Research On GNSS Receiver Autonomous Integrity Monitoring

With the rapid development of global satellite navigation system (GNSS), the accuracy of GNSS positioning results is better and better, which can meet the needs of most users. In contrast, people pay more attention to the safety and reliability of the results. As one of the index of navigation performance, GNSS integrity is the ability of the system to be able to issue a warning to the user in a timely manner when the GNSS system fault appears, it becomes more and more important. Receiver autonomous integrity monitoring (RAIM) is a self-check at the user end, only depending on the received data, with fast response advantages,low cost, flexible, is currently the main research direction.RAIM is embedded inside the receiver, so the use of different positioning algorithm of the receiver corresponding to different RAIM. Most of the traditional receiver is linearized by the nonlinear observation equation of GNSS system, and the least squares (LS) solution of the linear equation is used as the positioning result. There are errors in the process of linearization,so there are both observation matrix error and observation error in GNSS observation equation, and the total least squares(TLS) model is more suitable than the least square model for GNSS observation equation. In this paper, we analyze and compare the TLS solution and LS solution, and come to conclusion: the TLS solution is more resistant to interference. This paper proposes a RAIM based on TLS method. With the rapid development of GNSS system,we should not ignore the case of multi satellite faults appear at the same time But the traditional single satellite fault exclusion algorithm is not suitable for multi satellite faults. To solve this problem, a multi satellite faults exclusion algorithm is proposed. With simulation,this algorithm can find out the fault satellite, and the algorithm is also suitable for single satellite fault conditions.The LS solution only uses the observation value of the current time, and the positioning solution obtained by the extended kalman filter (EKF) is used for the observation values of all the time, so the results are more smooth and accurate. This paper introduce a RAIM based on EKF innovation, and the algorithm is verified by simulation. The innovation-RAIM also uses only the innovation of the current time, so it can respond to the step fault quickly, but the effect is not ideal for slowly changing fault. Therefore, this paper proposes a RAIM based on EKF innovation accumulation, which is a new method to detect and exclude fault with the method of pushing forward a bit of timen from the current time and accumulate all the innovations in these moments into the current time. This paper simulated the innovation accumulation RAIM, and compares the fault detection performance both in step fault and slowly changing fault.The advances in this research can provide some reference for the development of GNSS integrity technology.