A Systematic Orbit Simulation For Spaceborne GNSS Receiver Design

Augmenting the positioning, navigation, and timing (PNT) services provided by global navigation satellite systems (GNSSs) using low-Earth orbit (LEO) satellites, known as LEO-PNT, has become a recent research focus. However, the highly dynamic LEO environment and the demand for real-time, high-precision performance present significant challenges for the design of spaceborne GNSS receivers onboard LEO-PNT satellites. To develop a comprehensive understanding of the operational scenario for spaceborne GNSS receivers, a set of systematic orbit simulations is proposed based on the General Mission Analysis Tool and MATLAB. The aim is to support geometric and link performance analyses between GNSS and LEO-PNT satellites, and to identify key factors influencing onboard GNSS receiver design, such as Doppler shift and GNSS satellite visibility. GNSS constellations, exemplar LEO-PNT satellites, and ground stations with components are modelled, providing an integrated simulation framework for the entire LEO-PNT system to facilitate design optimisation. A parametric study on Doppler shift shows that absolute Doppler shift for GNSS signals with frequencies near GPS LI most frequently occurs within 20-60 kHz, with 43-57% of values in the 20-40 kHz range and 33-43% in the 40-60 kHz range. The right ascension of the ascending node and inclination of the LEO-PNT orbit are found to have significant impacts on Doppler characteristics, with differences of up to ~ 20,000 Hz, whereas altitude has negligible effects.