# Optical-OFDM VLC System: Peak-to-Average Power Ratio Enhancement and Performance Evaluation
## 4 PAPR Reduction Methodology and Proposed Model
### Proposed PAPR Reduction System
CCDF = \(10^{-3}\), the value of PAPR0 for various modulation orders at a 13 dB DC bias level yielded superior evaluation results compared to the 10 dB and 7 dB DC bias levels. At a 13 dB DC bias level, the DCO-OFDM with a 4-QAM modulation yielded a lower PAPR0 value of 5.91 dB and increased to 6.14 dB with a 1024 modulation order. The DCO-OFDM with a 16-QAM modulation produced a lower PAPR0 value of 7.71 dB at a 10 dB DC bias level, but under the same bias condition, it increased to 7.962 with a 4-QAM modulation order. At a 7 dB DC bias level, the DCO-OFDM with a 1024-QAM modulation yielded a lower PAPR0 value of 9.36; however, a 4-QAM modulation order provided 9.625 dB. The average PAPR0 value across different modulation orders was 6.034 dB at a 13 dB DC bias, 7.834 dB at 10 dB, and 9.51 dB at 7 dB. According to this, the DC bias greatly affected the value of PAPR0 in DCO-OFDM. Still, for the DCO-OFDM, changing the modulation order did not result in a meaningful change in PAPR0. ### Exploring BER and PAPR for ACO-OFDM

Figure 12a explores the BER assessment for ACO-OFDM. This scheme does not require a DC bias level like DCO-OFDM. However, for BER = \(10^{-4}\) with a 4-QAM modulation order, the E\({}_{\text{b}}\)/N\({}_{\text{O}}\) for unipolar ACO decreased by 3.16 dB compared to bipolar ACO, mainly due to the clipping effect for transmitting the data via LEDs. For that reason, the primary focus of this research was on the thorough analysis and assessment of O-OFDM systems. This means analyzing the final broadcast and received signals and the system overall and accounting for the effects of clipping noise. As the modulation order of ACO-OFDM increased as the transmitted data rate increased, E\({}_{\text{b}}\)/N\({}_{\text{O}}\) performance deteriorated. At a BER = \(10^{-4}\), the E\({}_{\text{b}}\)/N\({}_{\text{O}}\) decreased by an average value of approximately 4.4325 dB when transitioning from one modulation order to another. The CCDF of ACO-OFDM is depicted in Figure 12b. Table 6 illustrates the PAPR0 values of ACO-OFDM for various modulation orders at a CCDF of \(10^{-3}\). The minimum PAPR0 value was attained at a CCDF of \(10^{-3}\) with a 1024-QAM modulation order, while the maximum PAPR0 value was observed with a 4-QAM modulation order. The average PAPR0 value, computed from multiple evaluation data points, was 16.48 dB, while the PAPR0 median value was 16.44 dB at the 16-QAM modulation order. ### Exploring BER and PAPR for FLIP-OFDM

The BER evaluation for FLIP-OFDM is displayed in Figure 13a. When the transmission data rate of FLIP-OFDM rose, the E\({}_{\text{b}}\)/N\({}_{\text{O}}\) performance decreased. On average, there was a reduction of 4.4225 dB in E\({}_{\text{b}}\)/N\({}_{\text{O}}\) when transitioning between modulation orders at a BER

Figure 12: Performance of ACO-OFDM for (**a**) BER and (**b**) PAPR. of \(10^{-4}\). The numerical results presented in Table 6 indicate that, at different constellation sizes, the \(\rm E_{b}/N_{O}\) values for FLIP and ACO-OFDM were nearly the same. Figure 13b illustrates the CCDF performance of FLIP-OFDM. The resemblance in \(\rm E_{b}/N_{O}\) values between FLIP-OFDM and ACO-OFDM for various modulation orders suggests that their PAPR0 values are nearly identical. Additionally, it is worth noting that the PAPR0 of FLIP-OFDM did not exhibit significant changes as the modulation order was varied. The numerical values of PAPR0 at a CCDF of \(10^{-3}\) for various modulation orders are provided in Table 6. For FLIP-OFDM evaluation results at a CCDF of \(10^{-3}\), 16.69 dB was the median PAPR0 value for the 1024-QAM modulation order. ### Exploring BER and PAPR for ADO-OFDM

In Figure 14a, the ADO-OFDM system's BER is assessed and displayed. ADO-OFDM, similar to DCO-OFDM, requires a DC bias value before clipping the time sampled signal before transmitting through LEDs. Hence, the performance of ADO-OFDM varies with alterations in the DC bias value. We assessed the BER performance at 7 dB, 10 dB, and 13 dB DC bias values.