Research On Key Technologies Of Interference Detection And Mitigation For GNSS Receiving System

The positioning,navigation and timing services(PNT),provided by Global Nav-igation Satellite System(GNSS),have a significant impact on all aspects of people's daily lives.In some special scenarios,such as military,rescue,civil aviation and other emergencies which may concern the safety of human lives,GNSS are required to pro-vide stable,continuous and reliable services.However,the inherent characteristics of GNSS signals,such as low received power,openness,and accurate predictability,may lead to their vulnerability to the unintentional or intentional interference.Among these interferences,narrow-band RF jamming and spoofing attack greatly reduce the perfor-mance and security of applications which rely on the GNSS services.In this paper the mechanism of narrow-band RF jamming and spoofing are analyzed in detail.Based on the key anti-interference technology of the GNSS receiving system,the anti-interference algorithms for single-antenna receiving system are sufficiently studied and compared.With the objectives of low cost,low complexity and high robustness,the following key technologies are studied:The orthogonal projection algorithms widely used in the current anti-interference field have high computational complexity.By introducing a low complexity subspace tracking algorithm,the complexity of the algorithm can be greatly reduced.For the subspace tracking algorithm FAPI,the numerical stability problem caused by the inverse square root of the matrix is found in the derivation process.An improved algorithm,MFAPI,which normalizes the subspace base matrix by matrix product,is proposed and the detailed derivation process is also presented.The numerical stability of MFAPI is guaranteed by rigorous mathematical proof.The simulation shows that the MFAPI algorithm has the fastest convergence speed while ensuring numerical stability in the low-complexity subspace tracking algorithm with current low-complexity(O(3NL)).A method based on subspace tracking algorithm for anti-narrowband RF inter-ference is proposed from the perspective of time-frequency domain.Applying MFAPI algorithm to subspace base estimation need to solve the problem of high complexity EVD for the estimation of subspace base matrix.An estimation method for the num-ber of multi-interference sources based on the statistical characteristics of GNSS satellite signals and noise is proposed.This method is superior to the estimation method based on information theory criteria.Compared with the current mainstream time-frequency domain methods,such as STFT and SPWVD,the experiments show that this method is superior to the above method in the estimation accuracy of interference signal RF spectrum,especially in low JNR scenarios.The existing spoofing detection algorithms with single estimator may lead to the inaccurate problem of detection.Meanwhile the?²fitting function,which uses code correlator?_ELcriterion to detect the spoofing,may lead to the problem of model applica-tion error and the inaccurate estimation of freedom degree.A joint detection algorithm based on signal power and W-test is proposed.The median filter is used to filter out the singular values generated by the instantaneous jump of the data.These singular values can directly cause the high false alarm probability of the W detection algorithm.For the individual power detection quantity,the selection of the decision threshold is particularly important.If the decision threshold is too low,it will lead to serious false alarm probability.If the decision threshold is too high,the low power gain spoofing signal cannot be detected,and the joint estimation with W fitting test is complemented.The detection algorithm can effectively compensate for the impact of the uncertainty of the decision threshold.Experiments show that the power and W-fitting joint test algorithm can effectively detect spoofing.The existing spoofing mitigation methods have high equipment cost and complexity.A single antenna orthogonal projection spoofing mitigation method based on MFAPI algorithm is proposed.Simulation experiments show that the estimated accuracy can reach 82%in the spoofing situation with the lowest spoofing signal power gain of 0.6d B.Experiments using the TEXBAT test data set show that the algorithm has a good spoofing mitigation effect under the minimum spoofing power gain of 1.3 d B.