Modeling of Variation Characteristics of Visible LEO Satellite and Assessment of its Influence on Positioning

Low Earth Orbit (LEO) satellites have some typical characteristics, such as fast movement speed, limited coverage area, high constellation density, and so on, which will inevitably lead to frequent changes in the number and geometric distribution of visible satellites for the ground receivers. Some studies about this have been done but only focus on the coverage analysis based on complex constellition simulation or empirical equivalent modeling. Wether it can be simply and accurately modeled or not and their impact on positioning are still need more in-depth exploration. Based on the spherical distribution characteristics of satellites, this paper first derived the estimation formulas for calculating the average coverage time of satellites and the change frequency of visible satellites. Meanwhile, a modified model for the variation characteristics of visible LEO satellites is proposed. Then, we analyzed the influence of the frequent change of visible satellites on the pseudorange and Doppler positioning accuracy. Finally, to evaluate the model, a typical simulation scenario was established for the average coverage time of satellites, the change frequency of visible satellites, and the influence on the positioning accuracy factor. Results show that, the error of the proposed model is 5.23%, and the error is reduced by 76.27% compared with traditional model, which can well approximate the satellite coverage time and the change frequency of visible satellites. It is also found that under the condition of the same number of satellites, the mean and variance of the Doppler Dilution of Precision (DDOP) are 64 and 480 times of the Geometric Dilution of Precision (GDOP), respectively.