# A Brief Overview of Energy Efficiency Resources in Emerging Wireless Communication Systems
## 4 Optical Wireless Communication Schemes
\begin{table}
\begin{tabular}{p{42.7 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**S/N** & **Author** & **FewsonMain Contribution** & **Results** & **Limitation/Dawback** \\ \hline
1 & [PERSON]. [PERSON] et al., 2010 & The work analyzed the impact of OFDM in an OWC system showing the relationship between the modulation and and the degree of SNR. & System quality depend on the order of the modulation and how the LEBs were clipped. & The system needs improvement because it has a low data rate. \\ \hline
2 & [PERSON]. [PERSON] et al., 2011 [86] & The work introduced the use of spatial modulation in OWC. & It provided a better data rate than previous schemes. & More work will needs to be done on the technique. \\ \hline
3 & [PERSON] et al., 2016 [74] & An amorphous setup to provide spectral efficiency in a VLC network. & Higher energy efficiency per user was obtained using a cells compared to the conventional cell formation for the different practical field of views (OFVs) angles. & Strictly for indoor cases and does not permit user mobility. Furthermore, the non-linear clipping for the different practical field of views is distortion effect for the capacity expression of OVOVM’s angles. & Strictly for indoor cases and does not permit user mobility. Furthermore, the non-linear clipping for the different practical field of views is distortion effect for the capacity expression of DO-OFDM was not considered. \\ \hline
4 & [PERSON] et al., 2016 [77] & Derived and formulated allocation algorithms to maximize the energy efficiency of a heterogeneous network that had both RF and VLC. & It was shown that the proposed network would produce more benefits than using just an RF network. & None-of-sight VLC transmission was not considered, therefore, their transmission was unsuccessful. \\ \hline
5 & [PERSON], 2017 [70] & Survey of VLC standardization, modulation, and techniques, potentially applications, architecture, and open research. & Numerous factors like high bandwidth have made & It did not provide a feasible model for an energy-efficient VLC system. \\ \hline
6 & [PERSON] et al., 2017 [77] & The work utilized ACO-OFDM for downlink transmission and COK and PAM-COK for the proposition of multiple connected VLC networks. & The system’s performancemet data transmission requirements for indoor environments. However, it had a high altitude but lower bacterial cost, making a task-efficient. It was also power-efficient. & It had a low data rate \\ \hline
7 & [PERSON] et al., 2017 [70]. & The work proposed an LED index modulation method for MIMO-OFDM based VLC system. & Using spatial multiplexing and LEID index modulation, spectrum efficiency losses were estimated by the frequency domain shaping in four transmit LEDs \\ \hline
8 & [PERSON] et al., 2018 [79]. & The work proposed a dense VLC system that serves several users simultaneously using a cell-free massive multiple input multiple output (CFM-MIMO) system. & Dense VLC enhanced the rate at which data were transmitted and the power efficiency compared to traditional means, a heuristic model was designed to form transmitters of their placement is not adequately reconstructed. \\ \hline
9 & [PERSON], [PERSON], [PERSON] et al., 2018 [71] & Analysed LED domain positioning for a MIMO-OFDM as a multiple of four transmit LEDs, formulating as scheme that had a reduced detection complexity compared with the core in [79] & The scheme obtained was better than the one in [79] & It can also be applied to a setup with multiple four transmit LEDs \\ \hline \end{tabular}
\end{table} 
Table 3: Summary of work utilizing different optical wireless communication modulation schemes.