Minimum Link Distance of Terrestrial Testbeds Required to Simulate the Satellite-to-Ground FSO Communication Links

Free-space optical (FSO) communication modules to be mounted on the satellite for satellite-to-ground links need to be tested and confirmed on the ground before they are launched into space. However, it is not possible to replicate the exactly same channel conditions of the terrestrial testbed on the ground as those of satellite-to-ground FSO links. Instead, it would be possible to secure a terrestrial testbed which gives us stronger turbulent effects than the actual satellite-to-ground link. If the already implemented FSO modules perform well in the testbed, their performance in the actual satellite-to-ground link could be assured. In this paper, we estimate the minimum link distance of the terrestrial testbed required to simulate the satellite-to-ground links. For this purpose, we calculate the link distance such that the theoretical beam statistics are equal to or worse than those of actual satellite-to-ground link. For the satellite-to-ground downlink, the link distance of terrestrial testbed is determined by four beam statistics: aperture-averaged scintillation index, root-mean-square angle-of-arrival fluctuation, spatial coherence radius, and irradiance correlation width. On the other hand, the link distance for ground-to-satellite uplink is determined by the scintillation index due to small size of receiver aperture. We carry out the Monte Carlo computer simulation using the split-step method to validate the link distance of the terrestrial testbed. The results show that the testbed whose link distance is estimated by our theoretical analysis provides the worse channel conditions than the satellite-to-ground links in terms of the beam statistics.