## 3 Adaptive Field-of-View Visible Light Communication: Concept and Prototype Development
### Discussion on the Experimental Results, and Future Perspectives  
The experimental evaluation of the proposed adaptive FoV VLC receiver demonstrated the benefits and advantages of this concept. As has been shown, the proposed concept has the potential to significantly improve the resilience of VLC receivers to noise while maximizing the FoV, and in turn, the systems' mobility. Basically, establishing an optimal tradeoff between the resilience to optical noise and the compatibility with mobile conditions is an important challenge in the vehicular VLC domain [12; 44]. In this context, implementing and experimentally testing such a concept represents an important step toward the deployment of this technology. It should be reemphasized that the testing setup was envisioned to take the communication link to its limits in order to better emphasize the effect of the optical interference. From this perspective, the experimental results showed that, although the non-adaptive VLC receiver was able to support a 50 m communication range, the reliability of the link was strongly affected by optical noise. Thus, as the irradiance of the optical noise increased, the BER decreased and the link was eventually lost. On \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \begin{tabular}{c} **Sun** \\ **Azimuth with** \\ **Despect to VLC** \\ **Receiver** \\ \end{tabular} & \begin{tabular}{c} **Sun** \\ **Elevation with** \\ **Respect to VLC** \\ **Receiver** \\ **Reciver** \\ **[\(\upmu\)W/cm\({}^{2}\)]** \\ \end{tabular} & \begin{tabular}{c} **Sun** \\ **Iradiance** \\ **Measured at** \\ **the VLC** \\ **Receiver 1** \\ **[\(\upmu\)W/cm\({}^{2}\)]** \\ \end{tabular} & \
\begin{tabular}{c} **Adapted FoV** \\ **for VLC** \\ **Receiver 1** \\ **(with Adapted** \\ **FoV)** \\ \end{tabular} &
\begin{tabular}{c} **BER at VLC** \\ **Receiver 2** \\ **(with Fixed** \\ **FoV)** \\ \end{tabular} \\ \hline
5:30 p.m. & 21.19\({}^{\circ}\) & 21.1\({}^{\circ}\) & 8100 & \(\pm 15^{\circ}\) & \(10^{-5}\) \\ – & – & – & – & – & \(<\)\(10^{-7}\) & – \\
6 p.m. & 25.87\({}^{\circ}\) & 16.32\({}^{\circ}\) & 4300 & \(\pm 22^{\circ}\) & \(10^{-6}\) \\ \hline
6 p.m. & 25.87 & 16.32\({}^{\circ}\) & 4300 & & \(10^{-6}\) \\ – & – & – & – & \(\pm 22^{\circ}\) & \(<\)\(10^{-7}\) & – \\
7 p.m. & 37.23\({}^{\circ}\) & 6.31\({}^{\circ}\) & 2100 & & & \(<\)\(10^{-7}\) \\ \hline
7 p.m. & 37.23\({}^{\circ}\) & 6.31\({}^{\circ}\) & 2100 & & & \\ – & – & – & – & \(\pm 22^{\circ}\) & \(<\)\(10^{-7}\) & \(<\)\(10^{-7}\) \\
7:45 p.m. & 45.08\({}^{\circ}\) & 0.83\({}^{\circ}\) & 980 & & \\ \hline \hline \end{tabular}  
* Between 10:50 a.m. and 12:45 p.m., the sky was cloudy; ** between 5 p.m. and 5:30 p.m., the sun irradiance suddenly dropped due to a tree that blocked the line of sight between the sun and the VLC receiver.  
\end{table} 
Table 2: _Cont._the other hand, the adaptive FoV VLC receiver was able to constantly compensate for the effects of the optical noise and maintain the BER at values lower than \(10^{-7}\). Consequently, it is obvious that the adaptive FoV architecture had a positive effect on the communication performance in terms of the BER and stability, while ensuring a decent FoV. Additionally, this architecture enabled the VLC receiver to regain its FoV once the effect of the optical noise was reduced. Therefore, enabling a VLC receiver to adapt to the environmental conditions significantly improves its performance. On the other hand, as this is still a work in progress, we can say that the FoV adaptation algorithm is still perfectible, and from this point of view, excessive FoV narrowing has been experienced. Although correlating the FoV with the noise intensity proved to be an adequate option, additional aspects should be considered. During these tests, it was observed that sometimes the multi-angle sensor was given ambiguous values at two or three adjacent photodiodes, so the position of the sun was not determined with great accuracy.