  Non-orthogonal multiple access (NOMA) has attracted much recent attention
owing to its capability for improving the system spectral efficiency in
wireless communications. Deploying NOMA in heterogeneous network can satisfy
users' explosive data traffic requirements, and NOMA will likely play an
important role in the fifth-generation (5G) mobile communication networks.
However, NOMA brings new technical challenges on resource allocation due to the
mutual cross-tier interference in heterogeneous networks. In this article, to
study the tradeoff between data rate performance and energy consumption in
NOMA, we examine the problem of energy-efficient user scheduling and power
optimization in 5G NOMA heterogeneous networks. The energy-efficient user
scheduling and power allocation schemes are introduced for the downlink 5G NOMA
heterogeneous network for perfect and imperfect channel state information (CSI)
respectively. Simulation results show that the resource allocation schemes can
significantly increase the energy efficiency of 5G NOMA heterogeneous network
for both cases of perfect CSI and imperfect CSI.
