  The optimal allocation of time and energy resources is characterized in a
Wireless Powered Communication Network (WPCN) with non-Orthogonal Multiple
Access (NOMA). We consider two different formulations; in the first one
(max-sum), the sum-throughput of all users is maximized. In the second one
(max-min), and targeting fairness among users, we consider maximizing the
min-throughput of all users. Under the above two formulations, two NOMA
decoding schemes are studied, namely, low complexity decoding (LCD) and
successive interference cancellation decoding (SICD). Due to the non-convexity
of three of the studied optimization problems, we consider an approximation
approach, in which the non-convex optimization problem is approximated by a
convex optimization problem, which satisfies all the constraints of the
original problem. The approximated convex optimization problem can then be
solved iteratively. The results show a trade-off between maximizing the sum
throughout and achieving fairness through maximizing the minimum throughput.
