Millimeter-wave non-orthogonal multiple access systems with sparse antenna arrays

Millimeter wave (mmWave) non-orthogonal multiple access (NOMA) is a multiuser transmission scheme that can increase the quality and data rate of wireless mobile networks. In this article, we introduce an mmWave-NOMA system utilizing a sparse antenna array that not only offers small and lightweight antenna devices in the base station but also improves the outage probability performance of the system. We also introduce a low-complex computation technique to find the optimum beamforming vector to reduce the outage probability. We provide a proof of convexity for the outage probability of the mobiles' communication links in the proposed system for which a gradient-based algorithm can be used to find the optimum solution. The simulation results show that utilizing the proposed optimum beamforming vector reduces the outage probability of the system up to 98% in high signal-to-noise ratios. Our simulation and analysis results demonstrate that the system equipped with a sparse antenna array applying the optimum beamforming vector outperform conventional mmWave-NOMA system with uniform linear array antennas in terms of outage probability and sum rates.