  Recent advances have shown that satellite communication (SatCom) will be an
important enabler for next generation terrestrial networks as it can provide
numerous advantages, including global coverage, high speed connectivity,
reliability, and instant deployment. An ideal alternative for radio frequency
(RF) satellites is its free-space optical (FSO) counterpart. FSO or laser
SatCom can mitigate the problems occurring in RF SatCom, while providing
important advantages, including reduced mass, lower consumption, better
throughput, and lower costs. Furthermore, laser SatCom is inherently resistant
to jamming, interception, and interference. Owing to these benefits, this paper
focuses on downlink laser SatCom, where the best ground station (GS) is
selected among numerous candidates to provide reliable connectivity and maximum
site diversity. To quantify the performance of the proposed scheme, we derive
closed-form outage probability and ergodic capacity expressions for two
different practical GS deployment scenarios. Furthermore, asymptotic analysis
is conducted to obtain the overall site diversity gain, and aperture averaging
is studied to illustrate the impact of aperture diameter on the overall
performance. Finally, important design guidelines that can be useful in the
design of practical laser SatComs are outlined.
