  The mixed radio frequency (RF)/free-space optical (FSO) relaying is a
promising technology for coverage improvement, while there lacks unified
expressions to describe its performance. In this paper, a unified performance
analysis framework of a dual-hop relay system over asymmetric RF/FSO links is
presented. More specifically, we consider the RF link follows generalized
$\kappa$-$\mu$ or $\eta$-$\mu$ distributions, while the FSO link experiences
the gamma-gamma distribution, respectively. Novel analytical expressions of the
probability density function and cumulative distribution function are derived.
We then capitalize on these results to provide new exact analytical expressions
of the outage probability and bit error rate (BER). Furthermore, the outage
probability for high signal-to-noise ratios and the BER for different
modulation schemes are deduced to provide useful insights into the impact of
system and channel parameters of the overall system performance. These accurate
expressions are general, since they correspond to generalized fading in the RF
link and account for pointing errors, atmospheric turbulence and different
modulation schemes in the FSO link. The links between derived results and
previous results are presented. Finally, numerical and Monte-Carlo simulation
results are provided to demonstrate the validity of the proposed unified
expressions.
