## 4 Evaluation of the Logarithmic Transimpedance Circuit
### Experimental Evaluation in Long Range Outdoor Conditions
Concluding Remarks Regarding the Experimental Evaluation of the VLC Sensor Based on Logarithmic Transimpedance Circuit and on Its Compatibility to Vehicular Communications  
_Debate on the Proposed Vehicular VLC System Performances_  
The experimental results indicated that the system is able to support communication distances of 50 m while providing a BER as low as \(10^{-6}\). Furthermore, the experiments confirmed the advantages of VLC sensors based on logarithmic transimpedance circuits, showing that this approach enables the sensors to work in very strong background lighting conditions. Consequently, the performances of such systems are more than decent compared to the ones achieved by some of the best existing VLC systems. Experimental results also reconfirmed the important influence of the receiver FOV on the communication performances. Thus, when a wide FOV is selected, the amount of background light that is captured influences the SNR, and in turn, the BER performances. The most important contribution of this article is represented by the integration and evaluation of the logarithmic transimpedance circuit as an alternative to the linear transimpedance circuit in the automotive VLC sensors development. According to the results of the experimental investigations, the logarithmic transimpedance circuit provides the VLC sensor with improved performances in strong background light conditions as it prevents the saturation of the photosensitive element. Thus, VLC systems designed using this approach become more efficient in environments where the background light power varies significantly (i.e., automotive applications). As demonstrated in all simulations and experiments presented in Section 4, the logarithmic transimpedance circuit is able to prevent photodiode saturation. Nevertheless, as the intensity of the incident noise increases, the amplitude of the output data signal decreases. Consequently, in strong parasitic lighting conditions associated with low power data signals, the circuit provides a low SNR data signal. From this point on, the information decoding ability is given by the capacity of the signal processing plan to eliminate the noise and to reconstruct the data signal based on a low SNR signal. For comparison, a linear transimpedance circuit operating in similar conditions would have provided no information at all, as it would have been saturated. To further address this issue and to further improve the performances of such VLC sensors, new signal processing techniques are being investigated. Previous research has indicated that the performances of a VLC sensor can be significantly enhanced by means of digital signal processing [21]. Furthermore, the overall performances of a VLC system can be improved by developing hardware systems that are able to evaluate the environment conditions and the existing context, and which  
Figure 9: BER as a function of the SNR. adapt their behavior (i.e., hardware design, signal processing plan, communication parameters, etc.) in accordance with the existing conditions/environment/setup [22]. Based on these facts, our current work involves the usage of combined analog and digital signal processing techniques having adaptive features controlled by a data processing unit. Thus, we are optimistic concerning the usage of VLC technology in automotive applications, not only in short range communications, in indirect light exposure, or in perfect weather, but also in unfriendly conditions. Thus, this article represents a major step forward in this direction as it is experimentally confirms a VLC link in long range, direct sunlight conditions, and with a standard power VLC emitter. The proposed VLC system based on logarithmic transimpedance has been evaluated under variable scenarios and noise conditions in order to demonstrate the compatibility of VLC systems with vehicular communication applications. The experimental evaluation of the proposed approach confirms suitability of the design and the potential of VLC technology in automotive applications.