# A Survey of Vehicular VLC Methodologies
## 1 Introduction
 \\ \hline \multicolumn{1}{c}{Superiority of VLC} & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline \multirow{4}{*}{Architecture} & Transmitter & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \cline{2-11}  & Receiver & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \cline{2-11}  & Channel & & & & & & & & & & \\ modeling & & & & & & & & & & & \\ \hline \multirow{4}{*}{Modulation} & OOK, PWM, PPM & \(\surd\) & & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \cline{2-11}  & OFDM & & & \(\surd\) & & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline \multirow{4}{*}{Challenges} & LoS & \(\surd\) & & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \cline{2-11}  & Noise and & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \cline{2-11}  & Interfer- & \(\surd\) & \(\surd\) & & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \cline{2-11}  & One & Mobility & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline \multirow{4}{*}{VLC Application} & Indoor & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \cline{2-11}  & Positioning & \(\surd\) & & \(\surd\) & & & \(\surd\) & & \(\surd\) & \(\surd\) \\ \cline{2-11}  & Smart & & & & & & & & & & \\ cities & & & & & & & & & & & \\  
unlike in indoor applications. Realistic channel models are the first step to solving most of these challenges in vehicular VLC systems. Earlier results have focused on indoor channel modeling, which does not apply to vehicular VLC systems with inherently different characteristics. For example, earlier works assumed the ideal Lambertian model for vehicular light sources, which fails to match the illumination characteristics of automotive headlights, taillights, traffic lights, and streetlights with their asymmetrical intensity distributions [30; 31; 32; 33; 34; 35; 36; 37; 38; 39]. The effects of road reflectance, road type, weather conditions, the orientation of the user/vehicle equipment and infrastructure, receiver aperture size, and sunlight might strongly affect the link performance of vehicular VLC systems. Therefore, it is urgently necessary to investigate this research area and its unique uses in traffic safety based on realistic channel models. This paper presents an in-depth and comprehensive survey of vehicular VLC systems, covering various critical aspects including a technology overview, system components, signal models, potential applications, environmental challenges, and emerging research areas. It investigates recent advancements in realistic channel models, explores different types of vehicular VLC links, and introduces novel techniques such as reconfigurable intelligent surfaces (RISs), multi-hop relaying, and digital twins. The technology overview section provides insights into the fundamental principles, operation, and advantages of VLC technology, along with an examination of essential system components such as light sources, receivers, photodetectors, and modulators. Signal modeling and indoor scenarios are thoroughly explored, with a focus on understanding the main signal models used in VLC and the unique considerations for indoor environments compared to outdoor settings. The potential applications of vehicular VLC are examined, highlighting its transformative impact on the automotive industry and intelligent transportation systems, including lane changing assistance, intersection assistance, platooning, and V2V/V2I communications. Environmental challenges are addressed, investigating factors such as road reflections, interference, and weather conditions, emphasizing the importance of mitigating these challenges for robust communication.