  With the severe spectrum shortage in conventional cellular bands, millimeter
wave (mmW) frequencies between 30 and 300 GHz have been attracting growing
attention as a possible candidate for next-generation micro- and picocellular
wireless networks. The mmW bands offer orders of magnitude greater spectrum
than current cellular allocations and enable very high-dimensional antenna
arrays for further gains via spatial multiplexing. However, the propagation of
mmW signals in outdoor non line-of-sight (NLOS) links remains challenging and
the feasibility of wide-area mmW cellular networks is far from clear. This
paper uses recent real-world measurements at 28 GHz in New York City to provide
a realistic assessment of mmW picocellular networks in a dense urban
deployment. It is found that, even under conservative propagation assumptions,
mmW systems with cell radii of 100m can offer an order of magnitude increase in
capacity over current state-of-the-art 4G cellular networks with similar cell
density. However, it is also shown that such mmW networks may operate in a
largely power-limited regime where the full spatial and bandwidth degrees of
freedom are not fully utilized. This power-limited regime contrasts
significantly with current bandwidth-limited cellular systems, requiring
alternate technologies for mmW systems that may unlock further gains that mmW
frequency bands offer.
