Joint Optimal Power Allocation and Beamforming for MIMO-NOMA in mmWave Communications

In this letter, we propose an optimal joint power allocation and beamforming for MIMO-NOMA in mmWave communications. In this method, to reduce the system overhead, we consider a random near random far (RNRF) pairing scheme in our NOMA data transmission. We formulate an optimization problem to find the optimal power allocation and random beamforming (RBF) coefficients to improve the system performance. We prove the convexity of the underlying optimization problem and propose an iterative algorithm to jointly update the power allocation and RBF coefficients to maximize the communication reliability. Our proposed technique significantly reduces the outage probability (OP) of the system.

I. Introduction

With the combination of non-orthogonal multiple access (NOMA) and millimeter wave (mmWave) technology, in addition to spectral efficiency, we can increase the achievable capacity and the data rate of wireless systems [1], [2]. However, mmWave-NOMA systems require the channel state information (CSI) of all users at the base station (BS) to operate properly. This may increase the communication overhead. To address this issue, random beamforming (RBF) has been introduced in the mmWave-NOMA systems to especially support Internet of Things (IoT) and machine-to-machine (M2M) communications [3]–[5].