Downlink Cellular Network Analysis with LOS/NLOS Propagation and Elevated Base Stations

In this paper, we investigate the downlink performance of dense cellular networks with elevated base stations (BSs) using a channel model that incorporates line-of-sight (LOS)/non-line-of-sight (NLOS) propagation in both small-scale and large-scale fading. Modeling LOS fading with Nakagami-$m$ fading, we provide a unified framework based on stochastic geometry that encompasses both closest and strongest BS association. Our study is particularized to two distance-dependent LOS/NLOS models of practical interest. Considering the effect of LOS propagation alone, we derive closed-form expressions for the coverage probability with Nakagami-$m$ fading, showing that the performance for strongest BS association is the same as in the case of Rayleigh fading, whereas for closest BS association it monotonically increases with the shape parameter $m$. Then, focusing on the effect of elevated BSs, we show that network densification eventually leads to near-universal outage even for moderately low BS densities: in particular, the maximum area spectral efficiency is proportional to the inverse of the squared BS height.