  This article discusses the positive impact metro cell antennas with narrow
vertical beamwidth and electrical downtilt can have on heterogeneous cellular
networks. Using a model of random cell placement based on Poisson distribution,
along with an innovative 3D building model that quantifies blockage due to
shadowing, it is demonstrated that network spectral efficiency and average user
throughput both increase as vertical beamwidth is decreased and downtilt is
applied to metro cell transmission. Moreover, the network becomes more energy
efficient. Importantly, these additional gains in network performance can be
achieved without any cooperation or exchange of information between macro cell
base stations and metro cells.
