GPS Receiver Failure Detection Method in High Dynamic Environment
Junyi Li,Yandong Wang, Beihang University, China
In high dynamic environment, the accuracy of GPS positioning is polluted by multiple failures. The failure types of GPS receiver in high dynamic environment are investigated in the paper, such as divergent position error and tracking loop loss caused by abnormal observation and rapid attitude change. It is common to use the Receiver Autonomous Integrity Monitor (RAIM) or Chi-Square method to detect the GPS failures. However, the detecting methods are based on some constraint conditions. For example, when the rocket spins rapidly, sometimes the number of satellites in veiw is fewer than five. In case like that, RAIM does not work. In another example, if the acceleration of the rocket is high enough, the states of Kalman filter in Chi-Square method would change fast and greatly, which increase the difficulty of distinguishing abrupt failures from normal state updating.
In the paper, Carrier phase-Doppler shift observation mutual check method and Geometric Dilution of Precision (GDOP) check method, Lock Detection are presented for detecting failures in high dynamic environment. These approaches, instead of using the residual error and innovation which are essential in the RAIM algorithm and Chi-Square method, combine the output of correlator and the carrier to noise ratio, raw observation to promote failure detection. As the rocket changes attitude rapidly, the satellites in veiw vary fast, therefore the coefficient matrix of single point positioning, which affects GDOP, reconstructs simultaneously. Furthermore, A high acceleration would cause phase lock loss, resulting in a large deviation of the correlator ouput. In order to make sure the position errors meet the requirements, GDOP is used as the detected value. Meanwhile, the correlator ouput of each channel and the carrier to noise ratio are used to detect the lock loss.
To verify the effectiveness of the proposed methods, a self-developed simulation platform covering trajectory simulator, which generates trajectory with high velocity and angular rate, and the GPS software defined receiver (SDR) is employed. These methods, including Carrier phase-Doppler shift observation mutual check method, GDOP check method, Lock Detection and Chi-Square method, RAIM, etc. are applied to detect multiple failures analyzed above on the platform. The key challenge of these methods is to set the appropriate thresholds for different detected values. For some of the detected values, like GDOP, the thresholds can be derived from the estimated variances of position errors, and others can be calculated based on the variance of the detected value and the false detecting rate.
As the result of the simulation, the performance of each method under different simulation environments is evaluated. The indexes of evaluation consist of four parts: the detected failure starting time, position error, false detecting rate and missing detecting rate. When the last two indexes fulfill the requirement,the method is better if the first two indexes are smaller. And by comparing the advantages and disadvantages of various detection methods under different anomaly circumstances, the best method is selected for the specific failure. The simulation results show the failure detection methods proposed in the paper can detect multiple failures of GPS receiver in high dynamic environment effectively.
Key words: GPS receiver, high dynamic, failure detection methods