The Improved Research Of RAIM Algorithm Under Harsh Conditions

With the continuous development and widely application of the global satellite navigation system, the issue of the autonomous integrity monitoring of the receiver is given more and more attention, especially in the field of life safety(such as aerospace). Autonomous Integrity Monitoring Receiver(RAIM) achieves the satellite fault detection and fault identification using the redundancy information in the user's receiver, or other auxiliary information on the aircraft. So in order to meet the requirements of integrity performance, the special satellite enhanced system or receiver autonomous integrity monitoring(RAIM) of user terminal can be used. RAIM algorithm is currently considered to be effective, the core is to use the redundancy information of satellites in global navigation satellite system(Navigation Satellite System Global(GNSS), to achieve the purpose of multi navigation solutions for the consistency test, so as to achieve the purpose of Integrity Monitoring. However, the redundancy observations is needed in operation, integrity monitoring cannot be performed when lack visible stars. When the Satellite navigation system can no longer navigate due to adverse factors such as the bad weather or bad environment, the receiver will find the fault and promptly issue a warning to users. If the system does not have this capability or its performance is in bad state, it may result in significant security incidents, so the integrity of the system must be guaranteed. The external auxiliary systems can provide redundant information, and the most commonly used system is called the inertial navigation system(INS), when RAIM gets no extra satellite observations, INS can ensure continuous operation of the client system.The article describes the development of Receiver Autonomous Integrity Monitoring of the satellite navigation systems under the background of GNSS satellite navigation system. In harsh conditions, the user's positioning and the use of RAIM algorithm can effectively carried out in the case of satellite measurements less by increasing auxiliary information of the elevation and clock offset. Due to the rough features of the original auxiliary information, results of positioning receiver have large deviation and the fault detection and troubleshooting should be applied under the condition that the pseudorange deviation is large. In order to improve the accuracy of ancillary information, reduce the pseudorange deviation of fault detection rate and fault recognition rate in harsh conditions, the paper proposes an improved method for RAIM algorithm under the harsh conditions. The main improvement is the application of the principle of the speed with doppler, calculating the speed and clock drift which is the change rate of height and the change rate of the user's clock error. The forecast of elevation and clock error is smoothed to achieve optimal effect by the principle of pseudorange assisted by carrier phase, then adjusting parameters of the smoother to form a feedback loop by using the formed feedback of RAIM fault detection. The simulation proves the availability of this method, as well as the improvement of the positioning accuracy and fault detection rate and fault recognition rate. The application of the method on the navigation receiver plate also proves its feasibility in practical applications. But at the same time the method exposes the weaknesses, the increased computational burden makes a great influence on the process of the adjusting the receiver clock error. Therefore, there are still many areas needed to be improved.