  We investigate on large-scale deployment of non-orthogonal multiple access
(NOMA) for improved spectral and power efficiency in cellular networks to
provide massive wireless connectivity (e.g. for machine-type communication
[mMTC]). First, we describe the basics of single-antenna NOMA technology and
its extension to co-located multiple-antenna NOMA as well as coordinated
multipoint transmission (CoMP)-enabled NOMA technologies. Then we discuss some
of the practical challenges of large-scale deployment of NOMA such as the
inter-NOMA-interference (INI), inter-cell interference, and hardware
implementation complexity. To this end, we present one key enabling technique
to overcome the challenges of large-scale deployment of NOMA. Generally
speaking, for a feasible large-scale NOMA implementation, sophisticated
diversity enhancing techniques can be used to compensate for the degradation in
coding gain and to decrease the complexity resulting from excessive INI and
increased level of required successive interference cancellation (SIC).
Furthermore, to massively extend NOMA over the network coverage area, NOMA
transmitters have to cooperate in a generalized manner to serve all nearby
users simultaneously.
