# Modeling of Satellite-to-Underwater Integrated FSO-PON System Using NOMA-VLC
## 4 Results and Discussion
Figure 7: OSNR versus received optical power of the hybrid FSO-PON system VLC under Clear Ocean, coastal ocean and turbid harbor for DN and UP transmission. Figure 8: _Cont_. Figure 8: Output OTD as well as eye diagrams of (**a**) downlink as well as and (**b**) uplink received data signals over back-to-back, 10, 50 and 100 km fiber length. Moreover, the respective eye patterns over 0, 10, 50 and 100 km fiber length are also depicted in Figure 8a for downlink and in Figure 8b for uplink to support the above discussions. As the eye-opening diminishes, i.e., eye distortion increases, BER improves and QF decrease with the improvement in fiber length. The better performance can be seen for uplink channels. Figure 9a,b presents the performance of the proposed system over variable fiber distance in terms of RF spectra and its respective 3D BER patterns for DN and UP received signals, respectively. The fiber distance increases from back-to-back to 100 km and the RF spectra become distorted and comprise low output power. Again, UP transmission (minimum ROP =  
Figure 9: _Cont_. From Tables 10 and 11, it is shown that the suggested system utilizing the MNZCC code has better performance than other codes and system designs, respectively. In the recommended system, the MNZCC code has less code weight and length, a maximum number of connected devices and zero cross-correlation properties. Additionally, regarding the rate and distance of transmission, the recommended design provides a maximum fiber transmission distance of 100 km, with 10 km FSO and 15 m VLC range at a traffic rate of 10/2.5 Gbps to support more than 250 simultaneous devices in both UP and DN directions. Moreover, the practical realization of the proposed work adds complexity to the CO side, as it would also be \"natural\" as well as less expensive to simply establish the TWDM-WDM channels on FSO-VLC using OCDMA codes. Furthermore, separate input light \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Ref.** & **Code** & **Connected** & **Code Weight** & **Length of** & **Cross-** \\  & **Device** & **Code** & **Code** & **Correlation** \\ \hline
[52] & Dynamic cyclic shift (DCS) & 30 & 4 & 30 & \textless{}1 \\
[11] & Modified quadratic congruence (MQC) & 68 & 4 & 12 & 1 \\
[53] & Modified double weight (MDW) & 9 & 16 & 30 & 1 \\
[23] & Flexible cross-correlation (FCC) & 30 & 4 & 10 & 1 \\
[27] & Hadamard & 30 & 16 & 32 & \textless{}1 \\
[54] & Zero cross-correlation (ZCC) & 48 & 4 & 20 & 0 \\
[55] & Enhanced double weight (EDW) & 10 & 4 & 30 & \textless{}1 \\ Proposed system & MNZCC & 290 & 1 & 3 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Comparisons of proposed work using MNZCC code with other codes. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Ref.** & \begin{tabular}{l} **Highest Data** \\ **Rate (Gbps)** \\ \end{tabular} & \begin{tabular}{l} **Maximum** \\ **Fiber Length (km)** \\ \end{tabular} & \begin{tabular}{l} **Maximum FSO** \\ **Range (km)** \\ \end{tabular} & \
\begin{tabular}{l} **Maximum VLC** \\ **Range (m)** \\ \end{tabular} &
\begin{tabular}{l} **System Complexity** \\ **Level** \\ \end{tabular} \\ \hline
[56] & 10/2.5 & 20 & not defined & not defined & Moderate \\
[57] & 10/1.25 & not defined & 0.05 & not defined & Moderate \\
[58] & 10/2.5 & 50 & not defined & 10 & High \\
[16] & 0.0126 & not defined & 0.05 & 1 & High \\
[59] & 10 & 20 & not defined & 4.5 & High \\ Proposed system & 10/2.5 & 100 & 10 & 15 & Moderate to high \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Comparisons of proposed work with other systems design in the recent literature. Figure 9: RF spectra and 3D BER pattern of (**a**) downlink and (**b**) uplink received signals at back-to-back, 10, 50 and 100 km fiber length. sources and modulators were required to generate a single wavelength signal in the PON-FSO-VLC system. This increases the system configuration cost and complexity.