## 3 Results
### Performance Evaluation of Fiber-Wireless Topology  
The performance evaluation of the converged Fiber-Wireless (Fi-Wi) topology supporting the secured P2 MP distribution of symmetric keys via the use of mmWave mesh nodes is depicted in Figure 12.  
It is evident that the key rate behaves in a similar way as in the P2 MP shared fiber configuration of Section 3.2, since the quantum keys are distributed to multiple mmWave nodes through identical fiber segments as in the previous case. That means that all the previous argumentation regarding the maximum transmission distance for the InGaAs- and the CMOS-based photon counters is also true for the hybrid Fi-Wi topology. More specifically, since each mesh node communicates with four mesh clients, the SKR for the Fi-Wi topology serving 16 terminal users (blue lines of Figure 12a,b) is identical to the SKR for the P2 MP shared fiber link serving four users (blue lines of Figure 10a,b). Similarly, the SKR for the Fi-Wi topology serving 64 terminal users (orange lines of Figure 12a,b) is identical to the SKR for the P2 MP shared fiber link serving 16 users (orange lines of Figure 10a,b). At first glance, this hybrid Fi-Wi topology seems preferable respecting the demands of quantum keys for a 5G fronthaul segment, since it offers a reduced number of optical Bob stations required and normally a decrease of the quantum-secured optical link distances which is translated to higher rates. Nevertheless, as described in Section 2.3, the secret keys are used to encrypt the radio controller functions  
Figure 11: QBER\({}_{\text{Raman}}\) and QBER\({}_{\text{dark}}\) for 1, 4, 16 and 64 terminal users, at the maximum propagation distance (i.e., at the point where SKR approaches zero) for each case, for the configuration where the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink, for (**a**) InGaAs; and (**b**) upconverted CMOS-based QKD setups. Figure 12: SKR as a function of fiber length, for the Fi-Wi topology serving \(N=16\) or 64 users, where the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink, for (**a**) InGaAs; and (**b**) upconverted CMOS-based QKD setups. The horizontal lines with different styles correspond to the AES limits for key refresh times equal to 5.14 min (3.7 bps), 1 min (19.2 bps) and 1.4 s (823 bps), respectively. besides the packetized data. According to the documentation by the radio equipment vendor providing information about the encryption in several functions of the radio, three of these functions are encrypted with AES-256 and the other with AES-128 ([59]). Following this list for the needs of our study, we allocate an additional share of the distilled keys for this layer of the controllable mesh node and to recalculate subsequently the lower SKR guaranteeing the key rotation times we have encountered. In more detail, for rotation times equal to 1.4 s, 1 min and 5.14 min, SKRs of at least \((4\times 256+128)\text{bits}/1.4\ s=823\) bps, \((4\times 256+128)\text{bits}/1\ \text{min}=19.2\ \text{bps}\) and \((4\times 256+128)\text{bits}/5.14\ \text{min}=3.7\ \text{bps}\) are required. This increased SKR demands counterbalance, to some extent, the benefits of the hybrid Fi-Wi topology, as shown in Figure 13, where the performance of hybrid topology is compared with the respective of shared optical fiber P2 MP link in the case of distributing keys in a secure way for \(N=64\) terminal users. According to this comparison, the Fi-Wi is slightly favored over the P2 MP topology only for the InGaAs detectors and for the high key rotation time. The reason for that is twofold. Firstly, as mentioned above, apart from the SKR low limits concerning the key demands, the SKR for the Fi-Wi topology serving 64 users is identical to the SKR for the P2 MP shared fiber link serving 16 users.