  In this work, we design and analyse a Slotted ALOHA (SA) solution for Optical
Wireless Communication (OWC)-based Internet of Underwater Things (IoUT). In the
proposed system, user devices exchange data with an access point (AP) which
exploits the capture effect. The space spanned by the IoUT nodes is
three-dimensional, i.e., users are located in half-sphere centered at the AP
placed at the bottom of a floating object at the water surface level. The
analytical expressions for the system throughput and reliability expressed in
terms of the outage probability are derived. Based on the simulated
signal-to-noise-and-interference-ratio statistics and derived analytical
expressions, we present numerical results that investigate the trade-off
between the system performance and the IoUT system parameters, such as the
number of users, activation probability and type of water medium. The presented
conclusions provide valuable insights into the design of an SA-based solution
for IoUT communications.
