  The utilization of extremely high frequency (EHF) bands can achieve very high
throughput in satellite networks (SatNets). Nevertheless, the severe rain
attenuation at EHF bands imposes strict limitations on the system availability.
Smart gateway diversity (SGD) is considered indispensable in order to guarantee
the required availability with reasonable cost. In this context, we examine a
load-sharing SGD (LS-SGD) architecture, which has been recently proposed in the
literature. For this diversity scheme, we define the system outage probability
(SOP) using a rigorous probabilistic analysis based on the Poisson binomial
distribution (PBD), and taking into consideration the traffic demand as well as
the gateway (GW) capacity. Furthermore, we provide several methods for the
exact and approximate calculation of SOP. As concerns the exact computation of
SOP, a closed-form expression and an efficient algorithm based on a recursive
formula are given, both with quadratic worst-case complexity in the number of
GWs. Finally, the proposed approximation methods include well-known probability
distributions (binomial, Poisson, normal) and a Chernoff bound. According to
the numerical results, binomial and Poisson distributions are by far the most
accurate approximation methods.
