Two-ray channel models with doppler effects for LEO satellite communications

In this paper we present some two-ray models with Doppler effects for Low Earth Orbit (LEO) satellite links. We show that satellite motion-caused Doppler shifts are different along the two rays, resulting in a time-varying phase shift. This is quantified with a few Doppler models and approximations. The combined interference effects, along with the path length difference caused phase shift, are calculated using a generic LEO pass-over. Channel gains are computed and compared using various antenna patterns and system parameters. The models show good agreements except for very low elevation angles. They demonstrate that a tracking antenna is effective in reducing fading for moderate to high elevation angles. Fixed patch antennas perform well. Omnidirectional and dipole antennas perform poorly. Higher carrier frequency and higher antenna height lead to faster fades. The fading becomes deeper at low elevation angles. Very fast fading is observed near the ends of a pass-over.