  Although non-orthogonal multiple access (NOMA) is recently considered for
cellular systems, its key ideas such as successive interference cancellation
(SIC) and superposition coding have been well studied in information theory. In
this paper, we overview principles of NOMA based on information theory and
present some recent results. Under a single-cell environment, we mainly focus
on fundamental issues, e.g., power allocation and beamforming for downlink NOMA
and coordinated and uncoordinated transmissions for uplink NOMA.
