## 5 Applications and Challenges of VLC in Underwater Systems  
### Applications of Underwater VLC  
VLC has recently been gaining popularity in the underwater environment since it offers high data rates and low latency and can be used both for illumination and communication. VLC is useful for underwater research due to its reliable data exchange among underwater sensors and AUVs, which is highly important in monitoring both underwater life and environmental parameters. The research [7] illustrates, for example, that VLC is able to provide real-time data collection and thus provides disturbance-free interaction of scientists with the ecosystem underwater in an interactive manner. Ref. [50] points out the advantage of VLC while transmitting data from sensors on temperature, salinity, and pressure by offering better ecological monitoring. The immediacy of the data can also enable underwater biologists to make observations about species behaviors, coral health, and ecosystem change, which is a very valuable tool for conservation and environmental research.  
VLC also plays an indispensable role in both underwater robotics and structure health monitoring, where the AUVs can employ high-speed short-range communications to send back above-water stations. The robots are enabled to construct, inspect, and structurally monitor certain subsea infrastructures, such as oil rigs, for safety and durability utilizing VLC in a variety of applications. Research such as [51] shows how VLC can support multiple devices together, allowing for seamless and continuous control from the ground station to the AUVs and sensor nodes across complex subsea environments. In addition, ref. [52] also supports VLC for secure and localized communications applications, especially in the protection of sensitive installations against intrusion or eavesdropping.  
VLC has been used for many applications, such as exploration and surveillance, whereby high-definition video transmission and large packets of data become important in the observation of real-time underwater habitats and the surveillance of sensitive areas.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Modulation Scheme** & **Data Rate** & **Distance** & **BER** & **Citation** \\ \hline OOK + Nonlinear Equalization & 100 Mbps & 100 m & \(10^{-5}\) & [28] \\ \hline QAM-OFDM & 4.92 Gbps & 1.5 m & \(10^{-6}\) & [32] \\ \hline PAM4 + Trellis Coding & 500 Mbps & 150 m & \(10^{-4}\) & [35] \\ \hline Diversity SiPM + DFE & 2 Gbps & 55 m & \(10^{-5}\) & [36] \\ \hline Hybrid QPSK-APSK & 3.18 Gbps & 56 m & \(10^{-4}\) & [44] \\ \hline Chaotic Encryption & 2.1 Gbps & 1.2 m & \(10^{-6}\) & [49] \\ \hline Adaptive QAM-OFDM + RIS & 5 Gbps & 100 m & \(10^{-6}\) & Proposed \\ \hline \hline \end{tabular}
\end{table}
Table 3: Performance comparison with recent state-of-the-art UVLC schemes.  
Ref. [53] provides evidence that the high data rate of VLC, achieved with spatial division and pairwise coding, supports applications like underwater video streaming and real-time surveillance in the conduct of underwater research and for defense purposes. Robustness against such combined disturbance of environmental or bubble turbulence will enhance the reliability of VLC in dynamic underwater conditions, which is a key element for missions demanding high-quality data transfer. Besides energy efficiency improvements, ref. [26] show that energy harvesting can be enabled by the VLC system, contributing toward sustainability regarding underwater sensor networks useful for IoUT applications in extending the mission within remote underwater regions.