# A Review on LiFi Network Research: Open Issues, Applications and Future Directions
Inside an indoor area, data transmission through LiFi is indeed safer. The number of users who can connect to a LiFi AP is determined by the size of the attocell. LiFi signals appear once the AP's LED has been illuminated. The signals don't pass through walls. However, it is more challenging in the outdoor area because unauthorized users are more likely to detect LiFi transmitted signals without many constraints. Normally, the light bulb glows at a constant current supply, and a fast and stable electric current is required to generate stable optical outputs. LiFi only requires light, therefore it can be easily applied to any field where RF interaction is often difficult [17]. LED lights are used in LiFi to deliver good lighting since it uses the existing lighting infrastructure and provides illumination in indoor areas. In order to guarantee the general indoor illumination, a pre-requisite requirement of a minimum illuminance of 500 lux is needed, and the area optical power of LiFi APs is set to be 2.5 W/m2 [18]. Note that the measuring unit for illumination is lux [5; 10; 19; 20; 21; 22; 23; 24; 25; 26; 27]. LiFi technology has attracted high attention of the research community [6], and various research efforts on this technology have constantly been growing [6]. This technology is best known for its various importance and contributions over other existing technologies (i.e., Wi-Fi, Bluetooth, and RF identification) [6], which include high data transmission rates [9], fast speed [26], safety [5], availability [4], efficiency [28], security [29] and low cost [30]. The integration of LiFi in every light source creates an opportunity to shift ubiquitous light to the connected objects. Therefore, boosting its potentials and expansion in tremendous ways [6]. Extensive research on this technology and its various potentials will yield remarkable findings from the perspectives of science and academia and from various interested parties that have the commercial ability to integrate this technology in their respective domains. Organizations also will benefit from the full potential, and it will pave the way for new communications in the future. Thus, it is a very important topic that receives considerable attention that has served as an important motivating factor for this paper. This paper provides a comprehensive review of this technology from various aspects, and it addresses its unique features, research trends, and open issues to be pursued to further contribute towards the empowerment and deployment of this technology. The contributions of this study can be summarized as follows: (I) a detailed literature review and a multi-aspect classification is introduced. (II) Identification of the most important features of the architectural component of LiFi network systems. (III) Detailed discussion on the advantages and disadvantages of this technology. (IV) A comprehensive comparison between LiFi and other technologies. (V) discussion of multi-user access in LiFi networks. (VI) discussions on the most significant scientific challenges and open issues for LiFi and finally a comprehensive discussion of the highly utilized area of LiFi applications. This paper is organized into ten sections. Section 2 describes the review protocol used for the respective research methods, literature sources, and filtering steps in selecting research articles. In Section 3, the classification and statistical analysis results from the final set of reviewed articles are also outlined. Section 4 presents LiFi applications. Section 5 presents the components and architecture of the LiFi system. Section 6 discusses the advantages and disadvantages of LiFi in detail. Section 7 compares the main differences between LiFi and Wi-Fi. Section 8 explains the types of multi-user access used in LiFi. Section 9 presents the open issues and discussion. Section 10 presents the limitations and new future research directions. Section 10 concludes this study.