Low-Resolution Limited Feedback for mmWave NOMA Communications

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 numerical results verify that the respective transmission scheme, which is referred to as two-bit NOMA, outperforms the sum-rate performance of angle- or distance-only one-bit NOMA schemes. We also investigate impact of the quantization threshold and size of the user region on the overall sum rate performance, which reveal the practical circumstances making the proposed two-bit NOMA a promising strategy.