# Optical-OFDM VLC System: Peak-to-Average Power Ratio Enhancement and Performance Evaluation
## 4 PAPR Reduction Methodology and Proposed Model
### Proposed PAPR Reduction System
E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) is computed by subtracting the E\({}_{\text{b}}\)/N\({}_{\text{0}}\) value of the proposed methodology from the conventional value at a BER of \(10^{-4}\). It is essential to note that there are three scenarios for the E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\), value: When E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) is less than zero, the system's BER performance is enhanced as it requires less energy to achieve the same BER. When E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) equals zero, there is no diminish in the BER performance. When E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) is greater than zero, the BER performance deteriorates because more energy is needed to attain the same BER. Figure 11:4

In this assessment, a comprehensive analysis of the numerical outcomes was specifically conducted for the 16-QAM technique, as depicted in Figure 20 and Figure 11:5 Figure 20 depicts the influence of employing VLM precoding methodology on the BER performance across various MCM approaches. At a BER of \(10^{-4}\), the traditional ACO-OFDM E\({}_{\text{b}}\)/N\({}_{\text{0}}\) value stood at 15.23 dB. Upon applying the VLM technique, there was no noticeable change in the E\({}_{\text{b}}\)/N\({}_{\text{0}}\) value. Likewise, in the case of the FLIP-OFDM approach, employing the VLM precoding technique did not yield significant alterations in the E\({}_{\text{b}}\)/N\({}_{\text{0}}\) value; the values remained relatively unchanged. The E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) for these two approaches was approximately zero, indicating no degradation in the BER performance for the FLIP-OFDM technique after the VLM precoding methodology was implemented. The DC bias level significantly impacted the BER performance of DCO-OFDM and ADO-OFDM. At a 7 dB DC bias, these approaches could not be assessed at a BER of \(10^{-4}\) after applying the VLM precoding technique but could be evaluated at a BER of \(10^{-3}\). The E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) at a BER of \(10^{-3}\) equalled 1 dB and 1.7 dB for ADO and DCO-OFDM, respectively. With a 10 dB DC bias, the E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) for DCO-OFDM was \(-0.6\) dB, indicating a slight improvement in the BER performance of this approach. Conversely, E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) for ADO-OFDM at a 10 dB DC bias was 0.1 dB, signifying a slight degradation in the BER performance of this approach. At a 13 dB DC bias, the E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) for ADO and DCO-OFDM equalled 0.06 dB and 0.09 dB, almost approaching zero, suggesting no substantial degradation in the BER performance for these two approaches. For ASCO, LACO\({}_{\text{2}}\), LACO\({}_{\text{3}}\), and LACO\({}_{\text{4}}\)-OFDM, the E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\) values were 0.1 dB, 0.45 dB, 0.57 dB, and 0.6 dB, respectively. This indicates a slight degradation in the BER performance of these approaches. However, if the PAPR reduction is considerably greater than this degradation factor, this level of degradation might be acceptable. Figure 19(b) demonstrates that at a CCDF of \(10^{-3}\), the conventional PAPR0 values for FLIP and ACO -OFDM were 16.44 dB and 15.58 dB, respectively. However, after adding the precoding technique, the proposed PAPR0 values were 13.17 dB and 13.32 dB, respectively. This resulted in PAPR0 reduction values of 3.27 dB for ACO-OFDM and 3.26 dB for FLIP-OFDM. Notably, the PAPR0 reduction values for FLIP and ACO-OFDM