# A Brief Overview of Energy Efficiency Resources in Emerging Wireless Communication Systems
## 4 Optical Wireless Communication Schemes  
In 2017, a general standard was researched and formulated to develop new products in VLC-IEEE 802.15.7. They considered three separate VLC system applications: infrastructure, vehicle, and cellular applications. The standard aims to specify the speed of communication, modulation and error correction schemes, providing immunity against electromagnetic interference, providing connection to several hundred THz bands, etc., [70, 71, 72]. It showed high feature bandwidth, making VLC an attractive technique for future communication and a promising field for further research. It was investigated that combining RF and VLC would be a better communication scheme as it is better to support RF with VLC systems than just eliminating RF. Work on the concept described had been earlier carried out in 2016. The authors in [73] carried out an optimized energy-efficient scheme that incorporated both an RF and a VLC system. A VLC system model was proposed with a single-user transmitter and receiver. The derivation of algorithms obtained allocations for the power and bandwidth of the system. Throughput improvement of the system and energy efficiency optimization was achieved. None-Line-of-Sight VLC transmissions were not considered; therefore, their transmission was unsuccessful. One factor that contributed to the transmission failure was that the network and the varying position of the users were not analyzed. In [74], the authors proposed a system analyzing the relationship between the position of the network and users. An amorphous structure was used instead of the normal conventional structure. A proposed system-level energy-efficient maximization algorithm for the initial algorithms was simulated to prove that it had a higher energy efficiency per user for different angles of its field of view. Only the transmission power was considered as the source of power consumption. An open issue that was not addressed was how the VLC energy consumption is measured. Other sources of power consumption included signal processing costs, backhaul power consumption, etc. Additionally, the proposed algorithms were strictly for indoor cases and did not permit the mobility of users. Unlike [74], which used an amorphous setup, the work in [75] used a user-centric design philosophy to show a concept whereby VLC was integrated into the radio frequency (RF) heterogeneous network environment. It reviewed answers to problems like multi-user signal processing, scheduling and resource management. The survey in this paper proposed a system-level VLC network substituting network-centric design for a user-centric design philosophy, taking significant cognizance of minimizing interference. Research in 2020 [76] showed the connection between user association performance in a visible light cell where the user association was studied in a multicell non-orthogonal multiple access (NOMA) VLC network. The research was carried out because of the difficulty in obtaining optimal strategies for how users in a multicell NOMA-VLC network relate, which led to the study of their relationship using the proximity access principle. [PERSON]'s mathematical model theory was used to depict the basic system model. In order to prove the theoretical analysis, the MATLAB program software and the Monte Carlo simulation methods were utilized. The simulation results showed that the Virtual Power Purchase Agreements (VPPA) improved rate response based on sufficient conditions than the proximity access principle. The authors did not include the study of how a multi-cell NOMA-VLC network allots power and assembles its users. The authors in the article [77] proposed a full-duplex VLC system with several users who can handle different devices. The system was separated into downlink and uplink sections. Other modulation schemes were employed in the system. The cost and power consumption analysis were carried out concerning the data throughput.