# Laser-Based Mobile Visible Light Communication System
## 3 Results and Discussion
Interestingly, data deviation occurred in both stationary and mobile contexts, with comparable frequencies. As shown in Figure 7b, whether in stationary and mobile conditions, the majority of the BER data points clustered around 5.0 \(\times\) 10\({}^{-4}\). However, there were a few points that appeared at values exceeding 1.0 \(\times\) 10\({}^{-3}\). We tend to believe that this was brought about by having environmental perturbations and judgment error rather than the movement of the receiving end. Consequently, we excluded these environmental factors and focused on the boxed portion of data for further observation. As illustrated in Figure 7d,e, an increase in distance introduced instability to the system, gradually widening the BER distribution range. Moreover, the impact of the mobile receiver on the system performance became more pronounced, with the BER distribution under mobile VLC conditions being noticeably more dispersed. At three meters in stationary conditions, the BER fluctuated within a range from approximately 2.0 \(\times\) 10\({}^{-4}\) to 6.0 \(\times\) 10\({}^{-4}\), while in mobile conditions, this extended to a range from 1.5 \(\times\) 10\({}^{-4}\) to 7.0 \(\times\) 10\({}^{-4}\). At this point, the moving receiver had already exerted a certain influence on the system's performance, resulting in a less stable distribution of the BER. At four meters, the distinction between stationary and mobile systems became more pronounced. In stationary conditions, the distribution of the BER was relatively concentrated, ranging from around 5.0 \(\times\) 10\({}^{-4}\) to 1.5 \(\times\) 10\({}^{-3}\). However, in mobile conditions, the BER was more dispersed, with distributions ranging from 5.0 \(\times\) 10\({}^{-4}\) to 3.5 \(\times\) 10\({}^{-3}\). To observe this more clearly, the experiment calculated the standard deviation of the BER from 1 m to 4 m for both stationary and mobile VLC, as shown in Figure 7f. At a distance of 1 m, the significant variation in the BER across different stationary positions resulted in a larger standard deviation for the stationary BER at this distance, exceeding that of the mobile condition. At distances of 2 m, 3 m, and 4 m, the standard deviation for mobile conditions consistently surpassed the level in stationary conditions. Furthermore, as the distance increased, both the stationary and dynamic standard deviations gradually rose, with the disparity between them continuously expanding. Lastly, we further assessed the impact of the receiver's moving speed on the system performance. Under varying distances from 1 m to 4 m, the system's BER at different speeds (excluding environmental factors) is depicted in Figure 8. 1 S/r represents that the rotor completes one round per second, resulting in the mobile platform moving 162 mm. Our selected range for rotation speed ranged from 0.1 S/r to 3.0 S/r, with a corresponding speed of 0.48 m/s at 3.0 S/r. We opted to test at a speed of 0.48 m/s, taking into account the typical pace of movement for individuals within indoor settings. By simulating this common speed, we aimed to evaluate the performance and feasibility of our system under conditions reflective of everyday movement within indoor spaces. We tested about 40 sets of data at 1 m, 30 sets at 2 m, and 20 sets at 3 m and 4 m at each speed. The number of tests remained consistent across different velocities at the same distance. Then, we sorted the data obtained from the experiment from small to large to facilitate our subsequent drawing. Figure 7: (**a**–**c**) distribution of stationary and mobile VLC BER at 2 m, 3 m, and 4 m. (**d**,**e**) partial enlargement of the boxes in (**b**,**c**) at 3 m and 4 m. (**f**) Comparison of standard deviation of BER between stationary and mobile VLC. After sorting, we used different colors to represent the relative size of the data. The blue part represents the smaller part of the BER, and the red part represents the larger part of the BER. Each small color block in the picture are the data obtained from one test.