# Performance Assessment and Comparison of Deployment Options for 5G Millimeter Wave Systems
## 4 Numerical Results
### Coverage Metrics
For less than 16 element links from the BS to the UE, directly or via a terrestrial re-transmitter, very small changes of about 200 m are experienced, while, in the case of the aerial re-transmitter, it reaches 500 m. The plot in Figure 3(a) for \(P_{0}\leq 0.02\) stays at 0 because it is impossible to reach the UE from the aerial re-transmitter location with the given outage probability and a number of antenna elements. This is also reflected in Figure 3(b), where the link between UAV-UE starts from this point. Since the resulting coverage is a sum of the link coverages, we have a sharp rise in Figure 3(a). Similar behavior can be seen in Figure 3(a), where, for the UAV-UE link and \(P_{0}=0.01\), the plot starts only from 36 antenna elements. This is also due to the fact that, with fewer elements, it is impossible to reach the UE with a given outage probability. The fact that the plot does not slowly rise  
Figure 3: Single BS coverage as a function of deployment option. from 0, as it does in Figure 4b, is because the number of elements is a discrete parameter, resulting in the plot involving a stair-step. Interestingly, the UAV-UE and Terr-UE nodes are characterized by approximately the same coverage despite the difference between the terrestrial and UAV IAB node deployments. A plausible explanation is that the height of the terrestrial IAB node (10 m) is already high enough to mitigate dynamic human body blockage situations, while impairments induced by the IAB node height are very similar due to the low height of the UE. Thus, we can conclude that the height of the lowest communications entity is the one defining the coverage radius of a link. The final intermediate metric affecting the BS deployment density is the end-to-end spectral efficiency and the spatial spectral efficiency illustrated in Figure 5b and Figure 5a, respectively, for an end-to-end outage probability \(P_{0}=0.1\). By analyzing the spectral efficiencies, we observe that the difference between deployment options is almost unnoticeable. The rationale is that all of them include a link to the UE that is heavily affected by both dynamic human body blockage and building blockage and determines the end-to-end spectral efficiency. However, as can be seen in Figure 5b, the difference in spatial efficiency is drastic, with the BS-UAV-UE option characterized by the least performance. Interestingly, the use of terrestrial BS in the BS-Terr-UE deployment option is characterized by the highest possible performance despite having a large coverage, as demonstrated in Figure 3. This terrestrial deployment is a natural trade-off between the coverage and the aggregate rate. Finally, concluding the numerical results, we assess the required density of the BS in Figure 6. Here, Figure 6a shows the BS density for two end-to-end outage probabilities 0.1 and 0.01, while Figure 6b illustrates it for antenna arrays utilized at the link to the BS. Analyzing the data, one may observe that the required BS density depends heavily on the antenna array and outage. For a smaller number of elements, e.g., 20-40, the difference in the BS density between end-to-end outage 0.1 and 0.01 reaches 2-3 times, while, for a  
Figure 4: Coverage as a function of outage probability. Figure 5: Spectral and spatial efficiencies of the considered deployment options. higher number of elements, e.g., 100-120, all the deployments are principally similar in terms of BS density. From the analysis provided, one can see that, although implementing UAVs as relays gives great benefits, nevertheless, these benefits have their own limitations. As was shown in this section, UAVs have a much higher outage probability than terrestrial relays with the same number of antenna elements. This limitation can be mitigated by using antennas with more elements; however, it would also impact the cost of such a system. However, with similar antennas, all the other parameters are much higher than those of terrestrial relays and direct connection.