Statistical Characterization of GNSS Signal-in- Space Ranging Errors for the User Within and Beyond Space Service Volume

The number and scope of space applications of global navigation satellite systems have grown significantly. However, the availability and the navigation performance for a spacecraft operating within and beyond the space services volume are different from those of terrestrial service volume users. To effectively evaluate the space service performance of navigation satellite systems, we present the calculation method of signal-in-space ranging error for space users. Considering the geometric visibility and the constraints of the lowest carrier-to-noise ratio, we analyze the feasibility of receiving the signal transmitted from the different off-nadir angles and obtain the coverage area of navigation satellite. Then, the relationship between the weighting factors of ephemeris errors and the orbital height of the user spacecraft is analyzed. Finally, the statistics characteristic of signal-in-space ranging error of typical navigation satellites is presented. The results show that the signal-in-space ranging error increases first and then decreases as the orbital height of the user increases. Generally, when the user's orbital height is slightly higher than the orbital height of the navigation satellite, the signal-in-space ranging error reaches a maximum. In particular, due to the significant horizontal orbit error, global signal-in-space ranging error of the Beidou geostationary orbits satellites increase significantly compared with the user located on the ground. Therefore, the impact of user height changes on the statistical properties of signal-in-space ranging error cannot be ignored when evaluating the navigation performance of the space user.