# Optical-OFDM VLC System: Peak-to-Average Power Ratio Enhancement and Performance Evaluation
## 4 PAPR Reduction Methodology and Proposed Model
### Proposed PAPR Reduction System
At a BER of \(10^{-4}\), ADO-OFDM demonstrated lower \(\rm E_{b}/N_{O}\) for both the 4- and 16-QAM schemes at a 7 dB DC bias value compared to the performance at the same modulation schemes but with 10 and 13 dB DC bias values. However, \(\rm E_{b}/N_{O}\) at 10 dB and 13 dB DC bias values for other modulation schemes provided lower values comparable to \(\rm E_{b}/N_{O}\) at a 7 dB DC bias value. ADO-OFDM with a 13 dB DC bias value for 1024-QAM exhibited a lower \(\rm E_{b}/N_{O}\) compared to ADO-OFDM operating at a 10 dB DC bias value for the same 1024-QAM modulation. Otherwise, for other modulation schemes, ADO-OFDM with a 10 dB DC bias value showed an \(\rm E_{b}/N_{O}\) that is approximately 2.6 lower compared to ADO-OFDM operating at a 13 dB DC bias value. The numerical results for this scheme are presented in Table 6, showcasing various DC bias levels with different modulation orders. At a CCDF of \(10^{-3}\), the PAPR values of ADO-OFDM operating at a 13 dB DC bias level for various modulation orders showed lower values compared to ADO-OFDM operating at 10 and 7 dB DC bias values, as outlined in Figure 14b. Table 6 illustrates the comparison of PAPR0 values for different DC bias levels in ADO-OFDM across various modulation orders. The average PAPR0 values were 7.032 dB, 8.4706 dB, and 10.278 dB at the 13 dB, 10 dB, and 7 dB DC bias values, respectively. Based on the evaluated numerical data for DCO and ADO-OFDM, it was observed that the PAPR0 of ADO-OFDM was higher than that of DCO-OFDM at various DC bias levels across different modulation orders. It indicates that the dynamic range of the PAPR0 for DCO-OFDM was lower than that of ADO-OFDM for various DC bias levels and modulation orders by approximately an average value equal to 0.8 dB. Figure 13: Performance of FLIP-OFDM for (**a**) BER and (**b**) PAPR. ### Exploring BER and PAPR for ASCO-OFDM

The evaluated \(\text{E}_{\text{b}}/\text{N}_{\text{o}}\) values for ASCO-OFDM decreased as the modulation order increased, showing a decreasing trend by an approximate average of 4.2, as depicted in Figure 14(a). The corresponding numerical values for this evaluation are detailed in Table 6, specifically at a BER of \(10^{-4}\). As previously mentioned, while the SE of ASCO-OFDM surpassed that of FLIP and ACO-OFDM, the \(\text{E}_{\text{b}}/\text{N}_{\text{o}}\) evaluation values for both FLIP and ACO-OFDM were lower than those of ASCO-OFDM across different modulation orders, with an approximate difference of 2.1 dB at a BER of \(10^{-4}\). ASCO-OFDM's CCDF is represented in Figure 14(b). At a CCDF of \(10^{-3}\), the PAPR0 values for ASCO-OFDM operating with 64-QAM and 256-QAM were approximately equal, measuring around 15.5 dB. The PAPR0 values for 4-QAM, 16-QAM, and 1024-QAM were recorded as 15.15 dB, 15.03 dB, and 15.32 dB, respectively. With various modulation orders, the average PAPR0 value of ASCO-OFDM was 15.306 dB. The ASCO-OFDM not only exhibited significantly higher SE values compared to FLIP and ACO-OFDM but also showcased lower PAPR values in contrast to both FLIP and ACO-OFDM. The

Figure 14: Performance of ADO-OFDM for (**a**) BER and (**b**) PAPR. Figure 15: Performance of ASCO-OFDM for (**a**) BER and (**b**) PAPR. approximate average reduction values were 1.174 dB for ACO-OFDM and 1.38 dB for FLIP-OFDM, respectively. ### Exploring BER and PAPR for LACO-OFDM

As previously detailed in Section 3, the SE of LACO-OFDM is influenced upon the number of layers employed in its construction. Consequently, in this section, we aimed to evaluate the BER and PAPR for LACO-OFDM across various construction layers and different modulation orders. In Figure (a)a, the BER performance of two-layer LACO-OFDM approach, denoted as LACO\({}_{2}\)-OFDM, is examined across different modulation orders. The numerical results indicate that the behavior of LACO\({}_{2}\)-OFDM was superior to that of ASCO-OFDM, despite both having the same SE.