# Laser-Based Mobile Visible Light Communication System
## 3 Results and Discussion
According to Figure 8, when transmitting data at 500 Mbps over distances of 1 m, the distribution of bit error rates for speeds ranging from 0.1 S/r to 3 S/r was concentrated between 5.7 \(\times\) 10\({}^{-5}\) and 2.88 \(\times\) 10\({}^{-4}\). At a 2 m distance, the distribution was concentrated between 1.0 \(\times\) 10\({}^{-4}\) and 3.46 \(\times\) 10\({}^{-4}\), while at a 3 m distance, it ranged from 1.58 \(\times\) 10\({}^{-4}\) to 5.76 \(\times\) 10\({}^{-4}\). For the 4 m distance, the distribution was concentrated between 3.8 \(\times\) 10\({}^{-4}\) and 3.54 \(\times\) 10\({}^{-3}\). While there was some overlap between these data points, their lower and upper bounds consistently exhibited a well-defined monotonic trend with distance. Specifically, as the distance increased, the error rate also tended to increase. The overlap might have been caused by the SiPM utilized as a detector in the experiment, which was highly sensitive. Even minor disturbances in the channel can lead to variations in the detection results. As evident from the static and dynamic BER distributions in Figure 7, the BER fluctuated within a certain range, even during stationary conditions. Therefore, it was inevitable that there would be fluctuations in the BER during the movement of the receiver on the track. Rather than comparing one single BER, we focused on the overall trend in the distribution range. For the 1 m and 2 m cases, as shown in Figure 8a,b, the BER across different speeds did not display a clear change, suggesting that the system's performance remained highly stable, even in the face of rapid movement. However, upon extending the transmission distance to 3 m in Figure 8c, it became apparent that, at lower speeds, the blue segment was longer and the red segment was shorter. At higher speeds, the length of the blue segment decreased while the red segment lengthened, indicating that the instability introduced by rapid movement resulted in an increase in the BER. This pattern in Figure 8d became even more evident at a transmission distance of 4 m. At speeds below 1.0 S/r, almost all bit error rates fell within the blue range. As the speed increased, the upper limit of the BER gradually rose, and by 3.0 S/r, nearly half of the BERs were in the red range, demonstrating  
Figure 8: (**a–d**) BER of the mobile VLC system for different receiver moving speeds at 1 m, 2 m, 3 m, and 4 m.  
significant variability in the system performance. However, it is noteworthy that the BER remained below \(3.8\times 10^{-3}\) throughout, indicating an effective transmitting system. We averaged the BERs measured at a certain distance for various speeds and plotted them in Figure 9. It is evident that, at a fixed distance, the BER increased gradually with the increase in speed, particularly noticeable at distances of 3 m and 4 m. On the other hand, when maintaining consistent speed parameters, as the distance between the transmitter and the receiver became larger, the BER also showed a trend of becoming larger. Overall, as the distance and speed increased gradually, the experimentally measured BER also increased accordingly. Conversely, when the distance was short and the speed was low, the BER tended to be at its lowest. This observed trend aligns well with common knowledge.