## 7 Experimental Results
### The Experimental Evaluation of the Effect of Vehicle Misalignment and of Inter-Vehicle Distance  
Once the validation of the VLC emitter confirmed that its irradiation pattern is within the specifications of the existing standards, the next step is to provide an empirical evaluation of the VLC receiver's ability to reconstruct the data signal and most importantly, to evaluate the effects of vehicle misalignment on the received signal. Therefore, Figure 10 illustrates the signal processing at the VLC receiver level, marking the most important signal reconstruction steps. In order to clearly illustrate the effect of the variable distance and of the vehicle misalignment on the received data signal, these oscilloscope print screens show the measurements taken in night conditions with a limited effect from the outdoor fluorescent lighting system, while using a wide FOV. Thus, Figure 10 focuses on the effect of vehicle misalignment and of the increasing inter-vehicle distance. As one can see, at a short distance (i.e., 4 m in this case), the effect of vehicle misalignment is very stringent, as the amplitude of the front-end stage (i.e., channel 1 signal) is about 20 times lower compared to the case when the vehicles are on the same lane (Figure 10a,b). Although these experiments have been performed in night conditions, the SNR level is low, but the VLC receiver is able to properly reconstruct the data signal. Nevertheless, existing experience indicates that in daytime conditions, the corroboration of vehicle misalignment and of parasitic sunlight could have a highly disruptive effect on the SNR level and in turn, on the overall communication parameters. Going further, as the inter-vehicle distance increases, the incidence angle \(\alpha\) at the VLC receiver decreases and the influence of vehicle misalignment is less pronounced. Thus, at 10 m, the amplitudes of the signals differ by about six times (see Figure 10c,d, channel 1), whereas at 35 m, the two signals have approximately the same amplitude (see Figure 10e,f, channel 1). Figure 9: VLC emitter prototype irradiance distribution. Figure 10: Oscilloscope print screens showing the signal reconstruction process at the level of the different blocks of the VLC receiver: Channel 1 (orange) shows the output of the optical receiver for a 40 dB gain; Channel 2 (cyan) shows the output of the band-pass filter; Channel 3 (purple) shows the output of the amplification block; Channel 4 (green) shows the reconstructed signal which will be used in the data decoding process: (**a**) vehicles on the same lane with 4 m inter-vehicle distance; (**b**) vehicles on adjacent lanes with 4 m inter-vehicle longitudinal distance (close to the minimum communication distance); (**c**) vehicles on the same lane at 10 m distance; (**d**) vehicles on adjacent lanes at 10 m inter-vehicle longitudinal distance; (**e**) vehicles on the same lane at 35 m; and (**f**) vehicles on adjacent lanes at 35 m inter-vehicle longitudinal distance. One can see that as the distance increases, the misalignment effect becomes less stringent. The results of the experimental investigation of the V2V VLC system for the two lane scenario are summarized in Figures 11 and 12. Thus, Figure 11 illustrates the BER results for the experiments performed in night conditions under the influence of the fluorescent lights for wide and for narrow FOV, whereas Figure 12 presents the results of the tests in the same conditions, but during the day time. The experimental BER results clearly show the manner in which the vehicle misalignment influences the performances of V2V VLC links in terms of coverage, minimum reception distance, BER, and communication range. As expected, the effect of vehicle misalignment is stronger at short inter-vehicle longitudinal distances.