## 3 Adaptive Field-of-View Visible Light Communication: Concept and Prototype Development
### Experimental Results
#### 4.2.2 Experimental Results Showing the Benefits of the Adaptive FoV VLC Receiver  
The following experiments aimed to determine the benefits associated with the use of the adaptive FoV VLC receiver in terms of the BER and link operability. For improved clarity, a preliminary experimental set was made in order to better illustrate the effect of the adaptive FoV. Thus, during these tests, the VLC receiver was exposed to a sunlight irradiance of around 50,000 uW/cm\({}^{2}\), and at an FoV of \(\pm 22^{\circ}\), the communication was lost. The FoV was decreased to \(\pm 19^{\circ}\) in order to regain the communication, and the BER was calculated. The FoV was further decreased gradually to \(\pm 7^{\circ}\), while the BER was monitored. Figure 6 shows an example of the signals received by the VLC receiver, whereas Figure 7 presents the evolution of the BER with respect to the FoV. As one can see, the FoV  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Moment of the Day**} & **Sun Elevation Relative** & **Sun Angle Relative to the VLC Receiver** & **Sun Azimuth Relative** & **Sun Azimuth Relative** & **the VLC Receiver** \\  & **(Real Value)** & **(Estimated Value)** & **(Real Value)** & **(Estimated Value)** \\ \hline
8 a.m. \(\div\) 9 a.m. & 9.75\({}^{\circ}\)–19.68\({}^{\circ}\) & Diffuse light & \(-137.15^{\circ}\div-125.56^{\circ}\) & Diffuse light \\ \hline
9 a.m. \(\div\) 10 a.m. & 19.68\({}^{\circ}\)–29\({}^{\circ}\) & Diffuse light & \(-125.56^{\circ}\div-112.68^{\circ}\) & Diffuse light \\ \hline
10 a.m. \(\div\) 11 a.m. & 29\({}^{\circ}\)–37.1\({}^{\circ}\) & Diffuse light & \(-112.68^{\circ}\div-97.62^{\circ}\) & Diffuse light \\ \hline
11 a.m. \(\div\) 12 p.m. & 37.1\({}^{\circ}\)–43.16\({}^{\circ}\) & Diffuse light & \(-97.62^{\circ}\div-79.67^{\circ}\) & Diffuse light \\ \hline
12 p.m. \(\div\) 1 p.m. & 43.16\({}^{\circ}\)–46.2\({}^{\circ}\) & Diffuse light & \(-79.67^{\circ}\div-58.99^{\circ}\) & Diffuse light \\ \hline
1 p.m. \(\div\) 2 p.m. & 46.2\({}^{\circ}\)–45.55\({}^{\circ}\) & \(>\)30\({}^{\circ}\) & \(-58.99^{\circ}\div-37.45^{\circ}\) & \(\succ-30^{\circ}\) \\ \hline
2 p.m. \(\div\) 2:30 p.m. & 45.55\({}^{\circ}\)–43.45\({}^{\circ}\) & \(>\)30\({}^{\circ}\) & \(-37.45^{\circ}\div-27.6^{\circ}\) & \(\succ-30^{\circ}\) \\ \hline
2:30 p.m. \(\div\) 3 p.m. & 43.45\({}^{\circ}\)–41.36\({}^{\circ}\) & \(>\)30\({}^{\circ}\) & \(-27.6^{\circ}\div-17.6^adaptation significantly improved the reliability of the link and enhanced the BER. Thus, as the FoV was reduced from \(\pm 22^{\circ}\), the link was reestablished, and the BER continued to decrease from values of around \(10^{-4}\) to values lower than \(10^{-7}\). Consequently, these results reemphasize the significant effect that an adaptive FoV has on the VLC link performance. The final experimental results provided the system's performance for an entire day, from 8 a.m. to 8 p.m. For these experiments, the BER was monitored in real time during one sunny day, from sunrise to sunset, from 8 a.m. to 8 p.m. A summary of the experimental results is provided in Table 2. To better emphasize the benefits of the adaptive mechanism, the FoV is also provided for each time interval. Additionally, Table 2 presents the sun's irradiance, measured at the VLC receiver level with a high-precision irradiance meter (Delta Ohm 2302), as well as the sun's location with respect to the VLC receivers. As previously shown in the experiments summarized in Figure 7, the adaptive FoV of the VLC receiver 1 was able to maintain the active link while using varying FoVs, which, in turn, led to better  
Figure 6: Oscilloscope screen showing the signal received by the VLC receiver. Figure 7: Evolution of the BER with respect to the VLC receiver’s field of view for a 50 m link under exposure to intense indirect sunlight. or worse BER results. For example, under the same conditions, a BER ranging from \(10^{-7}\) and up to \(10^{-4}\) could be obtained.