Aqua-Sense: Relay-Based Underwater Optical Wireless Communication for IoUT Monitoring

Underwater wireless optical communication (UWOC) performance is negatively impacted by challenges such as water turbulence, restricted range, and misalignment. These challenges can impact the feasibility of large-scale deployment. In comparison to conventional acoustic and radio frequency (RF) communication, UWOC can play a pivotal role in connecting various Internet of Underwater Things (IoUT) devices. This research presents the design and evaluation of "aqua-sense," a relay-based UWOC system aimed at enhancing communication link performance and expanding the reception area of the optical receiver. To harness diversity gain, the optical relay incorporates combining techniques such as Equal Gain Combining (EGC), Majority Logic Combining (MLC), and Selection Combining (SC) to enhance its performance. Additionally, the optical relay, referred to as the "opto-relay," is empowered by a channel-aware algorithm to further improve communication link performance. In moderately turbid water conditions with a turbidity level of 25 NTU, the aqua-sense system achieved a packet success rate of 68% at a communication link distance of up to 7.5 meters, transmitting at a rate of 0.2 Mbps. Additionally, the sensor node, "opto-sense," achieved a consistent transmission rate of 0.5 Mbps in clear water with a turbidity of 0.01 NTU. These results remained stable even when moderate water waves with a displacement rate of 5 liters/min and air bubbles with an airflow rate of 5 liters/min were present within a 2-meter communication link range.