  Non-orthogonal multiple access (NOMA) has been considered as a study-item in
3GPP for 5G new radio (NR). However, it was decided not to continue with it as
a work-item, and to leave it for possible use in beyond 5G. In this paper, we
first review the discussions that ended in such decision. Particularly, we
present simulation comparisons between the NOMA and multi-user
multiple-input-multiple-output (MU-MIMO), where the possible gain of NOMA,
compared to MU-MIMO, is negligible. Then, we propose a number of methods to
reduce the implementation complexity and delay of both uplink (UL) and downlink
(DL) NOMA-based transmission, as different ways to improve its efficiency.
Here, particular attention is paid to reducing the receiver complexity, the
cost of hybrid automatic repeat request as well as the user pairing complexity.
As demonstrated, different smart techniques can be applied to improve the
energy efficiency and the end-to-end transmission delay of NOMA-based systems.
