# Optical Channel Selection Avoiding DIPP in DSB-RFoF Fronthaul Interface
## 2 System, Methods, and Network Components
### Fiber-Optic Fronthaul Path  
The fiber-to-the-antenna (FTTA) architecture is used in the basic solutions for connecting the DU and RU. In this case, the optical path is homogeneous, and no active devices are used along the path. In the extended version of the FTTA link, a passive optical network (PON) can be used, which causes a deterioration of the optical power balance due to the presence of high loss optical splitters, but it enables the use of the already existing resources of the optical network. The Xhaul is a universal extension of the optical fiber network with active and reconfigurable devices. The radio signal traveling over the all-optical path will reach optical fiber sections with different propagation properties. At this point, choosing the right optical carrier is crucial. Three generations of single-mode telecommunications optical fibers are used for the calculations and simulations. The most common single-mode fiber standard is ITU-TG.652D [41]. It has a wide range of single modality versus wavelength. Its counterpart in the version resistant to macro-bending is the fiber of the ITU-T G.657A standard [42]. This is an SMF fiber that is increasingly replacing the fibers of the G.652D standard. ITU-T G.655 fiber cables are often used in DWDM systems [43]. These fibers have a narrower range of single modality as a function of wavelength, due to adjustments related to DWDM standardization. The standard defined in two tables, i.e., G.655D and G.655E, are used for calculations. Table 1 shows the standard and maximum attenuation coefficients of single-mode optical fibers, which were used to determine a more precise absorption characteristic as a function of wavelength [41; 42; 43; 44] (Figure 2). Parameters \(D\) and \(S\) were used to model the delay characteristics of the modulated signals. In order to determine the averaged characteristics of the chromatic dispersion coefficient \(D\) of the G.652D and G.657A standards, the Sellmeier polynomials included in the recommendations [42; 43] were used:  
\[D_{\text{G.652/G.657}}=\left\{ \begin{array}{ll}\frac{\frac{3\lambda_{\text{ min}}}{4}\left[1-\left(\frac{3\text{min}}{4}\right)^{4}\right]+\frac{3\lambda_{ \text{min}}}{4}\left[1-\left(\frac{3\text{min}}{4}\right)^{4}\right]}{2}&\text {for 1260 nm }\leq\lambda\leq 1300\:\text{nm}\\ \frac{\frac{3\lambda_{\text{min}}}{4}\left[1-\left(\frac{3\text{min}}{4} \right)^{4}\right]+\frac{3\lambda_{\text{min}}}{4}\left[1-\left(\frac{3\text {min}}{4}\right)^{4}\right]}{2}&\text{for 1300 nm }<\lambda\leq 1324\:\text{nm}\\ \frac{\lambda_{\text{min}}\left[1-\left(\frac{3\text{min}}{4}\right)^{4} \right]+\frac{3\lambda_{\text{min}}}{2}\left[1-\left(\frac{3\text{min}}{4} \right)^{4}\right]}{2}&\text{for 1324 nm }<\lambda\leq 1460\:\text{nm}\\ 0.06\cdot\left(\lambda-1460\right)+10.5485&\text{for 1460 nm }<\lambda\leq 1625\:\text{nm}\end{array} \right. \tag{1}\]  
where \(\lambda_{\text{0 min}}=1300\:\text{nm}\), \(\lambda_{\text{0 max}}=1324\:\text{nm}\), \(S_{\text{0 min}}=0.073\:\text{ps/nm}^{2}\cdot\text{km}\), and \(S_{\text{0 min}}=0.092\:\text{ps/nm}^{2}\cdot\text{km}\). The characteristics of the chromatic dispersion coefficient \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fiber** & **1310 nm** & **1380 nm** & **1550 nm** & **1625 nm** \\ \hline G.652D/G.657A—std & 0.33 dB/km & 0.31 dB/km & 0.20 dB/km & 0.25 dB/km \\ G.652D/G.657A—max 1 & 0.40 dB/km & 0.4 dB/km & 0.4 dB/km & 0.3 dB/km & 0.4 dB/km \\ G.655D/E—std & - & - & 0.22 dB/km & 0.27 dB/km \\ G.655D/E—max 2 & - & - & 0.35 dB/km & 0.4 dB/km \\ \hline \hline \end{tabular} 1
[FOOTNOTE:1]Footnote 1: According to recommendations [41; 42]. 2  
\end{table} 
Table 1: Empirical and usually measured single-mode optical fiber attenuation coefficients [44]. Figure 2: Modeled attenuation characteristics of single-mode optical fibers in range of single-modality limited by the cut-off wavelength [41; 42; 43].