  Massive multiple-input multiple-output (massive MIMO) and small cell
densification are complementary key 5G enablers. Given a fixed number of the
entire base-station antennas per unit area, this paper fairly compares (i) to
deploy few base stations (BSs) and concentrate many antennas on each of them,
i.e. massive MIMO, and (ii) to deploy more BSs equipped with few antennas, i.e.
small cell densification. We observe that small cell densification always
outperforms for both signal-to-interference ratio (SIR) coverage and energy
efficiency (EE), when each BS serves multiple users via L number of sub-bands
(multi-carrier transmission). Moreover, we also observe that larger L increases
SIR coverage while decreasing EE, thus urging the necessity of optimal 5G
network design. These two observations are based on our novel closed-form SIR
coverage probability derivation using stochastic geometry, also validated via
numerical simulations.
