Research And Implementation Of Positioning Calculating Algorithm For BDS/GPS Software Receiver

With in-depth study of modern aerospace technology, satellite navigation technology is rapidly developed and applicated in various fields much wider and wider. BeiDou Satellite Navigation System, the Global Positioning System of United States, the Russia’s glonass System and the Galileo System of the European Union are called the world’s top four Satellite Navigation Systems.This paper researches the implementation of positioning calculating algorithm for BDS/GPS software receiver, and analyzes the simulation results on NS150BG BD/GPS experimental platform. Firstly, the nonlinear estimation and the satellite positioning technology are introduced. Then, the composition and positioning principle of the BDS/GPS system are studied. On the basis of mastering the framework of software receiver and its processing, the key process, such as the pseudorange measurement principle, the measurement error correction model and the calculation of satellite position are studied. Especially, when the visible satellites are more than four, a satellite-choosing algorithm is designed, which chooses the four satellites with the minimum geometric dilution of precision for further calculating. The positioning calculating algorithm based on the extended Kalman filter (EKF), and its simulation are conducted on the experimental platform.For comparison, the common positioning calculating algorithms, such as direct solution algorithm, Newton iterative method and least square method, are also studied. At the same time, their simulation experiments and comparative analysis are conducted. After analyzing the advantages and disadvantages of each algorithm, an improved algorithm is proposed which can be used for PVT calculating and its simulation experiment is carried out on the NS150-BG BD/GPS principle experiment platform. The proposed algorithm which fuses the direct solution algorithm, the least square method and the EKF, estimates each state error. The new algorithm utilizes the pseudorange measurement value to estimate the state of GPS receiver. The algorithm enables the least-square solver when a divergence happens in the EKF or the receiver state changes suddenly to overcome the divergency, and improve the accuracy and stability of positioning calculating. The feasibility and effectiveness of the improved method are verified by simulation results.