  This paper investigates the coexistence between two key enabling technologies
for the fifth generation (5G) mobile networks, non-orthogonal multiple access
(NOMA) and millimeter-wave (mmWave) communications. Particularly, the
application of random beamforming to the addressed mmWave-NOMA scenario is
considered in this paper, in order to avoid the requirement that the base
station knows all the users' channel state information. Stochastic geometry is
used to characterize the performance of the proposed mmWave-NOMA transmission
scheme, by using the key features of mmWave systems, e.g., mmWave transmission
is highly directional and potential blockages will thin the user distribution.
Two random beamforming approaches which can further reduce the system overhead
are also proposed to the addressed mmWave-NOMA communication scenario, where
their performance is studied by developing analytical results about sum rates
and outage probabilities. Simulation results are also provided to demonstrate
the performance of the proposed mmWave-NOMA transmission schemes and verify the
accuracy of the developed analytical results.
