  This article presents advances in resource allocation (RA) for downlink
non-orthogonal multiple access (NOMA) systems, focusing on user pairing (UP)
and power allocation (PA) algorithms. The former pairs the users to obtain the
high capacity gain by exploiting the channel gain difference between the users,
while the later allocates power to users in each cluster to balance system
throughput and user fairness. Additionally, the article introduces the concept
of cluster fairness and proposes the divideand- next largest difference-based
UP algorithm to distribute the capacity gain among the NOMA clusters in a
controlled manner. Furthermore, performance comparison between multiple-input
multiple-output NOMA (MIMO-NOMA) and MIMO-OMA is conducted when users have
pre-defined quality of service. Simulation results are presented, which
validate the advantages of NOMA over OMA. Finally, the article provides avenues
for further research on RA for downlink NOMA.
