## 1 Introduction
The complexity of dealing with these problems becomes even more challenging because they have antagonistic characteristics, and establishing the optimal tradeoff between them is rather difficult. In fact, sacrificing the mobility of vehicular VLC systems by reducing the VLC receiver's FoV was, for a long period, the handiest solution to improve the noise resistance [12]. Thus, in the early years, long-range vehicular VLC prototypes sometimes had FoVs as narrow as 0.4-3\({}^{\circ}\)[31; 32]. Later on, as the design of VLC receivers improved, better tradeoff solutions were integrated. Thus, today's vehicular VLC receivers commonly have \(\pm\)20\({}^{\circ}\) FoVs [21; 24; 25; 26], while sometimes reaching \(\pm\)50\({}^{\circ}\)[25]. Nevertheless, wide FoV VLC receivers are not able to maintain an active link under sunlight conditions, or they may only be able to provide limited communication ranges. For example, the solutions presented in [23; 25] were able to provide long-range communication only in indirect sunlight conditions, with the VLC receiver demonstrating an optical irradiance of up to 5000 \(\upmu\)W/cm\({}^{2}\). This demonstrates that, as the communication range increases and the SNR decreases, certain reliability issues might appear, pointing out that additional research efforts are required. As previously mentioned, in the initial development stage, this problem was addressed mostly by reducing the VLC receiver's FoV. This method takes advantage of VLC mandatory line-of-sight (LoS) conditions. Thus, as a VLC receiver uses a photodiode (PD) to transform light into an electrical signal, whereas a PD will generate an electrical current directly proportional to the incident light, it is obvious that less optical noise will reach the PD's surface when the FoV is reduced. Additionally, when the FoV is reduced, part of the optical noise source is spatially isolated. This leads to lower chances of photodiode saturation and also limits the effects of light-introduced shot noise. Although rather primitive, this method is very effective at enhancing the SNR and improving the performance of VLC receivers. Nevertheless, as vehicular VLC is highly dynamic, the narrow FoV can lead to situations in which the VLC transmitter goes outside the FoV, interrupting the link. Consequently, additional optical noise-mitigation techniques are required. Another very effective solution is represented by the use of optical filters [33; 34; 35]. Optical filters allow the passage of the desired wavelengths while attenuating other wavelengths. Thus, for applications that involve the use of the entire visible light spectrum, infrared (IR) reject filters are commonly used [19; 23], whereas for applications that require only certain colors, narrow-band-pass optical filters are applied. In most cases, such filters have a 40 nm band-pass region [25; 26], and the characteristics of the filter are selected in accordance with the VLC transmitter's optical characteristics. The use of optical filters can eliminate more than 50% of the optical noise, significantly improving the SNR. The obvious problem with this approach is that, in a traffic scenario, the VLC receiver can only detect one wavelength of light sources, such as the red light from a vehicle's taillight, thereby disregarding other light colors, such as the green or yellow emitted by traffic lights. Therefore, IR-reject optical filters represent an efficient tradeoff solution. As we move forward in the VLC receiver's architecture, the optical noise resilience can be improved with the help of an adequately designed transimpedance circuit. For example, in [19], a new logarithmic transimpedance circuit design was proposed and experimentally evaluated. The experimental results showed that such a design prevents saturation under in strong optical-noise conditions and significantly improves the dynamic range.