# A Survey of Vehicular VLC Methodologies
## 2 Visible Light Communication
### VLC Challenges  
Despite the many advantages that VLC systems possess, they contain some defects. Most defects date back to the beginning of VLC technology and may be bypassed when the technology is fully developed. Another reason is the way light is used and its characteristics. It is not easy to eliminate these, but their impact can be mitigated, and communication can be adapted to the circumstances. * Line-of-Sight (LoS) Blockage Line-of-sight (LoS) connection is often considered necessary for VLC systems, as it raises system efficiency and reduces multi-path distortion. The required LoS state can be considered beneficial in some cases. On the other hand, other applications see this as a significant drawback because the requirement for LoS restricts motion. In some cases, visible light is a considerable drawback when the barrier prevents communication from progressing when no other path is accessible [43; 52; 53]. Furthermore, communication links can be provided while using intelligent reflecting surface (RIS) technology, digital twin technology [54], and multi-hop relaying techniques [55]. * Limited Transmission Range VLC technology has a greater bandwidth than radio frequency. However, the transmission range of VLC is smaller than RF. The transmission range is increased by first improving the characteristics of VLC transmitters and receivers; secondly, by increasing the transmitting power by using a more focused and directed light beam; and thirdly, by expanding the communication bandwidth on the emitter side or increasing the field of view on the receiver side; however, this can increase interference. In all of the above cases, VLC communication is much shorter than radio frequency communication [56; 57; 58; 59]. On the other hand, the communication range is improved by using several techniques that increase the signal-to-noise ratio (SNR) by using an optical lens or a narrow FoV receiver; also, by using different filtering techniques or through the multi-hop connection, the connection capacity of VLC systems can be significantly increased. * Interference and Noise VLC is affected by light from other sources, including artificial sources such as fluorescent and incandescent light; these usually produce low-frequency noise, which is eliminated using high-frequency filters. On the other hand, VLC systems are affected by sunlight, where sunlight creates unmodulated light that is a direct electrical current having a strong effect on the receiver [19; 60]. The received signal is improved, and noise is removed using capacitive DC filters. Still, high-density optical noise hinders communication and saturates the receiver. Moreover, the receiver's low field of view and optical and electrical filters can eliminate unwanted noise. Although these technologies mitigate the impact of interference, the VLC connection remains affected by high noise levels. VLC Application  
VLC technology has gained popularity in various applications due to its appealing features, including high bandwidth, low power consumption, unlicensed channels, and absence of health risks. It can serve as a standalone solution or complement radio frequency communication to achieve high-speed and efficient data transmission. VLC applications can be classified into three main categories based on their respective areas of application: indoor, outdoor, and underwater. Indoor VLC has found widespread use in numerous applications, some of which are:  
* Li-Fi  
One prominent application that has emerged for VLC's high-speed capabilities is Li-Fi, also known as \"optical Wi-Fi\" or \"light fidelity.\" The term Li-Fi was coined by Professor [PERSON] in 2011, leading to the establishment of the Li-Fi consortium to harness the technology's rapid development and immense potential [11,13]. Li-Fi functions as a bidirectional system similar to conventional Wi-Fi, but with the advantage of leveraging VLC's extensive bandwidth.