## 1 Introduction
### Optical Interferences Associated Issues and Solutions  
Whether we like it or not, autonomous vehicles will become a reality in the near future as part of the Intelligent Transportation System and Smart City concepts [24]. This solution is based on the fact that such vehicles have the potential to provide enhanced safety and improved traffic efficiency. In this new vehicular paradigm, wireless communications will play one of the leading roles, as they have the potential to provide the vehicle with much more information than any other on-vehicle sensor. Moreover, wireless communication technologies will enable a vehicle to have information concerning an event that occurred few kilometers away from its current location. Nevertheless, there are several wireless access technologies that compete in order to have their market share in this new emerging industry. Currently, IEEE 802.11p and short-range Cellular-V2X are some of the most advanced technologies in this domain, whereas other technologies, such as VLC, millimeter Waves, or 5G technologies are eager to prove their potential in this field [25]. The usage of VLC technology in outdoor applications implies significantly different conditions compared to its usage in indoor applications. Thus, in indoor applications, the VLC emitter is assumed to be the primary source of light, and so high SNRs that can go up to 20-50 dB are expected [26]. In these circumstances, it is assumed that the indoor lighting system is used in VLC, and so perturbations from artificial lighting are not implicated. So, the high SNR indoor conditions enable the usage of the VLC technology in high data rate applications, coined today as Li-Fi technology [26; 27], high precision indoor location [28; 29; 30], Internet of Things (IoT) services [31], location based informational systems [32], smartphone applications [33], and future 5G/6G technologies [26; 34]. On the other hand, outdoor applications are affected by numerous sources of artificial light. Incandescent lighting sources and fluorescent lighting sources introduce a strong 100 Hz component with harmonics that can go up to 2 kHz, respectively 20 kHz. Moreover, fluorescent lighting sources with electronic ballast introduce harmonics that can go up to few MHz [2]. In addition to the multitude of artificial lighting sources, the sun introduces a strong light component that can go up to 100.000 lux. Based on the existing outdoor VLC literature [2; 16; 35; 36] and on the arguments presented in Section 1, strong sunlight is considered the most important source of noise in outdoor VLC applications. The effects of the sunlight are influenced by location and time, with the effects on different spectral bands being modified from sunrise to sunset [16]. An attempt to develop an automotive VLC system designed to work in direct sun exposure is presented in [37]. In this case, the sensibility of the transimpedance circuit was established in order to prevent saturation of the photosensitive element in direct sun exposure (i.e., 100.000 lux). This approach enabled the communication in strong sunlight conditions, but reduced the reliable communication link to only 10-12 m. A 50 m communication distance has been reported in [20]. However, in this case, the experimental evaluation is performed in outdoor conditions without the sunlight being directly incident on the VLC receiver. In [38], the effect of the optical noise is reduced with the help of a spread spectrum modulation. Nevertheless, the spread spectrum techniques are helpful only if the photosensitive element is not saturated, pointing out that solutions to prevent the saturation of the automotive VLC receivers are still required. Probably the most impressive results concerning the VLC usage in strong lighting conditions are found in [16; 36]. According to the findings of these papers [16; 36], high data rate communications that can go up to 1 Gb/s are possible even in direct sunlight exposure.