Abstract

To enable future space internet networks, it is needed to communicate at very high data rates between the Earth and satellites (GEO or LEO). Currently, the capacity of these links is drastically reduced due to the optical signal losses induced by atmospheric turbulence. Adaptive optics (AO) pre-compensation of the uplink beam has the potential to mitigate turbulence-induced signal losses. However, because of the point-ahead angle (PAA) separating the down and uplink optical paths, the current AO pre-compensation technique, based on the downlink beam AO correction, is suboptimal, and long and deep signal fades can still be observed, degrading the link capacity. In earlier work, we optimised the ground-to-space AO pre-compensation using an MMSE phase estimation at PAA using measurements and statistical priors of: the downlink beam phase and log-amplitude; the downlink beam phase and log-amplitude collected from several ground apertures; the downlink beam phase and log-amplitude and the phase sensed from a laser guide star at PAA. All the methods show to improve the link capacity, for various atmospheric conditions. We present a fourth MMSE estimator based on the downlink past measurements and priors. We compare the performance improvement brought by the different methods and discuss the corresponding system complexity, to identify the best performance/complexity trade-off and prepare future experimental demonstrations.