## 6 Outdoor Testing Procedure  
The experimental evaluation of the VLC systems began with the examination of the VLC emitter prototype light radiation pattern. This investigation aimed to establish the similarity between the light radiation pattern of the VLC emitter and the one of commercial vehicles. Additionally, this examination should determine that the proposed VLC prototype is in accordance with existing standards imposed to vehicle lighting systems [66]. The light distribution measurement procedure is similar to the one followed for the determination described in Section 4, whereas the results are presented in Section 7.2. The second part of the experimental investigation is focused on determining the V2V VLC link performances and the effect of vehicle misalignment on the performances of such VLC applications. To this purpose, this article considers a two-lane scenario where the VLC emitter can be on the same lane or on the adjacent lane with respect to the VLC receiver. Based on this fact, the communication parameters could be influenced in terms of minimum communication distance, BER, and communication range. Therefore, in order to have an adequate assessment concerning the manner in which vehicle misalignment influences these parameters and to move forward from laboratory prototypes to vehicle embedded systems, extensive experimental investigation is required. The projected testing scenario is illustrated in Figure 1.  
Similar to the real case scenario, the dynamic situations imposed by the vehicle mobility do not guarantee that the vehicles (i.e., the VLC emitter and the VLC receiver) are in alignment with respect to each other. In order to determine the effect of vehicle misalignment, the V2V system was tested in outdoor conditions, on a two lane road, within \begin{table}
\begin{tabular}{c c c} \hline \hline
**VLC Receiver Stage** & **Parameter** & **Feature/Values** \\ \hline \multirow{4}{*}{Front-end} & VLC receiver FOV & \(\pm\)53\({}^{\circ}\) respectively \(\pm\)20\({}^{\circ}\) \\ \cline{2-3}  & VLC optical receiver & PDA100A optical detector with \\  & VLC receiver optical filter & \multicolumn{2}{c}{adjustable gain} \\ \cline{2-3}  & VLC receiver optical filter & \multicolumn{2}{c}{645 \(\pm\) 40 nm} \\  & center wavelength & \multicolumn{2}{c}{} \\ \hline \multirow{4}{*}{Signal conditioning} & Amplification & Up to 5000 gain, with automatic \\  & & gain control \\ \cline{2-3}  & & - & 1 kHz high-pass 2 nd order \\  & & Bessel filter \\  & Signal filtering & - & adjustable 4 th order Bessel \\  & & low-pass cut-off frequency filter \\  & & (200 kHz for these tests) \\ \cline{2-3}  & Square signal reconstruction & \multicolumn{2}{c}{Based on Schmitt trigger circuit} \\ \hline \multirow{4}{*}{Data processing} & Hardware & Microcontroller board based on an \\  & & ARM Cortex M4 180 MHz processor \\ \cline{2-3}  & Data processing & \multicolumn{2}{c}{Based on rising and falling edge} \\  & & identification and pulse \\  & & width measurement \\ \cline{2-3}  & & Real-time data extraction for data \\  & & modulated using DSSS and OOK \\  & & modulation, SIK, Manchester and \\  & & Miller coding, with data rates \\  & & between 3–200 kb/s \\ \cline{2-3}  & Monitored parameters & \multicolumn{2}{c}{Real-time BER computing without \\  & & forward error correcting codes} \\ \hline Other VLC receiver & \multicolumn{2}{c}{Height of the optical detector} & 74 cm \\ parameters & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of the VLC receiver parameters. the parking lot of the Stefan cel Mare University of Suceava. For this purpose, the VLC emitter (Tx vehicle in Figure 1) was placed on the second lane, whereas the VLC receiver (Rx vehicle in Figure 1) was alternatively placed on the first and on the second lane. The measurement procedure was begun from a one meter V2V longitudinal distance.