Considerations on Tradeoff Between Downlink NOMA and Beamforming in Mobile Systems

Non-orthogonal multiple access (NOMA) is a potential candidate for increasing the spectral efficiency for fifth-generation (5G) mobile systems. Beamforming is established to improve data rates and/or extend cell coverage in 5G mobile systems. However, the user throughput performance using downlink NOMA and beamforming together has not been sufficiently evaluated. In this paper, we evaluate the user throughput of mobile systems using downlink NOMA and beamforming as a function of the number of transmission (Tx) beams, using system-level computer simulations. From these results, we discuss the tradeoff between downlink NOMA and beamforming. Specifically, we confirm that the use of downlink NOMA and beamforming together can increase the user throughput, however the improvement rate of downlink NOMA decreases as the number of Tx beams increases.