Research On Anti-jamming And Multipath Mitigation By Reduced Distributed Vector Sensor In Satellite Navigation Systems

The satellite navigation system adopting the spread spectrum technology, the satellite signal is submerged by the mechanical thermal noise when it reaches the ground. And the receiving circumstance is complicated, inducing the multipaths by reflection and diffraction. So, the satellite navigation receiver is easily interfered by the intent jamming, some electromagnetic signals used in civilian applications and multipath. The high performance satellite navigation system like Local Area Augmentation System (LAAS) and Joint Precision Approach and Landing System (JPALS) require the compensation of the measurement error induced by the Phase Center Variance (PCV) and the Group Delay (GD) after antenna array beamforming. The vector sensor element electric dipole has the stable phase characteristic, and it is prefect for the navigation measurements. The reduced distributed vector sensor constructed by the electric dipoles can form the vertical linear array and the three dimensional array, distinguish signals by polarization state and receive signals by polarization diversity. It has many advantages compared to the tranditional antenna array. In this dissertation, the high performance satellite navigation reduced distributed vector sensor anti-jamming, multipath mitigation, and the Phase Center Variance and the Group Delay calibration after beamforming are researched. The contents are as follows:(1) First the theory of the reduced distributed vector sensor is researched. The vector sensor model considering the vector sensor element patterns is deduced by using the spherical to rectangular coordinate transfer and the relationship between electric field and magnetic field. It is easy to understand. The model simulates the real measurement data, and it is the foundation of the reduced distributed vector sensor application. The direction of arrival estimation errors by the Cross Product method are presented using the three orthogonal electric fields and the three orthogonal magnetic fields measured by the three dipoles and three loops which formed the vector sensor. In war, the direction and position estimation of the jamming machine is very important. The reduced distributed vector sensor consists of two magnetic loops can be installed far away from each other compared to the half wavelength of the wave propogated, eliminating the mutual coupling. The result of the direction of arrival by vector sensor Cross Product method can choose the right peak of the Multiple Signal Classification (MUSIC) algorithm estimated, suppressing the ambiguity caused by the large array elements spacing.(2) The reduced distributed vector sensor using in anti-jamming is researched. The reduced distributed vector sensor with a three dimensional structure is presented. And the comparisons of several anti-jamming algorithms are simulated based on it. The distributed vector sensor gives out the direction of the radio frequency jamming and the polarization state of the jamming. Polarization diversity reception of the elements selected by the reduced distributed vector sensor can eliminate the vertically polarized wireless communication signals and the horizontal polarized TV broadcast signals which are orthogonally polarized compared to the receiving vector sensor elements with the same or near direction of the satellite signal, while ensuring the satellite signal receiving. On the basis of elevation and azimuth estimated, the vertical L shape sensors in the reduced distributed vector sensor depart the phase and amplitude of the vector data received to realize the signal match, then the polarization state is eatimated.(3) The reduced distributed vector sensor using in multipath mitigation is researched. The polarization state of the multipaths varies with the reflection angle, and it is not the satellite signal's right-circular polarization any more. The direction and the polarization state estimations of the arrivals by the three dimensional reduced distributed vector sensor presented in the dissertation solve the problem of the direction of arrival estimation of the correlated signals, give out the directions of arrivals and realize distinguishing the multipaths in the polarization field. The reduced distributed vector sensor multipath mitigation method researched in the dissertation solves the problem that the short delay multipath can't be eliminated in the signal processing multipath mitigation technique. The anechoic chamber test result of the circularly polarized chock ring antenna's Desired-to-Undesired Ratio (satellite signal to multipath signal ratio) which is the description of the multipath mitigation ability is also presented in the dissertation. Through comparison, it is clear that the multipath error of the pseudorange measurements is almost eliminated by the method presented in the dissertation, and it is greatly better than the chock ring antenna which is operated in most systems and the deterministic beamforming (DBF). The data received estimates the direction of the radio frequency jamming, and the carrier phase data obtained after correlation estimates the direction of the multipaths and the satellite signal. The reduced distributed vector sensor beamforming points at the desired satellite signal estimated, and places nulls at the direction of the radio frequency jamming and the multipaths estimated.(4) The calibrations of the Phase Center Variance and the Group Delay after beamforming are researched. The effect on the receiver carrier phase measurements by the Phase Center Variance and the effect on the receiver pseudorange measurements by the antenna Group Delay are presented, and the anechoic chamber test results of the Phase Center Variance and the Group Delay of the antenna are presented. The phase characteristics after beamforming by several anti-jamming algorithms are analyzed. Then the amplitude and phase modeling improved Minimum Variance Distortionless Response (MVDR) beamforming algorithm is proposed in the dissertation. By the algorithm, the non ideal antenna array beamforming points at the satellite signal and the equivalent phase center in this direction is always zero degree, and places nulls on the directions of the radio frequency jamming and multipath estimated. Calculate the Group Delay after beamforming in the direction of the satellite signal further, and the receiver pseudorange measurements error can be compensated.The reduced distributed vector sensor researched in this dissertation can provide the theory reference and the method support for the project of antenna array anti-jamming and multipath mitigation in the high performance satellite navigation system.