Orbit refinement for software defined radio for space applications

Digital down-conversion in software defined radios in space-to-Earth and Earth-to-space communications is challenging due to potentially large Doppler frequency offsets. The predictability of satellite orbits suggests that a computed Doppler offset could be used to perform an orbit-informed down-conversion. However, publicly available orbital parameters and orbit propagator codes lack the accuracy required for fine Doppler removal. This paper proposes a technique to adjust the orbital parameters until the computed Doppler profile matches the Doppler profile in the received signal. This technique is applied to a real signal recorded from a satellite overpass and is shown to be able to very accurately estimate frequency offsets.