## 5 Experimental Results
### Experimental Procedure and Methods
#### 5.3.1 Indoor Testing Scenario and Results  
The indoor experimental evaluation followed the path described in Section 5.1 and illustrated in Figure 10. Table 7 resumes the experimental results for the indoor evaluation. As one can see, the experimental results show that the VLC prototype is able to sustain a communication range of up to 40 m (restricted due to the length of the laboratory) even in light dimming conditions. Therefore, the VLC receiver is able to maintain a BER of \(10^{-6}\) for distances between 1 and 40 m, while the duty cycle decreases from 40% to 1%. These results are extremely important, as they show that, in certain conditions, the VLC system is able to maintain high reliability while the distance is increasing and the duty cycle is decreasing to very low values.  
As the BER results were not affected in any way by the duty cycle decrease, an optical noise source (see parameters in Table 5) has been used to depreciate the VLC channel. Therefore, the 420 W incandescent light source has been orientated toward the VLC receiver as illustrated in Figure 12. In such circumstances, when the VLC receiver is close to its maximum communication range and the amount of incident parasitic light  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Pulse Width**} & \multirow{2}{*}{**Modulation**} & **Data Rate (kB/s)** & **VLC Distance (m)** & **BER** & **Conditions** \\ \hline
1–40\% & VPPM & 10 & 1–40 & \textless{}10\({}^{-6}\) & High SNR conditions: no artificial light sources and limited daylight \\ \hline
1–40\% & VPPM & 10 & 1–40 & \textless{}10\({}^{-6}\) & Low SNR conditions: the VLC receiver is directly exposed to an incandescent light source of 18,500 \(\upmu\)W/cm\({}^{2}\) \\ \hline
2–40\% & VPPM & 10 & 1–40 & \textless{}10\({}^{-6}\) & Low SNR conditions: the VLC receiver is directly exposed to an incandescent light source of 26,000 \(\upmu\)W/cm\({}^{2}\) \\ \hline
1\% & VPPM & 10 & 1–35 & \textless{}10\({}^{-6}\) & Low SNR conditions: the VLC receiver is directly exposed to an incandescent light source of 26,000 \(\upmu\)W/cm\({}^{2}\) \\ \hline
1\% & VPPM & 10 & 35–40 & \textless{}1942 \(\times\) 10\({}^{-4}\) & Low SNR conditions: 26,000 \(\upmu\)W/cm\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table}
Table 7: Summary of the experimental results for the indoor tests.  
Figure 11: The effect of the pulse-width variation at the receiver level: (**a**) The light dimming effect; (**b**) The “lights-off” zone.  
pushes the VLC receiver close to its saturation limit, the number of bit errors significantly increases. Thus, one can see that in such an extreme case, a 1% duty cycle decrease (i.e., from 2% to 1%) increases the number of errors by two orders of magnitude. In these conditions, the 10\({}^{-6}\) BER is maintained for a distance of up to 35 m, whereas after that, the BER has increased to around 10\({}^{-4}\). This indicates that light dimming has a slightly negative effect on the SNR, and in turn, on the overall VLC performances.  
Figure 13 presents the signal reconstruction process at the VLC receiver level and it illustrates the impact of light dimming for a 40-m communication range. One can see that even if the SNR level is affected by parasitic light and by the increased communication distance, the adequate signal processing blocks are able to properly restore the data signal. This is possible due to an appropriate filtering mechanism, which enhances the SNR, due to the adaptive amplification, which compensates the attenuation caused by the increased distance, and due to the software decision algorithm, which enables proper data decoding even if the pulse-width recognition is slightly affected by the low SNR. All these mechanisms enable adequate data extraction even in unfriendly conditions.  
Figure 12: Indoor experimental setup.  
Figure 13: _Cont._