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 lineofsight (LOS)/non-line-of-sight (NLOS) propagation into 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 distancedependent 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 square of the BS height.