## 4 Experimental Evaluation of the VLC System and Experimental Results
### Experimental Setup No. 4--Long Communication Distance in Outdoor Snowfall Conditions  
After presenting the experimental results in variable indoor conditions, the next step is to provide the experimental validation in outdoor surroundings. The logarithmic transimpedance circuit is able to significantly reduce the possibility of saturation, while expanding the sensor's dynamic range (i.e., the system is able to work in a wide range of background lighting), as shown in [31]. Thus, as verified in [31], the logarithmic transimpedance circuit enables the VLC receiver to provide a \(10^{-6}\)-\(10^{-3}\) BER at 50 m, in sunny day conditions (i.e., sunlight irradiance up to 67000 \(\upmu\)W/cm\({}^{2}\)). In addition to strong sunlight, snowfall represents the most important perturbing source for outdoor VLC, as demonstrated in [40]. Snowfall can reduce the communication range by up to 60-80%, according to [40]. Consequently, the following test is evaluating the proposed VLC system performances in snowfall conditions for a 50 m communication range. In addition to distance and snowfall, the VLC channel is also affected by heavy blizzard episodes. The summary of the weather conditions during the experimental evaluation is available in Table 5, whereas a configuration of the VLC system during these tests is presented in Table 6.  
Figure 8 shows the experimental setup, whereas Table 7 shows the summary of experimental results. These results showed that snowfall has the potential to increase the number of bit errors by 100 times, whereas the number of bit errors can increase by up to 10,000 times when the snowfall is also associated to heavy gust. Thus, the experimental evaluation has confirmed the simulations from [40], demonstrating the highly disruptive effect of snowfall and blizzard. Figure 9 shows the real-time evolution of the BER for three data rates while using OOK modulation and Manchester coding. This figure shows the manner in which the BER evolves and how it is influenced by the intensity of the snowfall or of the wind gusts. \begin{table}
\begin{tabular}{c c} \hline \hline
**VLC System Feature** & **Configuration** \\ \hline Modulation & OOK \\ Coding & Manchester \\ Data rates & 11 kb/s; 24 kb/s; 50 kb/s \\ VLC distance & 50 m \\ VLC receiver FOV & \(\pm 15^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of the VLC system configuration during the outdoor tests in snowfall conditions. \begin{table}
\begin{tabular}{c c} \hline \hline
**Conditions** & **BER** \\ \hline Low parasitic lighting & \textless{}10^{-6} * \\ Snowfall conditions & \(4\times 10^{-5}\) \\ Snowfall and heavy gust conditions & Up to \(10^{-3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Summary of the experimental results in snowfall conditions. \begin{table}
\begin{tabular}{c c} \hline \hline
**Weather Parameter** & **Numeric Value Range** \\ \hline Temperature [\({}^{\circ}\)C] & \textless{}0.5—2.3 \\ Relative humidity [\%] & 94–96 \\ Snowfall amount [cm] & 1.5 \\ Shortwave radiation [W/m\({}^{2}\)] & 45–76 \\ Wind speed [km/h] & 60–63 \\ Wind gust [km/h] & 58–64 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of the weather conditions during the outdoor tests. One can also see from Figure 9 that, in this case, the experimental results show that the BER is decreasing as the data rate is increasing. Nevertheless, these results are influenced by the snowfall and the wind gust intensities, as the experiments have been made in uncontrolled snowing conditions. Figure 8: Experimental evaluation of the proposed vehicular VLC system in outdoor snowfall conditions for a 50 m VLC traffic light emitter to VLC receiver communication distance. In this setup, the VLC channel is perturbed by snowfall and heavy blizzard episodes. Figure 9: Real-time evolution of the BER results in snowfall and wind gust conditions. The peeks in the BER representation are generated by variations of snowfall intensity and by wind gusts.