# Wheel-Based MDM-PON System Incorporating OCDMA for Secure Network Resiliency
## 3 Results and Discussion  
In this segment, the results obtained from the design of the hybrid MDM-based TWDM-PON system utilizing MWZCC code are depicted and discussed for both downlink and uplink transmission considering the \(10^{-3}\) BER threshold in OptiSystem software. Figure 6 presents the BER performance of the 10/2.5 Gbit/s hybrid MDM-OCDMA-PON system over 1 km fiber distance for both users operating modes 0 and 1 in downstream and upstream transmission. The BER threshold of \(10^{-3}\) by a dashed line is also displayed. It was noted that the system operating at mode 0 for User 1 in uplink transmission offers the best performance out of all modes. Furthermore, User 2 operating at mode 1 in uplink performs better than both downlink users, i.e., User 1 at mode 0 followed by User 2 at mode 1. The proposed system offers the minimum required received power of \(-31\) and \(-28\) dBm for User 1 and User 2, respectively, in the upstream transmission. Moreover, the minimum received power for User 1 and User 2 is \(-27\) and \(-25\) dBm, respectively, in the downstream direction. The measured eye patterns at \(-20\) dBm received optical power for \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Parameters**} & \multicolumn{2}{c}{**Values**} \\ \hline Laser input power (downlink) & 10 dBm \\ Laser input power (uplink) & 0 dBm \\ Wavelength (downlink) & 1596–1602.8 nm \\ Wavelength (uplink) & 1527–1533.8 nm \\ Data rate (downlink) & 10 Gbit/s \\ Data rate (uplink) & 2.5 Gbit/s \\ Reference wavelength & 1550 nm \\ Dark current & 9 nA \\ Measured index multimode fiber length & 100–800 m \\ Dispersion & 17 ps/nm \(\times\) km \\ Attenuation & 0.25 dB/km \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters used [34]. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Parameters**} & \multicolumn{2}{c}{**Values**} \\ \hline Laser input power (downlink) & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm & 10 dBm \\ Laser input power (uplink) & 10 dBm  
both User 1 at mode 0 in both downlink and uplink directions, illustrating the successful transmission of traffic. Figure 7 depicts the BER performance of the 10/2.5 Gbit/s hybrid MDM-OCDMA-PON system employing MWZCC code over 1 km fiber distance for downstream and upstream transmission, respectively, at mode 0 and mode 1 for both Users 1 and 2. It is noted that as the MMF length of fiber exceeds, the BER value increases; therefore, the system's performance diminishes for all end users in both modes 0 and 1. Moreover, the uplink transmission performs better than the downlink as the former operates at a lesser data rate and low input power than the latter, which causes fewer impacts of fiber impairments on uplink transmission. This system performance degradation is because of the presence of non-linearities and noise in the fiber link. Moreover, User 1 operating at mode 0 performs better than User 2 operating mode 1 in both upstream and downstream transmission. It further presents that User 1 and User 2 achieve acceptable \(\leq\)10\({}^{-3}\) BER at the MMF length of 1.6 and 1.3 km, respectively, in the upstream direction. Likewise, for User 1 and User 2, under the BER threshold, the obtained fiber length is 1.2 and 1 km, respectively, in the downstream direction. The computed eye patterns at the 1 km fiber range illustrate the faithful transmission of end users. MDM operates with multiple optical modes, and these modes are limited to being connected with other propagating modes because they pass through MMF. Here, mode 0 performed better than mode 1 in both downlink and uplink transmission. It is due to the reason that the traveling higher-order modes in MMF are more absorbed or scattered (due to fiber attenuation) than lower-order modes.