  Two key traits of 5G cellular networks are much higher base station (BS)
densities - especially in the case of low-power BSs - and the use of massive
MIMO at these BSs. This paper explores how massive MIMO can be used to jointly
maximize the offloading gains and minimize the interference challenges arising
from adding small cells. We consider two interference management approaches:
joint transmission (JT) with local precoding, where users are served
simultaneously by multiple BSs without requiring channel state information
exchanges among cooperating BSs, and resource blanking, where some macro BS
resources are left blank to reduce the interference in the small cell downlink.
A key advantage offered by massive MIMO is channel hardening, which enables to
predict instantaneous rates a priori. This allows us to develop a unified
framework, where resource allocation is cast as a network utility maximization
(NUM) problem, and to demonstrate large gains in cell-edge rates based on the
NUM solution. We propose an efficient dual subgradient based algorithm, which
converges towards the NUM solution. A scheduling scheme is also proposed to
approach the NUM solution. Simulations illustrate more than 2x rate gain for
10th percentile users vs. an optimal association without interference
management.
