Hybrid beamforming NOMA for mmWave half-duplex UAV relay-assisted B5G/6G IoT networks

Mobile wireless data collection in beyond 5G (B5G)/6G cellular internet of things (IoT) networks can be achieved by unmanned aerial vehicle (UAV) with high flexible mobility and low cost. In this paper, a half duplex UAV relay is exploited to improve the achievable rate of downlink millimeter-wave (mmWave) massive multi-user multiple-input and multiple-output (MU-MIMO) networks. To improve the spectrum efficiency and mitigate the inter-beam interference, the hybrid beamforming (HB) designs of the base station (BS), the UAV and multiusers are taken into account simultaneously. To maximize the achievable rate from the BS to the multiusers, a two-stage design approach which tries to design the two stages jointly by avoiding the loss of information is proposed. Assuming multiusers are alignment in different beams, the strong effective channel based non-orthogonal multiple access (NOMA) in the power domain is employed to assign power efficiently for each user, thereby increasing the number of users. Simulation results validate the proposed HB-NOMA approach can achieve good achievable rate performance in both uniform linear array and uniform planar array.