Joint Beamforming and Power Allocation Design in Cooperative MIMO-NOMA Networks

Due to its improved spectral efficiency, non-orthogonal multiple access (NOMA) is regarded as a promising multiple access technology for beyond fifth-generation (5G) networks. In this paper, we examine the performance of a cell-edge user and suggest a beamforming scheme in a cooperative two-user multiple-input multiple-output (MIMO)-NOMA system with Rayleigh fading channels. In the envisaged scenario, a cell-center user with better channel gain harvests energy and assists a cell-edge user with poorer channel conditions by using a simultaneous wireless information and power transfer mechanism. We first obtain the outage probability expressions in closed form for the cell-edge user for the Kronecker structured channel model in the covariance shaping and indefinite quadratic form. Next, the beamformers at the transmitter and receiver are introduced to reduce outage probability, with transmit beamformers maximizing the signal-to-leakage-plus-noise ratio and receive beamformers minimizing cross-covariance across all users. Furthermore, beamformers are adopted in the two-user network to adjust the power ratio and power allocation coefficients for better performance of the cell-edge user. Moreover, our scheme is also compared with a transmit antenna selection baseline scheme. Simulation results demonstrate that our approach enhances the performance of the two-user cooperative MIMO-NOMA system’s performance, validating the theoretical analysis.