Key Techniques On Gun-borne GNSS Receiver Of The Magnetic Sensor Assistance

In order to adapt the needs of high-tech local war,precision-guided artillery shells which uses GNSS to guide has become one of the important equipment for the development of many countries.Enhanced GNSS signal capture capability and improved signal acquisition accuracy are important targets for GNSS guidance.According to the Doppler frequency shift and phase shift caused by the missile body which has short flight time and high-speed rotation,this paper uses the magnetic sensor to measure the attitude of the missile body and combines with ballistic characteristics to assist the missile-borne GNSS receiver to capture and track signal.At the same time,we also studied the method to improve the signal acquisition accuracy.Studying the characteristics of BOC modulation used in modern GNSS.The phenomenon of the acquisition ambiguity is generated according to the autocorrelation function of the BOC signal.We use the autocorrelation side lobe elimination algorithm,the filtered algorithm and none-ambiguity algorithm respectively remove the correlation between the secondary peak and the main peak thereby reducing the ambiguity of the capture.The algorithm provides theoretical basis for the research of the Algorithm to Improve the Accuracy of Acquisition and the research of the Influence of high-speed rotation of projectile on signal received by missile body.The method of improving the signal-to-noise ratio and the acquisition precision in the Intermediate frequency signal stage and the acquisition stage are studied.Intermediate frequency signal uses two-channel quadrature sampling while using IQ two branches of the signal as a data source processing.So the signal-related peaks were significantly increased.The algorithm of FPGA implementation of dual-channel despreading is deduced.Coarse acquisition of the satellite signal has a greater error.Aiming at the multi-peak structure of BOC signal,we use the least squares method and cubic spline interpolation method to estimate the code phase of the correlation peak accurately after suggesting to eliminate the side lobe effect of BOC signal correlation function by using ASPeCT algorithm.Through simulation experiments,we verify the code phase estimation error of two algorithms.Based on the characters of missile-born receiver with short flight time and high-speed rotating projectile,the method of measuring projectiles attitude by magnetic sensors to compensating for Doppler shift and phase shift is researched,which can improve signal acquisition and tracking performance.According to the characters of projectile ballistics,the expressions of frequency shift and phase shift caused by high-speed rotating projectile are derived.The measurement model of geomagnetic vector in projectile coordinate is built,then the relational expression of output value by magnetic sensors and projectiles attitude is derived.Based on the question of big error caused by using extremum ratio method to calculating projectiles pitching angles under the random noise disturbance,the integral ratio method is proposed to calculating pitching angles,then according to the character of magnetic field data,the integral model of integral ratio method is built,and then the expression of pitching angles is derived and the computational steps of integral ratio method are given,finally,the validity and rationality of the integral ratio method under the random disturbance are verified by simulation experiments.In the case of magnetic field changes,the dynamic real-time compensation of magnetic sensors algorithm is proposed.First,the ellipsoid measurement model with compensation of the geomagnetic field is built.The Newton iterative method is used to linearizing the quadratic function of measurement model.Then the measurement matrix of compensation parameters is derived.And then the least square method and total least square method are used to estimating compensation parameters.Finally,the algorithm performance is verified by using static simulation experiment and dynamic simulation experiment,the validity of compensation algorithm and compensation precision are verified by static simulation experiment verify,the validity of dynamic compensation algorithm which the compensation parameters real-time updates are verified by Dynamic simulation experiment under the condition of Environmental magnetic field change.In order to improve the accuracy of projectiles attitude measurement,the EKF algorithm and CKF algorithm are used to estimate projectiles attitude.A nonlinear Kalman filter is designed for the measurement of projectiles attitude,and the measurement of two non orthogonal magnetic sensors is the observation of nonlinear Kalman filter;Step EKF algorithm and CKF algorithm are given;According to the initial error is too large to cause the nonlinear Kalman filter divergence problem,obtain the initial attitude by using the integral ratio method as the initial value of Kalman filter state vector.The theoretical derivation and simulation experiment show that the Doppler shift and phase shift can effectively compensate by measuring projectiles attitude.The variance of calculation error of pitch angle obtained by utilizing the integral ratio method is one order of magnitude smaller than that obtained by utilizing the extremum ratio method under the condition of random disturbance.The measurement precision of projectiles attitude by magnetic sensor in the actual environment is improved.By using the integral ratio method,the initial value of projectiles attitude is obtained as the initial value of the state vector of the Kalman filter,then the EKF algorithm and CKF algorithm are estimated to further improve the accuracy of projectiles attitude measurement.The projectiles can real-time compensate the magnetic field change when high-speed spin by building the ellipsoid measurement model and using total least square method,and the adaptability of missile-born receiver is improved.