# Fuzzy Logic-Based Performance Enhancement of FSO Systems Under Adverse Weather Conditions
## 3 Fuzzy Modeling for Enhancing Receiver Performance in FSO System
### Adaptive BER Threshold Adjustment Mechanism for FSO-FLC-OCDMA Receivers
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Weather** & **No. of Users** & **BER with FLC** & **BER Without FLC** & **Improvement (\%)** \\ \hline Low Rain & 22 & \(6.44\times 10^{-9}\) & \(4.20\times 10^{-7}\) & 98.47\% \\ Medium Rain & 20 & \(3.35\times 10^{-9}\) & \(2.56\times 10^{-7}\) & 98.69\% \\ Heavy Rain & 10 & \(9.97\times 10^{-9}\) & \(1.03\times 10^{-7}\) & 90.32\% \\ Low Fog & 21 & \(7.82\times 10^{-9}\) & \(4.87\times 10^{-7}\) & 98.39\% \\ Medium Fog & 19 & \(2.25\times 10^{-9}\) & \(1.90\times 10^{-7}\) & 98.82\% \\ Heavy Fog & 9 & \(5.17\times 10^{-9}\) & \(6.24\times 10^{-7}\) & 99.17\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Average BER performance comparison with and without FLC. thresholds and optimize transmission parameters, thereby mitigating the negative impact of atmospheric attenuation. Figure 21 shows the BER versus the number of simultaneous users for an FSO system using an SSM code at 2.5 Gbps under heavy fog (HF) conditions when w = 8. This compares system performance with and without FLC across various FSO ranges. At a BER of \(10^{-3}\), the system without FLC supports 28 and 100+ users at FSO spans of 1.1 km and 0.5 km, respectively. However, the corresponding values for the FLC-enabled system are 35 and 105 users with similar parameters. At a more stringent BER of \(10^{-9}\) and FSO propagation range of 0.5 km, the system supports 70 and 85 users without and with FLC, respectively. At 1.1 km, these values decrease to 21 and 19 users, respectively, which further confirms the

Figure 19: Three-dimensional surface of fuzzy model output of the two inputs: distance L (km) and rainfall (mm/h/km). Figure 20: Number of active users vs. BER under LF weather condition. detrimental effect of increased transmission distance on system capacity. The performance improvement observed with FLC is attributed to its ability to dynamically adjust system thresholds and optimize transmission parameters, thereby mitigating the negative impact of atmospheric attenuation. Similarly, under foggy weather conditions, Table 5 confirms that the dynamic adjustment provided by the FLC maintains significantly lower BER levels compared to the system without FLC. Despite the severity of fog-induced attenuation, the FLC consistently improves system resilience across varying user loads, achieving BER improvements ranging from 98.39% to 99.17%. These results highlight the robustness of the proposed FLC in maintaining performance under highly absorptive and scattering atmospheric conditions. ## 5 Conclusions

In this paper, we proposed a fuzzy control system for SSM SAC-OCDMA receivers to dynamically tune the detection threshold level at the receiver unit due to variations in the weather conditions in an FSO network. The FLC system dynamically adjusts the receiver threshold values based on the received power values. The system with FLC can increase the network propagation distance. Alternatively, it supports a larger number of users with different weather conditions compared to an FSO system without FLC. An acceptable BER in FSO ranges from \(3.8\times 10^{-3}\) to \(10^{-6}\) for many applications, whereas for demanding applications such as high-definition video streaming, BER values in the range of \(10^{-9}\) or lower may be required. Under low rain weather conditions, almost 7 and 12 users for a system without and with FLC for 2.8 km at BER of \(10^{-9}\) were supported. Under low fog weather conditions, 18 and 22 users were supported for a system without and with FLC for 0.5 km when the BER is set to \(10^{-9}\). The proposed FSO system with FLC is shown to adjust BER threshold values automatically and dynamically to maintain a reliable performance by tuning transmission parameters that affect the received power. Numerical values show that the system with FLC outperforms a system without FLC receiver module by almost twice the number of simultaneous users.