## 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
Under such conditions, the system should consider a tradeoff between the importance of the BER and a wide FoV. In the following experiments, a low BER was considered to be a higher priority. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & \multicolumn{2}{c}{**Sun**} & & & \\ \multirow{2}{*}{**Hour of the Day**} & \multirow{2}{*}{**Sum**} & \multirow{2}{*}{**Sun**} & \multirow{2}{*}{**Irradiance**} & \multirow{2}{*}{**Adapted FoV**} & \multirow{2}{*}{**BER at VLC**} & \multirow{2}{*}{**BER at VLC**} \\  & & **Azimuth with** & & **Elevation with** & & **Measured at** & **for VLC** \\  & **Respect to VLC** & **Respect to VLC** & & **receiver 1** & & **receiver 1** \\  & **Receiver** & **Receiver** & & **[\(\mu\)W/cm\({}^{2}\)]** & & & \\ \hline
8 a.m. & \(-137.15^{\circ}\) & 9.75\({}^{\circ}\) & 2780 & \(\pm 22^{\circ}\) & \multirow{2}{*}{\(<\)\(10^{-7}\)} & \multirow{2}{*}{\(<\)\(10^{-7}\)} \\ \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & & \\
9 a.m. & \(-125.56^{\circ}\) & 19.68\({}^{\circ}\) & 4400 & \(\pm 19^{\circ}\) & & \\ \hline
9 a.m. & \(-125.56^{\circ}\) & 19.68\({}^{\circ}\) & 4400 & \(\pm 19^{\circ}\) & & \(10^{-6}\) \\ \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(<\)\(10^{-7}\) & \(-\) \\
10 a.m. & \(-112.68^{\circ}\) & 29\({}^{\circ}\) & 7090 & \(\pm 15^{\circ}\) & & \(10^{-5}\) \\ \hline
10 a.m. & \(-112.68^{\circ}\) & 29\({}^{\circ}\) & 7090 & & & \(10^{-5}\) \\ \(-\) & \(-\) & \(-\) & \(-\) & \(\pm 15^{\circ}\) & \(<\)\(10^{-7}\) & \(-\) \\
11 a.m.* & \(-97.62^{\circ}\) & 37.1\({}^{\circ}\) & 9700 & & & \(10^{-4}\) \\ \hline
11 a.m. & \(-97.62^{\circ}\) & 37.1\({}^{\circ}\) & 9700 & \(\pm 15^{\circ}\) & & \(10^{-4}\) \\ \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(<\)\(10^{-7}\) & \(-\) \\
12 p.m.* & \(-79.67^{\circ}\) & 43.16\({}^{\circ}\) & 3640 & \(\pm 22^{\circ}\) & & \(<\)\(10^{-6}\) \\ \hline
12 p.m. & \(-79.67^{\circ}\) & 43.16\({}^{\circ}\) & 3860 & \(\pm 22^{\circ}\) & & \(10^{-6}\) \\ \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(<\)\(10^{-7}\) & \(-\) \\
1 p.m.* & \(-58.99^{\circ}\) & 46.2\({}^{\circ}\) & 7100 & \(\pm 15^{\circ}\) & & \(10^{-5}\) \\ \hline
1 p.m. & \(-58.99^{\circ}\) & 46.2\({}^{\circ}\) & 41,700 & & & \\ \(-\) & \(-\) & \(-\) & \(-\) & \(\pm 7^{\circ}\) & \(<\)\(10^{-7}\) & link loss \\
2 p.m. & \(-37.45^{\circ}\) & 45.55\({}^{\circ}\) & 43,200 & & & \\ \(-\) & \(-\) & \(-\) & \(-\) & \(\pm 7^{\circ}\) & \(<\)\(10^{-7}\) & link loss \\
2:30 p.m. & \(-27.6^{\circ}\) & 43.45\({}^{\circ}\) & 47,400 & & & \\ \(-\) & \(-\) & \(-\) & \(-\) & \(\pm 7^{\circ}\) & \(<\)\(10^{-7}\) & link loss \\
3 p.m. & \(-17.6^{\circ}\) & 41.36\({}^{\circ}\) & 52,000 & & & \\ \(-\) & \(-\) & \(-\) & \(As one can see, in the morning between 8 a.m. and 11 a.m., when the sun was located to the left of the VLC receiver and outside the FoV, the adaptive mechanism of receiver 1 adjusted the FoV from \(\pm 22^{\circ}\) during the first hour in the morning to \(\pm 15^{\circ}\) when the irradiance reached values as high as 9700 \(\upmu\)W/cm\({}^{2}\). During this time, the two VLC receivers had a similar BER in the first hour, but the BER of receiver 2 increased rapidly towards \(10^{-4}\) from 9 a.m. to 11 a.m. Over the next two hours, from about 11 a.m. to 1 p.m., some clouds cast shadows over the area, so the irradiance went up and down to a minimum of around 3640 \(\upmu\)W/cm\({}^{2}\). As a result, receiver 2 maintained the link, but at a rather high BER with respect to the adaptive receiver. From 1 p.m., the clouds were gone and the sun intensity regained its power and started increasing to a maximum of 67,000 \(\upmu\)W/cm\({}^{2}\), so that adaptive VLC receiver 1 decreased its FoV to a minimum of \(\pm 7^{\circ}\), preventing the degradation of the SNR and maintaining the BER at values below \(10^{-7}\). For comparison, non-adaptive VLC receiver 2 could not be synchronized, resulting in a link loss. Starting at 3 p.m., the sun entered the FoV of both receivers.