User Fairness Non-orthogonal Multiple Access (NOMA) in Millimeter-Wave Communications

Abstract

In this paper, we explore non-orthogonal multiple access in millimeter-Wave communications (mmWave-NOMA). A downlink cellular is considered, where a base station (BS) equipped with a single radio frequency (RF) chain and large antenna arrays serves multiple users with a single antenna. Analog beamforming is utilized to reduce the hardware cost and power consumption. Particularly, we consider the user fairness and formulate a joint beamforming and power allocation problem, which is non-convex. In the propose sub-optimal solution, the closed-form optimal power allocation is first obtained under any fixed beam pattern. Then an approximatively optimal beamforming vector is designed according to the sparsity in the angle domain of the mmWave channel. The achievable rate performance of mmWave-NOMA system is shown to be significantly improved by the proposed approach, compared with the conventional mmWave orthogonal multiple access (mmWave-OMA) system.