Abstract
In this letter, we examine the impact of the elevated base stations (BSs) on the performance of ultra-dense networks (UDNs). To this end, we first model the channel between an elevated BS and typical user equipment as a 3-D probabilistic line-of-sight channel by considering the height of BSs. Using stochastic geometry, we then derive the expression for the coverage probability of our considered UDNs. Finally, through numerical results, we show how the coverage probability can be maximized by judiciously selecting the height and the density of BSs. The results reported here provide insights into the deployment of BSs in the UDNs.