With the development of free space optical links (FSO) for space-ground communications comes the need to mitigate the effects of the atmospheric turbulence to guarantee a lossless connection. By having a network of addressable ground stations, we want to guarantee to always target a point where the link is available. Assuming atmospheric transmission is managed thanks to site diversity, we focus only on the influence of atmospheric turbulence on the signal injected into a single mode fiber on the downlink. The use of adaptive optics (AO) is assumed to avoid turbulence-induced signal disruptions and enable a sufficiently high level of received signal for data transmission. Up to now, AO performance adequate assessment required the knowledge of high-resolution