Research On Positioning Algorithms In Pseudolite Network

The Beidou System(BDS) is an all-weather, round-the-clock, satellite-based navigation system developed by our country. Similar to other Global Navigation Satellite Systems(GNSS), BDS is obviously the most effective method to get position message whether on land, at sea, in the air and even in space. However, in indoor, city canyon, tunnel where the satellite signals may be obstructed, the positioning requirements cannot be satisfied. Pseudolite technology can be used as the augmentation system for BDS as it can not only offer the extra positioning signal but also be applied independently when all the BDS signals are unavailable. Morever, with the application of carrier phase measurement,the BDS pseudolite positioning can accomplish precise point positioning with the level of centimeter. To track the advanced technology in the field of pseudolite at home and abroad and integrate it with the BDS, the main contents of this thesis include:Firstly, in this thesis, the research status of pseudolite positioning both at home and abroad is analyzed and summarized. The principle and key issues including time synchronization, ambiguity resolution, nonlinear filtering and pseudolite configuration pseudolite system are analyzed. Meanwhile, the signal structure and navigation message are designed.Secondly, the influence of the pseudolite geometry on the positioning performance is analyzed, and the DOP(Dilution of Positioning) is used to evaluate the geometric structure.The principle of the pseudolite enhancement to the Beidou is analyzed theoretically, and the simulation analysis of the precision factor is carried out according to the Beidou satellite almanac data.Besides, the influence of near-far effect and multipath effect on the location of pseudo-satellite layout is discussed. Considering these influencing factors, an adaptive genetic algorithm combining penalty factor is proposed in the case of pseudolite application of layout optimization. The results show that the method can complete the optimization of pseudolite layout under the condition of multiple restraints, in which the adaptive genetic algorithm has the advantage on convergence speed.Finally, the effects of linearization error both on the Beidou system and the pseudolite system are compared, the performance of extended Kalman filter, second-order extended Kalman filter and unscented Kalman filter are simulated and analyzed in the two system respectively. The results show that the UKF can provide better positioning accuracy when the pseudolite is closer to the receiver or the layout of pseudolites is not well optimized.However, EKF, EKF-2, UKF have approximate positioning accuracy when positioning constellations are far from the receiver as in the scene of BDS.