This paper analyzes the downlink performance of ultra-dense networks withelevated base stations (BSs). We consider a general dual-slope pathloss modelwith distance-dependent probability of line-of-sight (LOS) transmission betweenBSs and receivers. Specifically, we consider the scenario where each link maybe obstructed by randomly placed buildings. Using tools from stochasticgeometry, we show that both coverage probability and area spectral efficiencydecay to zero as the BS density grows large. Interestingly, we show that the BSheight alone has a detrimental effect on the system performance even when thestandard single-slope pathloss model is adopted.
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