# Optical-OFDM VLC System: Peak-to-Average Power Ratio Enhancement and Performance Evaluation
## 4 PAPR Reduction Methodology and Proposed Model
### Proposed PAPR Reduction System
### Investigating the Relationship between Spectral Efficiency and BER for Various O-OFDM Methodologies

After thoroughly evaluating the various factors affecting the choice of MCM techniques previously discussed, these elements are amalgamated in Figure 11:0 This visual depiction showcases the relationship between the spectral efficiency of different MCM techniques, their respective \(\mathrm{E_{b}}/\mathrm{N_{O}}\) across diverse constellation sizes, and the average PAPR demonstrated by these techniques. The numerical outcomes derived from both Table 6 have been translated into a visual format and are presented in Figure 11:1

Both the ACO-OFDM and FLIP-OFDM approaches yielded similar \(\mathrm{E_{b}}/\mathrm{N_{O}}\) values across various spectral efficiencies at different modulation orders and demonstrated equivalent average PAPR values. Furthermore, due to the rapid increase in \(\mathrm{E_{b}}/\mathrm{N_{O}}\) as spectral efficiencies increased, it indicates that these two approaches are characterized as spectrally inefficient methods. The \(\mathrm{ASCO}\)-OFDM and \(\mathrm{LACO_{2}}\)-OFDM approaches delivered identical spectral efficiency and average PAPR values, although \(\mathrm{LACO_{2}}\)-OFDM offered lower \(\mathrm{E_{b}}/\mathrm{N_{O}}\) values across different modulation orders. The ADO-OFDM and DCO-OFDM methods yielded increased spectral efficiency values compared to other approaches, yet they also entailed higher \(\mathrm{E_{b}}/\mathrm{N_{O}}\) values at equivalent modulation orders. Moreover, both methods presented varying average PAPR values associated with the chosen DC bias level. The DCO-OFDM approach exhibited superior BER and PAPR performance compared to the ADO-OFDM approach for various modulation orders at different DC bias levels. The spectral efficiency, \(\mathrm{E_{b}}/\mathrm{N_{O}}\) values, and PAPR values offered by \(\mathrm{LACO}\)-OFDM varied according to the number of layers employed in the technique. With an increase in the number of layers, there was a corresponding rise in spectral efficiency and \(\mathrm{E_{b}}/\mathrm{N_{O}}\) values. However,

Figure 11:2 The \(\mathrm{E_{b}}/\mathrm{N_{O}}\) needed for distinct levels of spectral efficiency at a BER of \(10^{-4}\) for the DCO-OFDM, ACO-OFDM, FLIP-OFDM, ADO-OFDM, \(\mathrm{ASCO}\)-OFDM, and \(\mathrm{LACO}\)-OFDM techniques, considering alterations in constellation size. this escalation was accompanied by a higher computational complexity. Interestingly, despite these increments, the average PAPR value decreased. Investigating the Influence of VLM Precoding Methodology on BER and PAPR for Different O-OFDM Approaches

After conducting an extensive analysis of the BER and PAPR performance for MCM techniques used in VLC systems, a pressing need arose to explore a novel approach. This evaluation is essential to address the inherent constraints in these systems, with a particular emphasis on alleviating nonlinearity effects. The purpose of this section is to underscore the importance of the new technique by investigating its impact on BER and PAPR performance in comparison to the existing MCM approaches. Additionally, this work introduces two parameters, PAPR\({}_{\text{reduction}}\) and E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\), for comparative analysis. PAPR\({}_{\text{reduction}}\) is characterized as the decrease in PAPR0 of the new approach relative to the conventional PAPR0. This is computed mathematically by subtracting the PAPR0 of the proposed methodology from the conventional PAPR0 for different MCM approaches at a CCDF of \(10^{-3}\). A higher PAPR\({}_{\text{reduction}}\) value signifies that a more effective PAPR reduction technique has been utilized. Figure 11:3

The parameter E\({}_{\text{b}}\)/N\({}_{\text{0 difference}}\), on the other hand, is defined as the disparity between the conventional and the newly E\({}_{\text{b}}\)/N\({}_{\text{0}}\) after applying the PAPR degradation methodology.