# Optical-OFDM VLC System: Peak-to-Average Power Ratio Enhancement and Performance Evaluation
## 4 PAPR Reduction Methodology and Proposed Model
### Proposed PAPR Reduction System
The E\({}_{b}\)/N\({}_{0}\) values at a BER of \(10^{-4}\) for LACO\({}_{2}\)-OFDM were, on average, approximately 1.7 dB lower than ASCO-OFDM across different modulation orders. However, the E\({}_{b}\)/N\({}_{0}\) values for LACO\({}_{2}\)-OFDM were, on average, approximately 0.4 dB higher than FLIP and ACO-OFDM across different modulation orders. Figure (b)b examines the CCDF performance of LACO\({}_{2}\)-OFDM across various modulation orders. With the modulation order changing, a minor change was observed in the PAPR0. At a CCDF of \(10^{-3}\), the average PAPR0 value of LACO\({}_{2}\)-OFDM was the same as that of ASCO-OFDM, approximately equaling 15.3 dB. The PAPR0 values for LACO\({}_{2}\)-OFDM using 64-QAM and 256-QAM were approximately similar to those provided by ASCO-OFDM. The performance of the BER for the three-layer LACO-OFDM approach, referred to as LACO\({}_{3}\)-OFDM, is examined across different modulation orders in Figure (a)a. The SE of LACO\({}_{3}\)-OFDM was higher than that of ASCO and LACO\({}_{2}\)-OFDM. However, the E\({}_{b}\)/N\({}_{0}\) values of LACO\({}_{3}\)-OFDM at a BER of \(10^{-4}\) were lower than those of ASCO-OFDM by an approximate average value of 0.544 dB but higher than those of FLIP, LACO\({}_{2}\)-OFDM, and ACO-OFDM by an approximate average value of 1.168 dB, 1.584 dB and 1.616 dB, respectively. Figure 16: Performance of the two-layer LACO-OFDM for (a) BER and (b) PAPR. Figure 17b explores the CCDF evaluation of \(\text{LACO}_{3}\)-OFDM for different modulation orders. A slight change in the PAPR0 was noticed as the modulation order changed. At a CCDF of \(10^{-3}\), the PAPR0 values of \(\text{LACO}_{3}\)-OFDM with 16, 64, and 1024-QAM were approximately equal. The average PAPR0 value of \(\text{LACO}_{3}\)-OFDM was approximately 0.813 dB lower than ASCO-OFDM, 1.987 dB lower than ACO-OFDM, 2.195 dB lower than FLIP-OFDM, and 0.827 dB lower than \(\text{LACO}_{2}\)-OFDM. The evaluated PAPR0 results for \(\text{LACO}_{3}\)-OFDM are presented in Table 6, showcasing the performance across various modulation orders. Following the assessment of \(\text{LACO}_{2}\)-OFDM and \(\text{LACO}_{3}\)-OFDM, we moved forward to assess the LACO-OFDM approach with four layers, known as \(\text{LACO}_{4}\)-OFDM. Figure 18a displays the BER performance of \(\text{LACO}_{4}\)-OFDM. The evaluation was conducted across varying modulation orders, specifically within the \(\text{LACO}_{4}\)-OFDM framework. The numerical results from the evaluation indicate that the BER performance of \(\text{LACO}_{4}\)-OFDM was lower compared to \(\text{LACO}_{3}\), \(\text{LACO}_{2}\), ASCO, FLIP, and ACO-OFDM across various modulation orders. The average \(\text{E}_{b}\)/\(\text{N}_{\text{o}}\) value for \(\text{LACO}_{4}\)-OFDM at a BER of \(10^{-4}\) exceeded that of \(\text{LACO}_{3}\), \(\text{LACO}_{2}\), ASCO, FLIP, and ACO-OFDM by approximately 0.824 dB, 10,992 dB, 0.28 dB, 2.408 dB, and 2.44 dB, respectively. Figure 17: Performance of the three-layer LACO-OFDM for (**a**) BER and (**b**) PAPR. Figure 18: Performance of the four-layer LACO-OFDM for (**a**) BER and (**b**) PAPR. As we evaluated the BER performance of \(\mathrm{LACO_{4}}\)-OFDM, we also assessed the CCDF, which is illustrated in Figure 18b. At a CCDF of \(10^{-3}\), the PAPR0 values for 4, 256, and 1024-QAM modulation orders were approximately equal. The PAPR performance of \(\mathrm{LACO_{4}}\)-OFDM was better compared to \(\mathrm{LACO_{3}}\), \(\mathrm{LACO_{2}}\), \(\mathrm{ASCO}\), FLIP, and ACO-OFDM across various modulation orders. At a CCDF of \(10^{-3}\), the average PAPR0 value for \(\mathrm{LACO_{4}}\)-OFDM was less than that of \(\mathrm{LACO_{3}}\), \(\mathrm{LACO_{2}}\), \(\mathrm{ASCO}\), FLIP, and ACO-OFDM by around 0.6796 dB, 1.5066 dB, 1.4926 dB, 2.666 dB, and 2.8746 dB, correspondingly.