Study On Wide Area Differential Correction Technology Based On Wide Area Augmentation System

Wide area augmentation system is comprised of a large area of the base stations, the central station and the GEO satellite and it deals with the error sources encountered in the GNSS positioning satellite. Furthermore, it models separately for each kind of error sources and generates the differential correction value. High accuracy and positioning services could be obtained by using the GNSS navigation signal and the wide area differential correction value to improve positioning calculation.In recent years, with the operation of COMPASS and the continuous improvement of GALILEO, the wide area augmentation system does not just need to improve navigation accuracy and integrity, but also provide support for multi-mode GNSS systems. Based on the Wide Area Augmentation System, the research of this thesis is about two aspects : the wide area differential correct algorithm and the system performance. This thesis establishes a Chinese region ionospheric grid model and calculates the ionospheric delay changing rate. On the above basis, this thesis proposes an improved Hatch filter algorithm which takes the ionospheric delay changing rate and observation noise into consideration. With this algorithm, this thesis calculates the carrier phase smoothing pseudorange, analyzes the Chinese region GDOP and UDRE. This thesis includes the following aspects:1. This thesis introduces the fundamentals of Wide Area Augmentation System and establishes the Chinese region ionospheric grid model at the longitude 2.5° and the latitude 5°. According to ionosphere data provided by the China Crustal Movement Monitoring Network, this thesis calculates and simulates total electron amounts of Chinese region ionospheric layer within a single day.2. This thesis analyzes the wide area differential correct algorithm. In order to solve the problem concerning the carrier phase smoothed pseudorange, this thesis proposes a method which takes into consideration of the ionospheric delay changing rate, the satellite elevation angle and the observation noise and uses it to solve the optimal smoothed time of the Hatch filter algorithm. After that, the modified method is used to implement the carrier phase smooth on the Pseudorange. The simulations show that the performance of the modified Hatch filter algorithm is better than that of the classical Hatch filter algorithm.3. Based on the LU decomposition this thesis obtains the method to solve the multi-constellation DOP and then simulates satellites quantities that are visible and DOP in the area of Chengdu and China region, under the single-constellation and multiconstellation scenarios. By the comparison of GDOP and PDOP, the validity of the LU decomposition is established. We also calculate the UDRE by the worst user location information that could be derived from a new geometry method proposed in this thesis. The comparison between the decomposition algorithm and the exhaustive grid search method is done by simulations and the results show that the decomposition algorithm achieves higher efficiency under the same constraint of accuracy.