Research on Satellite Occurrence Probability in Earth Station's Visual Field for Mega-Constellation Systems

In this paper, we focus on the satellite occurrence probability in the earth station's visual field for mega-constellation systems. Based on the configuration of Walker constellation, we deduce the geometric relationship between the satellite phase interval and the line-of-sight angle of earth station at different elevation angles, and then analyze the law between constellation scale and line-of-sight angle of adjacent satellites. According to the given line-of-sight angle, the visual field of earth station is divided into several regions, and the satellite occurrence probability in each region can be derived. The analysis indicates that, with the expansion of the constellation scale, satellite occurrence probability in each region increases and approaches to 1. Based on the above analysis, we propose an access and handover scheme suitable for mega-constellation systems. It is assumed that the earth station is equipped with a wide shaped beam, which is pointing to a certain fixed region. There is always a visible satellite in the beam, through which the earth station connects to the constellation system and it can avoid the calculation burden of extrapolating a large number of satellite orbits. Simulation results demonstrate that the variations of space-earth link distance, radial velocity and elevation angle are extremely slight. Therefore, our proposed scheme can be well applied in the mega-constellation with frequent handovers, which can reduce the overhead of time and frequency calibration.