  Non-orthogonal multiple access (NOMA) is potentially capable of circumventing
the limitations of the classic orthogonal multiple access schemes, hence it has
recently received significant research attention both in industry and academia.
This article is focused on exploiting multiple antenna techniques in NOMA
networks, with an emphasis on investigating the rate region of multiple-input
multiple-output (MIMO)-NOMA, whist reviewing two popular multiple antennas
aided NOMA structures, as well as underlining resource management problems of
both single-carrier and multi-carrier MIMO-NOMA networks. This article also
points out several effective methods of tackling the practical implementation
constraints of multiple antenna NOMA networks. Finally, some promising open
research directions are provided in context of multiple antenna aided NOMA.
