  Multihop relaying is a potential technique to mitigate channel impairments in
optical wireless communications (OWC). In this paper, multiple fixed-gain
amplify-and-forward (AF) relays are employed to enhance the OWC performance
under the combined effect of atmospheric turbulence, pointing errors, and fog.
We consider a long-range OWC link by modeling the atmospheric turbulence by the
Fisher-Snedecor ${\cal{F}}$ distribution, pointing errors by the generalized
non-zero boresight model, and random path loss due to fog. We also consider a
short-range OWC system by ignoring the impact of atmospheric turbulence. We
derive novel upper bounds on the probability density function (PDF) and
cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio
(SNR) for both short and long-range multihop OWC systems by developing exact
statistical results for a single-hop OWC system under the combined effect of
${\cal{F}}$-turbulence channels, non-zero boresight pointing errors, and
fog-induced fading. Based on these expressions, we present analytical
expressions of outage probability (OP) and average bit-error-rate (ABER)
performance for the considered OWC systems involving single-variate Fox's H and
Meijer's G functions. Moreover, asymptotic expressions of the outage
probability in high SNR region are developed using simpler Gamma functions to
provide insights on the effect of channel and system parameters. The derived
analytical expressions are validated through Monte-Carlo simulations, and the
scaling of the OWC performance with the number of relay nodes is demonstrated
with a comparison to the single-hop transmission.
