## 3 Numerical Results
### OP Dependence on the MCF Length  
The dependence of the OP on the MCF length, for one interfering core, \(r=0.1\), \(|S_{mn}\cdot R_{s}|=0.01\) and \(|S_{mn}\cdot R_{s}|=1000\), and several ICXT levels, is studied in the following. The objective is to analyze the effect of the ICXT in the case of electrical noise dominance (short MCF length) and ASE noise dominance (long MCF length). Hence, the ICXT level is set independent of the MCF length.  
Figure 2 shows the OP as a function of the ICXT level, for \(r=0.1\), \(|S_{mn}\cdot R_{s}|=0.01\) and \(|S_{mn}\cdot R_{s}|=1000\), and \(L\)=10 km, \(L\) = 40 km and \(L\) = 80 km. In Figure 2, with \(|S_{mn}\cdot R_{s}|=1000\), longer MCF lengths lead to a higher tolerance to ICXT, while, for \(|S_{mn}\cdot R_{s}|=0.01\), the tolerated ICXT level is not particularly affected by the different noise regimes. These results suggest that, with \(|S_{mn}\cdot R_{s}|=1000\), the difference between the dominance of signal-ASE beat noise on the performance with 80 km-long MCF, and the enhanced contribution of electrical noise to the performance, for 10 km-long MCF, may influence the tolerance to ICXT.  
Figure 3 shows the maximum acceptable ICXT level required to achieve OP = \(10^{-3}\) and OP = \(10^{-4}\) as a function of the MCF length, with \(r=0.1\), for \(|S_{mn}\cdot R_{s}|=0.01\) and \(|S_{mn}\cdot R_{s}|=1000\). Figure 3 extends the conclusions taken from Figure 2 to other MCF lengths. In Figure 3, for \(|S_{mn}\cdot R_{s}|=0.01\), the ICXT level required to achieve the OPs of \(10^{-3}\) and \(10^{-4}\) varies slightly less than 0.5 dB, with the MCF length increase. For \(|S_{nm}\cdot R_{s}|=1000\), the maximum acceptable ICXT level required to achieve OPs of \(10^{-3}\) and \(10^{-4}\) increases with the MCF length increase, showing an increase of 0.8 dB and 1.4 dB from 10 km to 40 km and 80 km, respectively. These results may be explained by the way how chromatic dispersion from the MCF and DCF affects the ICXT mechanism and also by the noise dominance regime for the different link lengths.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Value** \\ \hline Operating wavelength & \(\lambda_{0}=1550\) nm \\ Symbol rate & \(R_{s}=56\) Gbaud \\ Receiver electrical filter bandwidth & \(B_{e,RX}=0.85\times R_{s}\) \\ Receiver optical filter bandwidth & \(B_{o}=1.6\times R_{s}\) \\ Number of generated PAM4 symbols in each MCF realization & \(4^{4}\) \\ EDFA noise figure & \(4.77\) dB \\ Optical filter insertion loss & \(i_{L}=1\) \\ Number of PMPs & \(N_{p}=1000\) \\ Interfering core power splitting & \(\xi_{m}=0.5\) \\ Number of interfering cores & \(N_{l}=1,2,4\) \\ Skew-symbol rate product & \(|S_{mn}\cdot R_{s}|=0.01\), \(|S_{mn}\cdot R_{s}|=1000\) \\ MCF chromatic dispersion parameter & \(D_{\lambda,n}=17\) ps/(nm km) \\ MCF attenuation coefficient & \(\alpha=0.2\) dB/km \\ DCF chromatic dispersion parameter & \(D_{\lambda,DCF}=-100\) ps/(nm km) \\ DCF attenuation coefficient & \(\alpha_{DCF}=0.5\) dB/km \\ PIN responsivity & \(R_{\lambda}=1\) A/W \\ BER limit in the presence of ICXT & \(3.8\times 10^{-3}\) \\ BER in the absence of ICXT & \(3.8\times 10^{-5}\) \\ \hline \end{tabular}
\end{table}
Table 1: System and simulation parameters.  
Furthermore, for 80 km and OP \(=10^{-4}\), a higher tolerance to ICXT exceeding 8.1 dB is observed for high SSRP in comparison with low SSRP. A similar higher tolerance to ICXT for high SSRP has been found in other works [22; 25]. For \(|S_{mn}\cdot R_{s}|=1000\), several hundreds of PAM4 symbols in the interfering core contribute to ICXT, which induces a \"noise\"-like behavior on the signal received in the CUT, and reduces the ICXT impact. For \(|S_{mn}\cdot R_{s}|=0.01\), only one PAM4 symbol in the interfering core contributes to ICXT, and well-defined amplitude levels due to interference are created on the received eye-pattern of the signal received in the CUT. This increases the ICXT impact on the system performance.