On the Beamforming Design and Transmit Power Analysis for Single- and Multi-Cluster NOMA

This paper is on the beamforming design and performance analysis of the power-domain non-orthogonal multiple access (NOMA) systems. First, a closed-form linear beamforming design is proposed for single-cluster NOMA systems with two users to minimize the required transmit power with users' signal-to-interference-plus-noise-ratios (SINRs) guaranteed. The average power consumption and the power scaling law are derived for the proposed beamforming design. For multi-cluster NOMA, we exploit a two-stage beamforming design where the first stage eliminates the inter-cluster interference via zero-forcing (ZF) and the second stage aims at saving the required transmit power within each cluster by using the proposed single-cluster beamforming design based on the effective channel vectors. Numerical results are provided to show the superiority of NOMA transmissions with our proposed beamforming comparing to other transmission schemes in terms of the required transmit power and the outage performance.