## 5 Comparison with Related Studies  
This section provides a detailed specification comparison between this work and related literature. It is worth mentioning that the key differences between this work's technique (cross-seeding) and other techniques related to the critical requirements for the DWDM-PON system are already discussed in Section 1. In addition, the reasons, which have motivated us to use the cross-seeding technique, are also discussed there. Table 2 represents a detailed specification and value comparison between this work and related studies. Again, as mentioned in Section 1, the comparison includes literature not only for DWDM-PON systems and WDM-PON, but also for Hybrid WDM/TDM-PON and other related systems. For example, in [5], the number of channels, US, and DS rates are remarkable, but the problems associated with the use of (FP-L) (mentioned in Section 1) limit the transmission distance, the ability to use more channels (i.e., channel spacing), and the BER. Besides the FP-L influence, this work utilizes a higher Dispersion Compensation Fiber (DCF) length of \(-340\) ps/nm to provide the aforementioned \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref** & **System** & **No. of Channels** & **Maximum 1** & **Minimum 2** & **Maximum 1** & **Maximum** & **Optimum** \\  & & & **Length Km** & **Channel** & **US Bit Rate** & 1 & **DS Bit** & **BER** \\ \hline
[5] & WDM-PON & 16 & 15 & 140 & 10 & 10 & \(10^{-9}\) \\
[6] & DWDM-PON & 3 & 25 & 200 & 2.5 & 2.5 & \(10^{-9}\) \\
[7] & DWDM-PON 3 & 2 & 25 & 100 & 1.25 & 10 & \(10^{-9}\) \\
[8] & Class C GPON 4 & 1 & NA & & 10 & 10 & \(10^{-10}\) \\
[9] & WDM-PON & 4 & 20 & NA & 10 & 10 & \(10^{-4}\) \\
[10] & WDM-PON & 1 & 20 & & 40 & 40 & \(10^{-4}\) \\
[11] & WDM-TDM & 2 & 20 & & 50 & 2.5 & 10 & \(10^{-9}\) \\ Migration scheme & & & & & & & \(<\)10\({}^{-9}\) for DS \\
[18] & from TDM-PON & 1 & 20 & & & 10 & \(10^{-3}\) for US \\ to WDM-PON & & & & & & & \\  & Long-Reach & & & & & & \\ Bidirectional & 1 & 115 & & & 2.5 & 10 & \(10^{-10}\) \\
[19] & Centralized & & & & & & \\ WDM-PON & & & & & & & \\ WDM-PON With & & & & & & & \\
[20] & Wavelength & 1 & 25 & & 1.25 & 2.50 & \(10^{-9}\) \\  & Shifting in & & & & & & \\  & Colorless ONU & & & & & & \\
[21] & Hybrid & & & & & & \\ WDM/TDM-PON & 8 & 45 & 100 & 2.5 & 2.5 & \(10^{-7}\) \\
[22] & DWDM-PON & 6 & 25 & 25 & 1.25 & 10 & \(10^{-9}\) \\
[23] & WDM-PON & 2 & 25 & 100 & 1.25 & 10 & \(10^{-10}\) \\
[34] & WDM-PON & NA & 25 & NA & NA & NA & \(10^{-9}\) \\ This work & DWDM-PON & 16 & 25 & 12.5 & 2.5 & 10 & \(10^{-12}\) \\ \hline \hline \end{tabular}  
* The maximum value achieved through several experiments and simulation trials. 2 The minimum value achieved through several experiments and simulation trials. 3 DRWDM-PON are WDM-PONs that employ directly modulated lasers (DMLs) at the CO and RSOAs at the ONUs. 4 GPON = Gigabit passive optical network.  
\end{table} 
Table 2: A comparison between the studies and the presented work for different optical network systems. performance characteristics in Table 2 for 15 km. The effect of, and price of, the high length DCF can be found in many dispersion compensation-related studies, such as [35; 36]. Finally, an in-band cross talk, which cannot be avoided, is observed through the system's testing [5]. Another nominated example can be reviewed in [21]. The effect of using high gain ROSA limits the US/DS bitrates, the ability to use more channels (i.e., channel spacing), and the BER. To enhance the merged TDM capacity, a high data rate optical source may be used [37]. Finally, the BER enhances to \(10^{-9}\) if the number of channels is reduced to only one (as in this work) [21]. A Long-Reach Bidirectional Centralized WDM-PON system, with attractive operating characteristics, is achieved in [19]. The use of centralized light sources is a desirable solution to reduce system monitoring and maintenance cost [19; 38].