## 2 State of the Art in Optical Wireless Communications
### The Contribution of Communications Based on Visible Light in the Transmission of Information
The different types of LEDs and their properties depending on the area and field of application are shown in Table 2.  
This presentation covers only a brief discussion on the mode and exposure of LEDs, those converted to phosphorus (PC-LED) and LED multi-chip type (RGB LED). In the process of making VLC transmitters, RGB LEDs and PC LEDs are the most common and preferred because of the fact that they are also found in lighting fixtures having double utility for both transmission and lighting, capable of producing white light. In addition to these aspects, open environment applications are disturbed by the interference caused by natural light or other artificial light sources. In mitigating the effect of adverse conditions, the standard offers the convolutional coding (CC) variant superior to the Reed-Solomon coding, ideal for indoor tests. There is a multitude of tests and measurements in which schemes with separate RS and DC blocks were tested, subsequently improving performance by about 1 dB [65]. In a preliminary conclusion, the realization of fully functional applications in the direction of visible light communication systems dedicated to the external environment becomes a challenge and an extremely pressing point for the academic environment. According to the clarifications and research, we can highlight the fact that there is a lot of research that has been limited in how to apply this technology, especially the integration of mobile devices in direct communications with infrastructure [66]. According to Table 3, we highlighted the most important research in the analyzed direction. We can also see from Table 3 that all the efforts of the research teams were channeled over long transfer distances, speeds and stability. The external environment is a supreme test for most VLC systems and their stability because of increased dynamics and unpredictable conditions, starting from climatic factors to parasitic light. According to studies, we can use and outline an Android application that uses the entire front of mobile phones in the process of data management. This application needs some prioritization on the hardware components of the devices and the communication to be conducted according to the urgency of the messages. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Complexity** & **Performance** & **Bandwidth** & **Cost** & **Practicability** \\ \hline RGB LED & Moderate & 65 lm/W & 15–20 MHz & High & Lighting \\ PC-LED & Low & 140 lm/W & 5–3 MHz & Low & Lighting \\ OLED & High & 50 lm/W & \(\leq\)1 MHz & Lowest & Display \\ \(\mu\)-LED & Highest & - & \(\geq\)300 MHz & High & Biosensors \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The characteristics of LEDs depending on their type, performance, complexity, band and cost. Regarding the management of a road safety application, the aspects regarding the detection, transmission and reception of information can be carried out according to the color codes. These methods include ways of encoding and decoding, filtering and sampling signals. Notable and visible elements that come with the novelty are related to the usefulness of the application and the purpose of development, which is that a smartphone user who does not have distributed attention and travels a route without being informed about the traffic or pedestrian situation is informed regarding the obstacle or danger to which it is exposed.