  The near-far problem causes severe throughput unfairness in wireless powered
communication networks (WPCN). In this paper, we exploit non-orthogonal
multiple access (NOMA) technology and propose a fairness-aware NOMA-based
scheduling scheme to mitigate the near-far effect and to enhance the max-min
fairness. Specifically, we sort all users according to their channel conditions
and divide them into two groups, the interference group with high channel gains
and the noninterference group with low channel gains. The power station (PS)
concurrently transmits energy signals with the data transmissions of the users
in the interference group. Thus, the users in the noninterference group can
harvest more energy and achieve a higher throughput, while the users in the
interference group degrade their performance due to the interfering signals
from the PS. We then apply order statistic theory to analyze the achievable
rates of ordered users, based on which all users are appropriately grouped for
NOMA transmission to achieve the max-min fairness of the system. Meanwhile, the
optimal number of interfered users that determines the set of users in each
group, is derived. Our simulation results validate the significant improvement
of both network fairness and throughput via the fairness-aware NOMA-based
scheduling scheme.
