# Optical-OFDM VLC System: Peak-to-Average Power Ratio Enhancement and Performance Evaluation
## 3 Assessment Criteria Employed to Judge the Effectiveness of MCM Approaches
### Data Arrangement and Spectral Efficiency
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**MCM TECHNIQUE** & **Spectral Efficiency Formula** & **4-QAM** & **16-QAM** & **64-QAM** & **256-QAM** & **1024-QAM** \\ \hline DCO-OFDM & \(\frac{log_{2}M}{1+\frac{2}{N}}\) & 1.9961 & 3.9922 & 5.9883 & 7.9844 & 9.9805 \\ \hline ACO-OFDM & \(\frac{log_{2}M}{1+\frac{2}{N}}\) & 0.9981 & 1.9961 & 2.9942 & 3.9922 & 4.9903 \\ \hline FLIP-OFDM & \(\frac{log_{2}M}{1+\frac{2}{N}}\) & 0.9981 & 1.9961 & 2.9942 & 3.9922 & 4.9903 \\ \hline ASCO-OFDM & \(\frac{log_{2}M_{odd}}{1+\frac{2}{N}}+\frac{log_{2}M_{odd}}{4+\frac{log_{2}M_{odd }}{4}}\) & 1.4971 & 2.9942 & 4.4912 & 5.9883 & 7.4854 \\ \hline ADO-OFDM & \(\frac{log_{2}M_{odd}}{1+\frac{2}{N}}\) & 1.9961 & 3.9922 & 5.9883 & 7.9844 & 9.9805 \\ \hline LACO\_2-OFDM & \(\frac{log_{2}M_{odd}}{1+\frac{2}{N}}\) & 1.4971 & 2.9942 & 4.4912 & 5.9883 & 7.4854 \\ \hline LACO\_3-OFDM & \(\frac{log_{2}M_{odd}}{1+\frac{2}{N}}\) & \(\frac{log_{2}M_{odd}}{3+\frac{2}{N}}\) & 1.7466 & 3.4932 & 5.2398 & 6.9864 & 8.7329 \\ \hline LACO\_4-OFDM & \(\frac{log_{2}M_{odd}}{1+\frac{2}{N}}+\frac{log_{2}M_{odd}}{4+\frac{log_{2}M_{odd }}{4}}+\frac{log_{2}M_{odd}}{4}\) & 1.8713 & 3.7427 & 5.6140 & 7.4854 & 9.3567 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Spectral efficiency formula for various O-OFDM approaches and the evaluation values (bits/sec/Hz) for various constellation sizes at an FFT/IFFT size of 1024 [2,43]. In particular, Figure 9 and Table 2 illustrate the SE of the previously mentioned methods at M equaling 16-QAM. This figure illustrates that as the FFT/IFFT size increases, there comes a point where the SE does not exhibit a significant improvement. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**MCM TECHNIQUE** & **N = 8** & **N = 16** & **N = 32** & **N = 64** & **N = 128** & **N = 256** & **N = 512** & **N = 1024** & **N = 2048** & **N = 4096** \\ \hline DCO & 3.2 & 3.5556 & 3.7647 & 3.8788 & 3.9385 & 3.9690 & 3.9844 & 3.9922 & 3.9961 & 3.9980 \\ \hline ACO & 1.6 & 1.7778 & 1.8824 & 1.9394 & 1.9692 & 1.9845 & 1.9922 & 1.9961 & 1.9980 & 1.9990 \\ \hline FLIP & 1.6 & 1.7778 & 1.8824 & 1.9394 & 1.9692 & 1.9845 & 1.9922 & 1.9961 & 1.9980 & 1.9990 \\ \hline ASCO & 2.4 & 2.6667 & 2.8235 & 2.9091 & 2.9538 & 2.9767 & 2.9883 & 2.9942 & 2.9971 & 2.9985 \\ \hline ADO & 3.2 & 3.5556 & 3.7647 & 3.8788 & 3.9385 & 3.9690 & 3.9844 & 3.9922 & 3.9961 & 3.9980 \\ \hline LACO\_2 & 2.4 & 2.6667 & 2.8235 & 2.9091 & 2.9538 & 2.9767 & 2.9883 & 2.9942 & 2.9971 & 2.9985 \\ \hline LACO\_3 & 2.8 & 3.1111 & 3.2941 & 3.3939 & 3.4462 & 3.4729 & 3.4864 & 3.4932 & 3.4966 & 3.4983 \\ \hline LACO\_4 & 3 & 3.3333 & 3.5294 & 3.6364 & 3.6923 & 3.7209 & 3.7354 & 3.7427 & 3.7463 & 3.7482 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The assessment of spectral efficiency (bits/sec/Hz) values across multiple O-OFDM approaches for varying FFT sizes using a 16-QAM modulation scheme. Figure 8: The fluctuations in spectral efficiency regarding changes in modulation order were examined while maintaining a fixed FFT/IFFT size of 1024 for various O-OFDM schemes. Figure 9: The fluctuations in spectral efficiency are examined concerning changes in FFT/IFFT size while maintaining a modulation scheme of 16-QAM for various O-OFDM schemes.