## 4 Experimental Results
### Experimental Results of the Proposed Vehicular VLC System Under Various Scenarios  
To validate the adaptive beam alignment system in the proposed vehicular VLC system, we conducted an additional empirical experiment. In this experiment, the system's performance was analyzed through a comparison of two cases: (i) with the adaptive beam alignment system activated and (ii) without adaptive beam alignment. The measurements were carried out while varying the misalignment angle between the transmitter and receiver of consecutive vehicles. As shown in Figure 11, the system incorporating the adaptive beam alignment maintained a stable SINR across the considered range of misalignment angles. In contrast, the system without adaptive alignment exhibited a significant degradation in  
Figure 10: Comparison of acceleration and target speed data among the leading, middle, and trailing vehicles, when encountering stationary leading vehicle in scenario 2.  
SINR as the misalignment angle increased. These findings demonstrate the critical role of the adaptive beam alignment system in preserving communication robustness, particularly under the non-ideal alignment conditions commonly encountered in real driving scenarios.  
In addition, Figure 12 shows the SINR performances of the proposed system under two conditions--with and without tunnel lighting--while varying the misalignment angle between the transmitter and receiver of consecutive vehicles. Since tunnel lighting typically uses white LED light, we replicated this condition in our experiment by using a comparable white LED light source to simulate realistic tunnel lighting interference. In Figure 12, it is identified that when the transmitter and receiver are well-aligned (i.e., misalignment angle = 0\({}^{\circ}\)), the presence of tunnel lights causes a slight reduction in SINR, but the overall performance remains robust. However, as the misalignment angle increases, the impact of tunnel lighting becomes more pronounced, leading to a larger degradation in the SINR. This indicates that tunnel lighting can act as a significant source of external interference, particularly when the optical beams are not perfectly aligned. These findings highlight the critical importance of the adaptive beam alignment system integrated into our design, which helps maintain a strong SINR even in the presence of ambient tunnel lighting. Furthermore, the results confirm that external lighting conditions must be carefully considered when designing and deploying VLC-based vehicular communication systems in real-world environments.  
Furthermore, we also conducted an empirical experiment to evaluate the feasibility of using a commercial LED tail-light as a transmitter in our VLC system. The results of this experiment are presented in Figure 13, which shows the SINR (in dB) and signal and noise power levels (in dBm) at varying distances between the transmitter and receiver. As expected, the SNR decreases as the distance increases, but the trend and absolute values confirm the feasibility of using vehicular LED tail-lights as VLC transmitters when supported by a suitable optical receiver design.  
Figure 11: Performances of the proposed vehicular VLC system with and without the adaptive beam alignment mechanisms.