthetic antenna array was used.In order to solve these problems,a spoofing classification method based on the directivity of antenna is proposed.Because all spoofing signals have a same angle of arrival to the receiving antenna,the gain of spoofing signals would change similarly when the antenna rotated.Consequently,the carrier-to-noise ratios of the spoofing signals with different PRN(Pseudo Random Noise)code would change similarly.Then the correlation of the changes in the carrier-to-noise ratios can be used to identify the spoofing.Using this method,the moving distance of the receiver can be reduced and the detection time could be shortened correspondingly.The simulation results show that the method can effectively identify the spoofing signals transmitted by the same antenna,and the detection probability can reach about 99% within 1% false alarm probability.3)For the traditional spatial spoofing mitigation methods,the calculation of correlation matrix and inverse matrix of the signals is inevitable,and the amount of this calculation is relatively large.In order to solve this problem,a spoofing mitigation method based on signal phase compensation and signal cancellation is proposed.Before signals dispreading,the cross correlation of signals between two antennas is used to estimate the phase difference of spoofing.In order to cancel the spoofing signals,the signals received by two antennas are reversely added after phase compensation.The simulation results show that the proposed spoofing cancellation method has good performance.The spoofing mitigation performance of this method for a 4-element antenna array is about 2d B higher than that of the traditional subspace projection method.And the gain of the authentic signal is reduced about 1.6d B compared with the traditional method.4)Aiming at the problem that the spoofing mitigation performance of current spoofing mitigation methods deteriorates when a jamming exists,a joint mitigation method for spoofing and jamming is proposed.A two-stage filter structure is used in this method.At the first stage filter,the weight calculation and the signal weighting are carried on taking each channel as the reference,and multiplexed output are obtained.Furthermore,the spatial information of the spoofing and authentic signals is preserved while the jamming suppressed.At the second stage filter,the output signals are used for parameter estimation,signal despreading,spoofing recognition and mitigation.At the same time,a beam can be formed in the direction of the authentic signal to improve its power.The simulation results of a 4-element antenna array show that the method can suppress the spoofing in a wide range of spoofing power,whether a jamming exists or not.And the method can enhance the power of authentic signals.If there is no jamming,the array gain can reach 4d B ? 5d B in the direction of authentic signals.And If a jamming exists,the jamming and spoofing can be mitigated simultaneously,and the power of authentic signal can be increased by about 2dB.