  A feature of the Internet of Things (IoT) is that some users in the system
need to be served quickly for small packet transmission. To address this
requirement, a new multiple-input multiple-output non-orthogonal multiple
access (MIMO-NOMA) scheme is designed in this paper, where one user is served
with its quality of service (QoS) requirement strictly met, and the other user
is served opportunistically by using the NOMA concept. The novelty of this new
scheme is that it confronts the challenge that most existing MIMO-NOMA schemes
rely on the assumption that users' channel conditions are different, a strong
assumption which may not be valid in practice. The developed precoding and
detection strategies can effectively create a significant difference between
the users' effective channel gains, and therefore the potential of NOMA can be
realized even if the users' original channel conditions are similar. Analytical
and numerical results are provided to demonstrate the performance of the
proposed MIMO-NOMA scheme.
