## 6 Conclusions  
In this work, we studied and enhanced the HFFSO optical fiber communication network system using the hybrid modulation techniques of OOK/M-ary DPPM-M-PAPM, based on the DWDM-PON network. ICC analyses for DWDM-DPPM systems are given for the GA, CB, and MCB. Also, we consider using hybrid OOK/M-ary DPPM-M-PAPM modulation techniques to increase spectral efficiency and incorporate adaptive optics to mitigate the crosstalk interferences in the DWDM-PON/HFFSO scenarios for improved reliability. The BER performances are then theoretically analyzed. In the presence of atmospheric modulation, the proposed proposed approach is not applicable to the proposed approach. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Ref. [50]** & **[Proposed Work]** \\ \hline \multirow{2}{*}{**Modulation scheme technique**} & hybrid MAPPM technique & hybrid MAPPM technique & hybrid MAP-PAPM-DPPM-based DWDM FSO \\  & deep space optical link & & optical fiber network \\ \hline \multirow{2}{*}{**OSNR improved**} & \multirow{2}{*}{1 dB and 2 dB} & \multirow{2}{*}{4-8 dB} \\ \cline{1-1} \cline{3-3}  & & & \\ \hline
**Target BER** & \(10^{-6}\) & & \(10^{-12}\) \\ \hline \multicolumn{2}{c}{**Optical pulses per frame for \(M\)**} & \multirow{2}{*}{16} & \multirow{2}{*}{16} \\ \end{tabular}
\end{table} 
Table 4: Performance comparison of proposed M-ary DPPM-M-PAPM based-DWDM-FSO optical fiber link with reference [50]. Figure 10: BER vs. AOP at RCL input (dBm) for DPPM and OOK for no turbulence and WT with all apertures averaging (AA). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Ref. [2]** & **Ref. [5]** & **Ref. [8]** & **Ref. [9]** & **Ref. [15]** & **Ref. [42]** & **[Proposed Work]** \\ \hline \multirow{3}{*}{**Technique used**} & \multirow{3}{*}{DPPM-FSO} & WDM-FSO & \multirow{3}{*}{DPPM-based} & M-ary & WDM-FSO & DPPM-based & hybrid M-ary-PAPM \\  & & hybrid & DWDM-FSO & & PPM-based & network-based & WDM-FSO & M-DPPM-based DWDM FSO \\  & & link & fiber-based & \multirow{3}{*}{system} & WDM - PSO & DPPM & communication & \multirow{3}{*}{} & \multirow{3}{*}{} \\  & DPPM & system & system & modulation & system & optical fiber network & \\ \multicolumn{2}{c}{**Data rate**} & 2.5 Gbps & 2.5 Gbps & 2.5 Gbps & 2.5 Gbps & 2.5 Gbps & 2.5 Gbps & 2.5 Gbps \\ \multicolumn{2}{c}{**Net capacity**} & 2.5 Gbit/s & 5 Gbit/s & 20 Gbit/s & 20 Gbit/s & 5 Gbit/s & 5 Gbit/s & 20 Gbit/s \\ \multicolumn{2}{c}{**Maximum link**} & 1500 m & 2000 m & 4000 m & 2500 m & 2000 m & 2000 m & 4000 m \\ \multicolumn{2}{c}{**Quantum efficiency**} & 0.75 & 0.8 & 1 & 1 & 0.8 & 0.9 & 1 \\ \multicolumn{2}{c}{**No. of channels**} & 1 & 2 & 8 & 8 & 2 & 2 & 8 \\ \multicolumn{2}{c}{**Target BER**} & \(10^{-12}\) & \(10^{-12}\) & \(10^{-12}\) & \(10^{-12}\) & \(10^{-12}\) & \(10^{-12}\) & \(10^{-12}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Performance comparison of the proposed M-ary DPPM-M-PAPM based-DWDM-FSO optical fiber link with contemporary literature. spheric turbulences, the OOK/M-ary hybrid DPPM modulation scheme is an excellent way to increase DWDM-PON/HFFSO efficiency. Furthermore, the results obtained show that the ICC interferences could be effectively suppressed thanks to the M-ary DPPM-M-PAPM modulation and that the proposed system could achieve superior BER performance. We investigate the impact of the turbulence effect on the proposed system performance based on OOK-M-ary-DPPM modulation as a function of M and other atmospheric parameters. The proposed design of the M-ary DPPM-M-PAPM can improve the power penalty over OOK-NRZ and enhances performance efficiency. The proposed M-ary DPPM-M-PAPM architecture can enhance the receiver sensitivity and reliability over OOK-NRZ.