  In overloaded Massive MIMO systems, wherein the number K of user equipments
(UEs) exceeds the number of base station antennas M, it has recently been shown
that non-orthogonal multiple access (NOMA) can increase performance. This paper
aims at identifying cases of the classical operating regime K < M, where
code-domain NOMA can also improve the spectral efficiency of Massive MIMO.
Particular attention is given to use cases in which poor favorable propagation
conditions are experienced. Numerical results show that Massive MIMO with
planar antenna arrays can benefit from NOMA in practical scenarios where the
UEs are spatially close to each other.
