## 5 Results
### Costs Analysis of Evolved FttC Network with New Added Cabinets  
The costs of FttC-based fronthaul using the existing FttC infrastructure only consists in the addition (and installation) of the radio nodes at the distributors. These costs are not considered in the following calculations. Instead, we are interested in the costs of the evolved FttC infrastructure. Figure 8: Sum bit rate coverage for group 1, \(d_{OE}=200\) m—variable of number of pairs per radio node, user activity factor, \(p=0.5\), US with non-vectoring (**a**) and US with vectoring (**b**). Figure 9: Sum bit rate coverage for group 1, \(d_{OE}=200\) m—variable user activity factor \(p\), with and without vectoring: DS (**a**) and US (**b**). We assume they can be calculated as the sum of the following three terms: the (overall) costs of digging to lay optical fiber, the cost for new Cabinets and the cost for the equipment to be installed at the distributor connected by fiber, i.e.,  
\[C_{\text{FttC}}=l_{F}\times c_{F}+n_{C}\times c_{C}+n_{dO}\times c_{d}, \tag{20}\]  
and \(l_{F}\) is the total length of the fiber cables obtained by the sum of the lengths of the optical fiber required to connect the new added Cabinets to the corresponding old Cabinet. The \(c_{F}\) is the unit cost per \(km\) for digging and installing the optical fiber. Considering conventional digging, the typical value for \(c_{F}\) is \(c_{F}\cong\) 60,000 euro per km [12]. Still, in (20), \(n_{C}\) is the total number of new Cabinets to be added to the existing FttC infrastructure and \(c_{C}\) is the cost per single Cabinet which includes all costs for installation. We have assumed \(c_{C}=\) 10,000 euro. Finally, \(n_{dO}\) is the number of distributors to be connected by the optical fiber and \(c_{d}\) is the cost of the G.fast or the optical network termination (ONT) to be installed at the distributor for connecting the radio 5G node. We have assumed \(c_{d}=5000\) euro. The costs of the evolved FttC infrastructure is compared with the cost of a full fiber fronthaul infrastructure where optical fiber is used to connect each distributor to its Cabinet. The formula for evaluating costs in this case is similar to (20) with \(n_{C}=0\) and \(n_{dO}\) equal to the total number of distributors; \(c_{d}\) is the cost of the ONT to be installed at the single distributor and we still assume \(c_{d}=5000\) euro. The \(l_{F}\) is the length of fiber to be deployed and \(c_{dO}\) is un-changed. In Figure 10 we plot the cost of the evolved FttC network as compared to the costs of the all-fiber solution as a function of the distance \(d_{OE}\). Results (in percentage) corresponds to the two options in the previous Section. In both cases, costs tend to increase with \(d_{OE}\) since they are dominated by the digging costs for the optical fiber deployment. With the increase of \(d_{OE}\), costs of the evolved FttC network tend to those corresponding to the all-fiber deployment. The first evolution strategy provides lower cost. However, looking for example at coverage results in Figure 5 cost saving is obtained at the expense of reduced coverage performance as compared with results obtained considering the second strategy for the same \(d_{OE}\). In Figure 10 we observe an inversion of costs with \(d_{OE}\). In particular, for small \(d_{OE}\) the costs of first strategy are higher for group 1 and group 2 with respect to group 3 and then the situation reverses  
Figure 10: Cost for the evolved FttC network. Two evolution options: new Cabinets installed at \(d_{OE}\) (first option, dashed lines), new Cabinets installed at the distance of the first distributor at distance greater or equal to \(d_{OE}\) (second option, solid lines). with the increase of \(d_{OE}\). The inversion of costs still holds for the second strategy even though it occurs for larger \(d_{OE}\) and it is not clearly visible in the Figure. The inversion can be explained considering that the distances of distributors in the group 3 are larger than those in the other groups (see Figure 3).