## 8 Discussions on the Results, Contributions of this Work, and Perspectives
The experimental results also reconfirmed the importance of an adequate optical collecting front-end component showing the benefits of optical lens and of optical filters. The optical lenses increase the light-collecting region, whereas the optical filters only allow the passage of the wavelengths of interest. Therefore, both solutions contribute to an important SNR enhancement. Moreover, the usage of a narrow FOV further improves the SNR, as it eliminates part of the light coming from the sides but at the expense of an increased initial no-connection zone. Based on these techniques, one can see that the BER performances have been improved by up to four orders of magnitude, as it can be seen in Figure 12a,b for distances over 25 m. Moreover, the optical lens and the narrower FOV have increased the communication distance from 35 m to 75 m. On the down side, the narrow FOV makes it difficult for the VLC receiver to establish the LoS with the VLC emitter, affecting, in turn, the mobility. However, several solutions to this problem emerge. Cooperative and relay-assisted protocols are an example of such solutions where a VLC receiver that is not within the LoS with the VLC emitter receives the information with the help of an intermediate node. The efficacy of this method has been intensively investigated in indoor VLC applications [18; 19]. This solution has also been found to be suitable in inter-vehicle applications and the results showed that the connectivity on curved roads can be improved with the help of a relay vehicle [58]. Experimental demonstrations of the usage of relay-assisted VLC in vehicular applications are available in [68; 69]. In such cases, it has been experimentally demonstrated that a VLC link can be established with a VLC receiver that is not within the LoS by using an intermediate VLC node. The effect of vehicle misalignment could be also mitigated based on the integration of context and environment-adaptive techniques [47; 48]. In this case, an adaptable FOV can be used [41]. In [22], it has been demonstrated that the VLC receiver reception angle can be increased with the help of a proper optical lens. All these works prove that the research community is able to come up with solutions that will enable the use of the VLC technology in communication-based vehicle safety applications. Last but not least, it should be remembered that in addition to vehicle misalignment, the SNR at the VLC receiver level can also be influenced by weather phenomena that influences light passage (i.e., fog, rain, snowfall). Nevertheless, the research community has come up with solutions to reduce these effects. According to [70], snowfall is the most disruptive weather phenomena for VLC applications, reducing the communication distance by 20-80%. The effect of snowfall and of blizzards on vehicular VLC performances has been experimentally evaluated in [23; 24]. The results showed that even if the BER can be affected, the VLC link can be maintained as active, even in such unfriendly conditions. The solutions to such problems are generally based on an optical lens, improved signal processing techniques, which enable data recovery from low SNR signals, and FEC protocols to improve BER results in low SNR conditions. Therefore, as these issues have been already addressed by the research community, these aspects are only briefly mentioned in this manuscript. In these circumstances, one can see that the performances of automotive VLC systems are constantly improving. Therefore, the results of this article provide new evidence concerning the benefits associated with the use of the VLC technology in vehicular applications. Thus, in addition to an envisioned fast spreading possibility and a low cost generated by the wide distribution of the LED light sources, VLC technology can provide decent communication distances and a high reliability.