Multi-cluster MIMO non-orthogonal multiple access for multi-cell systems

In this paper, we present a multi-cluster multiple-input multiple-output non-orthogonal multiple access technique to improve spectral efficiency by simultaneously transmitting multiple data streams to multiple clusters in multi-cell systems. This technique employs receive beamforming matrices for cell-edge users that minimize the multi-cell interference power, irrespective of the number of interfering cells. Based on the receive beamforming matrices, the technique designs transmit beamforming matrices for a serving base station (BS) that eliminate inter-cluster interference (ICI) between cell-edge users and maximize the lower bounds of the received SNRs at the cell-edge users. Then, the technique uses the transmit beamforming matrices to find receive beamforming matrices for cell-center users that eliminate ICI between the cell-center users and maximize the lower bounds of the received SNRs at the cell-center users. This technique does not require channel feedback from the users to the serving BS in order to find all the receive beamforming matrices, thereby reducing system overhead. In addition, based on the transmit and receive beamforming matrices, the proposed technique allocates the transmit power to clusters and users of each cluster in a manner that maximizes the sum rate performance under power constraints supporting fairness between clusters and between users in each cluster. We demonstrate through simulations that the proposed technique achieves better sum rate and outage performances than the existing techniques and can provide a good balance between the performances and the number of clusters simultaneously supported by the serving BS.