## 5 Results
### Performance Tests  
#### 5.1.1 iPerf Test  
For this test, an iPerf [28] test was run while the robot was developing a trajectory. iPerf is a network testing tool used to measure the bandwidth and performance of IP networks by generating TCP and UDP traffic between two hosts. When running iPerf, the network test has high priority over other data. This is important because it provides reliable, detailed statistics on network throughput and packet loss, making it useful for diagnosing network issues and optimizing performance.  
Configuration parameters of the VLC modem (LumaX) were selected to demonstrate the best performance in a water-tank environment with moderate lighting and a short distance of less than 12 m. These parameters are shown in Figure 5. The optical speed used for the four experiments was 6 MHz.  
The first experiment (Figure 6) was a straight-line trajectory. It can be observed that the values of bandwidth remain stable within a range of 4 to 5 MHz, independent of the distance from the VLC modem mounted on the robot and the fixed one. In this no-lost connection case, the modems were aligned (maximum deviation of 12 deg), and the maximum distance was 8 m.  
The second experiment (Figure 7) consists of three horizontal movements at different distances (2, 4, and 6 approx) with a minimum rotation of the robot. The objective of this experiment is to determine the field of view of the LumaX modems. According to the manufacturer, the field of view is a beam pattern of 120 degrees. The graphs show that, as in the first experiment, the bandwidth remains stable within a range of 4 to 5 MHz, except for a small period before the 100 th second, where the robot was outside of the field of view. Using the last measurement before the connection was lost (x = 1.21 m, y = 1.863 m, and z aligned), the Field of View (FoV) can be calculated using the Pythagoras theorem.  
\[FoV =2*\theta=\arctan\left(\frac{1.863\text{ m}}{1.21\text{ m}}\right) \tag{5}\] \[FoV \approx 2*\arctan(1.5397)\approx 115.12^{\circ} \tag{6}\]  
Figure 5: LumaX configuration parameters.  
In the third experiment (Figure 8), the robot navigated in a straight path, and at three different distances, it rotated to both limits where the connection was lost to test the field of view of the LumaX modem. The FoV of the first rotation was 148.031 degrees; in this case, the FoV was affected principally by the short distance and the reflections of the light. In the second rotation, the FoV was 109.12 degrees; this value is closer to the value reported by the manufacturer. In last rotation shows, the FoV was 75.25 degrees; here, the distance was around 7 m. This experiment implies that the longer the distance between the modems, the shorter the FoV.  
Lastly, experiment 4 (Figure 9) was performed verify the bandwidth. In experiment 4, the bandwidth did not change much with distance, as long as the distances were short (less than 12 m), with tank conditions and the modems are aligned.  
Table 5 shows the average intervals of the iPerf results for the four experiments. This table highlights that the metrics are generally consistent across experiments, except in cases where connection loss occurred, leading to a decrease in the average bits per second (bps). Additionally, the average Round-Trip Time (RTT) is approximately 42 ms, indicating that teleoperation of the robot using this channel is feasible.  
Figure 8: Experiment 3 –iPerf results after rotations at different distances using a 6 MHz optical speed.  
Figure 7: Experiment 2 –iPerf results after horizontal trajectories using a 6 MHz optical speed.