Optimizing Transmission Rate in NOMA via Block Diagonalization Beamforming and Power Allocation

In this paper, we propose a new transmission scheme, relying on user clustering, transmit beamforming and power allocation, for non-orthogonal multiple access (NOMA) in a downlink cellular framework. Assuming that channel state information is available at the base station, the users are first partitioned into small clusters based on a weighted multi-objective optimization, so that each cluster may be served by a single beamforming vector. The complete set of beamforming vectors is jointly designed to remove inter-cluster interference by taking advantage of block diagonalization along with maximum ratio transmission. Subsequently, the NOMA power allocation factors for the users in each cluster are determined by solving an optimization problem, where the aim is to maximize the transmission sum rate subject to power and SINR constraints. The performance of the proposed NOMA scheme is validated by means of numerical analysis. Compared to the benchmark approaches, the results show significant improvements in terms of spectral efficiency and interference cancellation.