## 4 Computer Simulation
### Evaluation of Rician Fading Impact on and Effectiveness of Proposed Method Using FSS  
In the previous section, evaluations were conducted in an AWGN environment. To address conditions closer to real-world scenarios, specifically Rician fading environments, the proposed method integrated with FSS was evaluated. Since the previous section demonstrated that the nonlinear coefficient estimation using LSM achieved favorable estimation accuracy, the focus of this evaluation was on LSM. The simulation parameters were modified from those listed in Table 1, specifically altering the channel model and the number of reference signals. The channel model was configured to represent a three-path Rician fading environment, and the number of reference signals was set to 300. To evaluate the BER performance under Rician fading, we introduce a parameter known as the K-factor. The K-factor in Rician fading is defined as follows:  
\[K=\frac{P_{LOS}}{P_{NLOS}}. \tag{16}\]  
where \(P_{LOS}\) is the power of the Line-of-Sight (LOS) component, while \(P_{NLOS}\) is the total power of the Non-Line-of-Sight (NLOS) components. The K-factor typically ranges from 5 to 25 dB in office environments [20]. In this section, to verify the effectiveness of the method under more challenging conditions, K-factors of 0, 5, and 10 dB were set. Additionally, the lighting conditions remained consistent with those in the previous section. The BER performance of the proposed method with and without FSS is illustrated in Figures 10-12. The proposed method utilizing FSS demonstrated an improvement in \(E_{b}/N_{o}\) by approximately 4.0 dB at \(K\) = 0 dB and 1.5 dB at \(K\) = 5 dB for a BER of \(10^{-4}\). However, almost no improvement was observed at \(K\) = 10 dB. This is attributed to the increasing dominance of the LOS component as \(K\) increases, which diminishes the effectiveness of SNR equalization by FSS. Interestingly, for all K-factors, the uncompensated LED exhibited slightly worse BER performance when FSS was used. This degradation is likely due to the nonlinear distortion of the LED, which disrupts the orthogonality of the multiplied \(C_{PN}\) during transmission, leading to signal deterioration during despreading at the receiver. Supporting this observation, the BER performance of the linear LED and the proposed compensation method showed better results when FSS was employed. This improvement is attributed to the preservation of \(C_{PN}\) orthogonality through distortion compensation. \begin{table}
\begin{tabular}{c c} \hline \hline
**Modulation** & **16 QAM, 64 QAM** \\ \hline Transmission bandwidth & 20 MHz \\ \hline FFT size & 128 \\ \hline Number of subcarriers & 128 \\ \hline Number of data symbols & 32 \\ \hline Guard interval & 16 \\ \hline Channel model & AWGN \\ \hline Number of pilot symbols & 2 \\ \hline LED type & White LED (\(\xi\) = 0.582) \\ \hline \multirow{3}{*}{Number of reference signals (\(N\))} & LSM (16 QAM): 50 \\  & MBM (16 QAM): 600 \\  & LSM \(\cdot\) MBM (64 QAM): 750 \\ \hline Normalized bias current (\(I_{DC}\)) & 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. The estimation accuracy of nonlinear coefficients using the proposed method, with and without FSS, in a Rician fading environment is shown in Figure 13. As in the previous section, each simulation was conducted with a fixed \(E_{b}/N_{o}\) = 21 dB. Figure 11: BER Performance of proposed method in Rician fading environment (\(K\) = 5 dB). Figure 10: BER performance of proposed method in Rician fading environment (\(K\) = 0 dB). When the proposed method employs FSS, as well as when it does not, the estimation performance remains almost unchanged regardless of the increase or decrease in the K-factor. This can be attributed to the fact that the BER performance of the uncompensated nonlinear LED is unaffected by variations in the K-factor, implying that the quality of the regenerated signal before distortion \(\dot{x}_{n}\), which is used for nonlinear coefficient estimation, is not significantly influenced by the K-factor.