# Wheel-Based MDM-PON System Incorporating OCDMA for Secure Network Resiliency
## 4 Conclusions  
In this work, a 10/2.5 Gbit/s hybrid MDM-PON system incorporating OCDMA was designed. Donut modes 0 and 1 are utilized in the MDM scheme in both downlink and uplink transmission. The system operating at mode 0 performs better than mode 1 for MWZCC code as compared to ZCC, RD and MD code. For acceptable BER, the minimum required received power is \(-\)31 dBm in upstream and \(-\)27 dBm downstream over 1 km length at a 10/2.5 Gbit/s data rate. The faithful transmission distance of 1.6 km in uplink and 1.2 km in a downlink can be achieved at 10/2.5 Gbit/s successfully. Moreover, the MWZCC code offers minimum acceptable received power of \(-\)20 dBm in uplink and \(-\)30 dBm downlink direction for User 1 operating at mode 0. Moreover, the maximum number of ONUs handled by the system using the MWZCC code is 58 in both uplink and downlink transmission. The numerical measured influence of fiber impairments and \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multirow{2}{*}{**Scheme**} & **Maximum Transmission Transmission Distance (km)** & **Highest Data Rate (Gbit/s)** & **No. of ONUs** & **Code Used** & **Design Features** \\ \hline Hybrid tree-ring topology-based radio over fiber system [42] & 26 & 1.25 & 4 & Not used & Complex and costly \\ Ring-based WDM system [43] & 60 & 2.5 & 10 & Not used & Not scalable, losses and not secure \\ Ring-based WDM system [44] & 15 & 10 & 6 & Not used & Not scalable, losses and not secure \\ WDM Ring network [45] & 10 & 2.5 & 4 & Not used & Not scalable, losses and not secure \\ Ring-based hybrid PON-FSO [34] & 10 (fiber) and 40 (FSO) & 1000 & 50 & Single weight ZCC & Not scalable, costly and more losses \\ Proposed scheme & 1.6 & 10/2.5 & 58 & MNZCC & Scalable and fewer losses \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparisons of proposed scheme with other reported schemes. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multirow{2}{*}{**Length (km)**} & **Fiber Loss \(aL_{fiber}\) (dB)** & **2:1 Power Combiner (dB)** & **1:2 Power Splitter (dB)** & **Total Loss (dB)** \\ \hline
0.2 & 3.4 & 0.3 & 3.6 & 7.3 \\
0.6 & 10.2 & 0.3 & 3.6 & 14.1 \\
1 & 17 & 0.3 & 3.6 & 20.9 \\
1.2 & 20.4 & 0.3 & 3.6 & 24.3 \\
1.6 & 27.2 & 0.3 & 3.6 & 31.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Analysis of loss budget in the proposed scheme. splitters/combiners depicts that a wheel-based scheme is a preferable approach for future networks. Moreover, it shows better outcomes than other existing schemes. In addition, as the proposed scheme has various pros, it also poses some cons. The major benefit of the proposed wheel-based scheme is to offer reliable topology for fast access communication. It also improves the network protection from fiber break or failure and lowers the link connection failure impact from OLT to ONUs and vice-versa. Additionally, the proposed work lacks to consume surplus fiber capacity, as the channel capacity will be utilized under the link break/failure scenario. Additionally, the presence of embedded devices such as switches with OLT to control the traffic to the respective ONU is required, as in ring topology-based systems. In the future, a network resilience wheel-based OCDMA-based MDM-PON system can enhance the usage of the link under the presence of fiber break/failure, interference or dispersion. Conceptualization, M.K. and H.M.R.A.-K.; methodology, M.K., V.A. and H.M.R.A.-K.; software, M.K., V.A. and H.M.R.A.-K.; validation, M.K., V.A. and H.M.R.A.-K.; formal analysis, V.A. ; investigation, V.A. and H.M.R.A.-K.; resources, M.K. and H.M.R.A.-K.; writing--original draft preparation, M.K., V.A. and H.M.R.A.-K.; writing--review and editing, M.K., V.A. and H.M.R.A.-K.; visualization, M.K., V.A. and H.M.R.A.-K.; project administration, H.M.R.A.-K. All authors have read and agreed to the published version of the manuscript. There is no funding. All data are available in this paper. The authors declare no conflict of interest.