## 4 Experimental Setup  
The underwater robot used for this experiments is the Girona500 from IquaRobotics [22] (Parc Cientific i Tecnologic UdG, Edifici Giroempren. Pic de Peguera, 11, 17003 Girona (Girona), Spain). The dimensions of this robot are 1 m in height, 1 m in width, 1.5 m in length, and approximately 200 kg. This vehicle has 5 thrusters and is designed to provide passive stability in roll and pitch and to operate at a maximum depth of 500 m. The payload is equipped with a Reach Bravo 7 arm [23] for manipulation tasks. Navigation sensors are also available on the robot, including a Doppler Velocity Log (DVL), Attitude and Heading Reference System (AHRS), Global Positioning System (GPS), Ultra-Short Baseline (USBL), and pressure gauges, all of which are mixed in the Cola2 architecture [24] (Component-Oriented Layer-based Architecture for Autonomy). This ROS-based software architecture includes a full control stack, a localization module with a navigation filter, safety nodes, and all the drivers to communicate with the hardware.  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Mode/Parameter** & ** TBF** & **Scale** & **Quality** & **RGB or Grayscale** \\ \hline Manual & Open loop & Fixed & Fixed & Fixed \\ \hline Adaptive & Closed loop & Automatic & Automatic & Automatic (if operator permits) \\ \hline Scale Priority & Closed loop & Fixed & Automatic & Automatic (if operator permits) \\ \hline Quality Priority & Closed loop & Automatic & Fixed & Automatic (if operator permits) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Operation modes.  
In terms of communications, this robot can communicate through air using Wi-Fi and radio signals. Underwater communication can be achieved using 3 different channels: using a tether cable, an acoustic modem from Evologics [25], or a LumaX optical communications modem [26] added to the payload to increase the level of autonomy and overcome tether management problems. The left side of Figure 3 shows the underwater robot, and the right side shows the optical modem used for experiments.  
The experiments were conducted at the Research Centre for Robotics and Underwater Technologies (CIRTESU), Castellon de la Plana, Spain where there is a water tank with dimensions of 8 \(\times\) 12 \(\times\) 5 m and a control station next to it. From the control station, the tank is visible through the glass, allowing the light of the VLC modem to pass through and communicate with the one fixed on the underwater robot. Figure 4 shows a top-view diagram of the experimental setup in the CIRTESU tank.  
At the control station, an MSI GE 76 RAIDER (901 Canada Court, City of Industry, CA, USA) with Ubuntu 20.04 installed, an Intel i7 processor, 16 GB of RAM, an Nvidia Geforce RTX 3060, ROS Noetic, and Unity 2023.1 [27] serves as the ground controller. The VLC modems used in the experiment are the LumaX model from Hydromea [26] (Avenue de Longemalle 9, 1020 Renens, Switzerland). Finally, the PID parameters for the network congestion control algorithm used for the experiments are shown in Table 4.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline P (Proportional) & 10 \\ \hline I (Integral) & 1 \\ \hline D (Derivative) & 3 \\ \hline \hline \end{tabular}
\end{table}
Table 4: PID Controller Gains.  
Figure 4: Experimental setup at CIRTESU.  
Figure 3: Left: Girona500 AUV; LumaX modem used in the experiments.