  In this paper, we study the downlink performance of two important 5G network
architectures, i.e. massive multiple-input multiple-output (M-MIMO) and
small-cell densification. We propose a comparative modeling for the two
systems, where the user and antenna/base station (BS) locations are distributed
according to Poisson point processes (PPPs). We then leverage both the
stochastic geometry results and large-system analytical tool to study the SIR
distribution and the average Shannon and outage rates of each network. By
comparing these results, we observe that for user-average spectral efficiency,
small-cell densification is favorable in crowded areas with moderate to high
user density and massive MIMO with low user density. However, small-cell
systems outperform M-MIMO in all cases when the performance metric is the
energy efficiency. The results of this paper are useful for the optimal design
of practical 5G networks.
