# A Survey of Vehicular VLC Methodologies
## 4 Technical Challenges in Vehicular VLC and Solutions
### Sun and Artificial Light Sources  
Another critical challenge is the interference from artificial and natural light sources, which negatively affects the performance of vehicular VLC. This includes the ambient light from artificial light sources (such as fluorescent and incandescent lamps used for roads, traffic lights, infrastructure, and billboards) or natural light sources such as sunlight. In  
Figure 6: Impact of light sources, reflections, and weather in vehicular VLC. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Method** & **Refs.** & **Scenario** & **Comments** \\ \hline \multirow{3}{*}{**LoS**} & [69] & V2V & Proposed a headlight LoS path loss model \\ \cline{2-4}  & [74] & V2V & Submitted a taillight LoS loss model \\ \cline{2-4}  & [30] & V2V & Presented a LoS path loss model for an asymmetric headlight \\ \hline \multirow{3}{*}{**NLoS**} & [98; 99] & V2V & Described the effects of reflections on road surfaces \\ \cline{2-4}  & [96] & V2V & Reported on specular reflections on the road surface \\ \cline{2-4}  & [97] & V2V & Focused on the reflection from surrounding vehicles \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The effect of LoS, NLoS, and reflections on vehicular VLC. addition, the connection is hampered if there is a significant amount of radiation, defined as a situation where the maximum intensity of the light, both natural and artificial, is greater than the desired optical signal power. It is possible that the background radiation could be too intense in some scenarios (such as being in direct sunlight), leading to the receiver being entirely saturated. The electrical signal created by the photodiode's output is a direct current (DC), because the light from natural sources such as skyllights and sunlight cannot be modulated. The filter is often used on the receiving side, where it works on a low pass to reduce the effect of DC because it is utilized to connect with higher frequencies [23; 99]. The impact of light from the sun and artificial sources on vehicular VLC is depicted in Figure 6. Although the background radiation level causes noise, also known as shot noise, the shot noise is generated due to fluctuation in the photons arriving randomly at the PD [17]. The shot noise comes from solar radiation. In contrast, the variation in the shot noise is the result of artificial sources, which may cause significant communication problems during the day; thus, the noise generated is considered a negative factor for the performance of vehicle systems as, especially during sunset and sunrise, different angles of the sun can cause the deterioration and saturation of the photodiode [17; 23]. The sufficient bandwidth of the LEDs is likewise diminished when the weather is sunny. Approaches based on optics can also be used to deal with more problems of ambient light and generated disturbance noise. Methods concerning this have already been addressed. Utilizing highly directional receivers that can differentiate the wanted signal from the noise source is one potential approach to resolve the issue [23; 100]. Methods based on optics can also be used to deal with more problems of ambient light and generated disturbance noise. One approach that might be taken to resolve the issue is utilizing highly directional receivers that can separate the wanted signal from the noise source [71]. On the other hand, this may lower the system's tolerance for movement because it will have a narrower field of view (FOV) at the receiver. Additionally, the optical filtering of specific wavelengths, such as the blue filtering of light, has been proposed [101]. In contrast, when utilizing this method, in addition to the noise, significant signal strength may be lost on the wavelengths that are being blocked.