## 4 Results and Discussion
To balance this, our design uses appropriately sized transmitter optics and a large receiving aperture. A larger receiver lens not only captures more of the diverging beam power but also provides aperture averaging, which smooths out intensity fluctuations [47]. This effectively mitigates scintillation and reduces BER under turbulence. In summary, harsh environmental conditions (fog, rain, temperature-induced turbulence) will increase required link margins and can degrade BER, but careful system design--such as high transmit power, robust FEC (LDPC), and large-aperture receivers--can compensate for these effects. By designing for worst-case conditions, including some margin for pointing error and beam spreading, the WDM-PON-FSO system can maintain reliable fronthaul connectivity even in challenging weather. The Peak-to-Average Power Ratio (PAPR) is a key factor in OFDM-based optical networks, influencing nonlinear distortions and efficiency, especially in WDM-PON-FSO systems. Its relationship with OSNR offers insights into system resilience against noise and optical impairments. As depicted in Figure 4, the PAPR vs. OSNR trends show that increasing the OSNR leads to a reduction in PAPR across every examined channel. At lower OSNR values, such as 12 dB, heightened noise levels induce waveform distortions that amplify power fluctuations, resulting in higher PAPR. For example, at 193.1 THz, PAPR reaches roughly 10.2 dB when the OSNR is 12 dB, while at 194.3 THz, it stands at 9.8 dB. As the OSNR rises to 32 dB, these values decrease to 8.5 dB and 7.9 dB, respectively, signifying improved signal uniformity and fewer power peaks. LDPC coding contributes to an even lower PAPR by counteracting noise-induced waveform distortions and evening out the power distribution. Post-decoding, the PAPR shows an average reduction of 1.5-2 dB at all frequencies: at 193.85 THz, for instance, PAPR drops from 9.5 dB at 12 dB OSNR to 7.3 dB once LDPC is applied, and at 194.65 THz, PAPR descends from 10.1 dB to 7.1 dB under high OSNR. This improvement arises from LDPC's capacity to rectify errors and diminish high-power spikes within the signal. Interestingly, PAPR remains largely similar across each measured frequency. This uniformity stems from the inherent statistical qualities of OFDM signals, which do not significantly depend on carrier frequency. Because each WDM channel utilizes the same OFDM configuration and power adjustments,their PAPR distributions are consistent across the band. Additionally, in a linear optical chain, identical dispersion and attenuation conditions apply to all WDM signals, thereby preserving uniform PAPR behavior. These results emphasize the critical role of PAPR reduction in high-capacity optical networks and the necessity of advanced LDPC coding in WDM-PON-FSO systems. It is worth noting that the use of OFDM in our FSO system provides certain advantages despite the primarily line-of-sight channel. OFDM enables high spectral efficiency by overlapping subcarriers and allows easy integration of multiple access techniques. Even though the FSO channel does not experience multipath frequency-selective fading in the way RF channels do, the OFDM modulation helps mitigate any potential intersymbol interference (ISI) from transmitter and receiver filtering or slight atmospheric dispersion. It also simplifies equalization, as each subcarrier can be treated as flat-fading. Moreover, using an OFDM format aligns with the 5G New Radio waveform, meaning the fronthaul can directly carry OFDM-modulated radio signals without waveform translation. This compatibility is valuable in C-RAN architectures. Therefore, the rationale for employing OFDM extends beyond diversity against multipath; it ensures maximal spectral efficiency and high data rate transmission in our WDM-PON-FSO link while maintaining robustness against any form of distortion or ISI present in the optical channel.