## 4 Experimental Evaluation of the VLC System and Experimental Results
### Experimental Setup No. 2--Medium Communication Distance in Low SNR Conditions  
The purpose of the following experimental setup is to investigate the influence of parasitic noise sources on the communication's performances. Another important aim for these tests was to confirm the benefits that are associated with the use of a logarithmic transimpedance circuit instead of the classical approach. For this setup, the emitter-receiver distance is maintained at 18 m, while a perturbing high power LED has been placed 17 cm from the receiver. The VLC sensor receives an additional direct optical noise of 190 \(\mu\)W/cm\({}^{2}\) due to the perturbing LED. Even though the noise source is directly facing the VLC receiver, whereas the received signal power is significantly lower, the VLC receiver is still able to extract the data. Figure 5 demonstrates the signal reconstruction process within the main stages of the VLC receiver. It illustrates the output of the logarithmic transimpedance circuit, the output of the first pre-amplification block, the output of the filters, and the reconstructed data signal. This figure also shows the sensor's response to the noise power increase (Figure 5b,c). One can see that, as the level of the received perturbing light is increasing, the logarithmic transimpedance circuit is counteracting this effect by automatically adjusting its response. Thus, the photoelectron saturation is prevented. The logarithmic transimpedance circuit response to mitigate the noise effect also leads to a decrease in the data signal amplitude. Nevertheless, the proper response of the AGC circuit compensates the above mentioned issue, whereas the reconstruction of the data signal is not affected. Table 3 presents the summary of these experiments. The experimental results showed that, even when a moderate noise source is perturbing the VLC receiver, it is still able to maintain the BER lower than \(10^{-6}\).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Modulation** & **Coding** & **Data Rate (kb/s)** & **VLC Distance (m)** & **BER*** \\ \hline DSSS & SIK & 3 & 18 & \textless{}10^{-6}\) \\ OOK & Manchester & 11 & 18 & \textless{}10^{-6}\) \\ OOK & Miller & 11 & 18 & \textless{}10^{-6}\) \\ OOK & Manchester & 24 & 18 & \textless{}10^{-6}\) \\ OOK & Manchester & 24 & 18 & \textless{}10^{-6}\) \\ OOK & Miller & 24 & 18 & \textless{}10^{-6}\) \\ OOK & Manchester & 50 & 18 & \textless{}10^{-6}\) \\ OOK & Miller & 50 & 18 & \textless{}10^{-6}\) \\ \hline \hline \end{tabular}  
* The BER \(<10^{-6}\) has been achieved based on a minimum 10 data sets, each test of one-million bits.  
\end{table}
Table 2: Summary of the experimental results for setup NO. 1.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Modulation** & **Coding** & **Data Rate (kb/s)** & **VLC Distance (m)** & **BER** \\ \hline DSSS & SIK & 3 & 18 & \textless{}10^{-6}\) \\ OOK & Manchester & 11 & 18 & \textless{}10^{-6}\) \\ OOK & Miller & 11 & 18 & \textless{}10^{-6}\) \\ OOK & Manchester & 24 & 18 & \textless{}10^{-6}\) \\ OOK & Miller & 24 & 18 & \textless{}10^{-6}\) \\ OOK & Manchester & 50 & 18 & \textless{}10^{-6}\) \\ OOK & Miller & 50 & 18 & \textless{}10^{-6}\) \\ \hline \hline \end{tabular}  
* The BER \(<10^{-6}\) has been achieved based on a minimum 10 data sets, each test of one-million bits.  
\end{table}
Table 3: Summary of the experimental results for setup NO. 2.