## 8 Discussions on the Results, Contributions of this Work, and Perspectives  
One of the most important aspects that emerges based on the experimental results analysis is related to the opportunity of using the VLC technology in V2V applications. As the results show, BERs as low as \(10^{-7}\) can be achieved for relatively long distances, even without the use of forward error correcting protocols, whereas the use of such techniques  
Figure 12: Experimental BER results for the evaluation of the vehicle-to-vehicle VLC link in uncontrolled day conditions: (**a**) for a \(\pm 53^{\circ}\) reception angle; (**b**) for a \(\pm 20^{\circ}\) reception angle. can further improve these results. In terms of communication range, the experiments demonstrated a maximum communication distance of 75 m. As far as we know, this is the longest V2V VLC link established based on a set of commercial vehicle rear lights. Moreover, this communication distance could be further increased for the case of emergency brake applications as the irradiance distribution of vehicle brake lights is significantly higher than the one of the VLC emitter used for these tests. In comparison, the V2V VLC system evaluated in [36], provided a communication distance of less than 20 m, whereas the system from [44] can deliver ranges up to 45 m. It should be pointed out here that the current research focused on automotive VLC systems is mainly orientated toward traffic Infrastructure-to-Vehicle (I2V) connections, as the VLC emitters developed based on transportation infrastructure elements (i.e., traffic lights, street lighting systems) have a significantly higher optical power, enabling longer communication distances. Even so, there are only few works [30; 31] that report I2V-related VLC results with communication ranges above 75 m, whereas most of the existing systems provide communication distances of up to 50 m [21; 22; 23; 24; 26; 27; 28]. In this context, the 75 m communication range reported in this work provides important evidence that, step by step, the performances of automotive VLC systems are improving. Another very important aspect that results from the experimental tests is related to the fact that the VLC technology is able to provide V2V connectivity, even in vehicle misalignment conditions. Although the issues related to the effect of vehicle misalignment on V2V VLC performances have been theoretically analyzed in other works [49; 50; 57; 58], this is the first work that provides a consistent experimental evaluation of such a scenario, while providing a step by step comparison with the case when the vehicles are aligned. The authors of [44] provide a highly valuable experimental demonstration of a V2V VLC link in mobile conditions, and identify the distance and the incidence angle as the two main problems affecting the performances of such connections. Nevertheless, the authors of [44] do not provide a comprehensive analysis of the vehicle misalignment problem. In this context, this article shows that: (i) vehicle misalignment influences the performances of the V2V link in terms of minimum communication distances, which are determined by the VLC receiver's FOV; this leads to an initial zone where there is no connectivity, followed by a region where the BER is significantly higher compared to the case when the vehicles are aligned; (ii) optical lens, optical filters and adequate signal processing reduce the effect of vehicle misalignment for distances above the minimum distance, enabling the VLC system to provide BERs of the same order for both situations (i.e., vehicles on the same lane, or on adjacent lanes). To do so, the VLC receiver must be able to actively compensate the fact that the received optical power is decreasing, affecting in turn the SNR; (iii) as the longitudinal inter-vehicle distance is increasing, the incidence angle \(\alpha\) at the VLC receiver decreases and the effect of vehicle misalignment is mitigated. From this point, the performances of the V2V VLC link will predominantly be affected by the increasing distance.