  The spectrum-efficient millimeter-wave (mmWave) communications has recently
attracted much attention as a viable solution to spectrum crunch problem. In
this work, we propose a novel non-orthogonal multiple access (NOMA) framework,
which makes use of the directional propagation characteristics of mmWave
communications so as to improve the spectral efficiency through non-orthogonal
signaling. In particular, we consider one-bit quantized angle information as a
limited yet effective feedback scheme describing the channel quality of user
equipment (UE) in mmWave bands. The UE pairs for NOMA transmission are then
established using not only the one-bit distance feedback as a classical
approach, but also the one-bit angle feedback. The proposed strategy is
therefore referred to as two-bit NOMA. We also propose a novel hybrid strategy,
called combined NOMA, for the circumstances with no UE pair through two-bit
NOMA. Whenever no UE pair is available through any NOMA strategy, we resort to
single user transmission (SUT) with proper UE selection schemes. The hybrid
sum-rate performance is also analyzed thoroughly with the respective outage and
rate expressions. The numerical results verify that the proposed strategy
outperforms one-bit NOMA schemes with either angle- or distance-only feedback.
