### Experimental Results  
#### 4.2.1 Experimental Results for the Visible Light Communications Component Evaluation  
One of the purposes of the experimental evaluation of the VLC component was to confirm the capacity of the system to reliably transmit data from the LED-based luminaire VLC transmitter to the VLC receiver. Compared to the vehicular VLC channel, which is primarily in outdoor conditions [37; 38; 39; 40], the indoor one is definitely less challenging, as it involves only a few meters' communication range, less optical interferences, and a smaller degree of unpredictability, so good results would be expected. Another purpose of this experimental investigation is to determine the system's ability to maintain the connectivity when the user (i.e., the VLC receiver) is moving inside the VLC transmitter area. To be effective, such a system should be able to maintain the connectivity even within a wider area, and not only under the luminaire. More precisely, as the VLC receiver is upwards oriented, when it is moving away from the VLC transmitter, the incidence angle is increasing. Nevertheless, as the current generated by the photodiode has an incident angle cosine dependency, whereas the luminaire has a light direction oriented downwards, toward the workspace, one can see that the communication link can be affected. Therefore, these experiments are also useful in determining the system's communication coverage for a given BER limit. Thirdly, the purpose of these experiments is to confirm the VLC system's ability to provide simultaneous light dimming and data communication. As energy efficiency is becoming a major preoccupation for human society, the compatibility with light dimming or the system's ability to work in situations in which the user does not need the lighting function become very important. Figure 5 exemplifies an oscilloscope capture showing the signals received by the VLC receiver. It also displays the manner in which the incident light is gradually transformed into a ready to use digital signal. Additionally, this figure illustrates the VPPM light dimming mechanism with its working principles and a brief comparison with the classical Manchester coding. As one can see, VPPM enables a wide control over the _lights-on_ period, and therefore, a good control over the light intensity. Additionally, as the \(T_{ON}\) is similar for bit 1 and bit 0, no light flickering is introduced. The summary of the experimental results resuming the VLC component performance is provided in Table 2. As expected, the high SNR corroborated with an optimized VLC hardware design enabled the system to provide and maintain an extremely low BER. Thus, a BER lower than \(10^{-7}\) is achieved without any use of error correcting techniques. For comparison, previous experience has shown that with an adequate hardware design and with an optimized software data extraction algorithm, a low BER can be maintained as long as the SNR does not get below a 0-1 dB limit [38; 39; 40]. The very low BER is also the result of the integration of an automatic gain control circuit within the VLC receiver. The AGC is constantly adjusting the signal amplification, compensating the decrease in the incident power, while also preventing over-amplification that could lead to signal distortion and in turn, to bit errors. Furthermore, the results of the intensive experimental evaluation showed that the VLC receiver is able to maintain this low BER even in light-dimming conditions, as well as in the situation in which the VLC receiver is moving away from the VLC transmitter center coverage area. Thus, it has been demonstrated that the system can provide connectivity for a circular region that can have a 3 m radius. However, as in the experimental setup, the lighting fixtures are placed 1.5 m away from each other: this demonstrates that the proposed design is more than suitable to ensure the coverage of the entire area, and that it can definitely be replicated for other areas as well.