MED Precoding for Multiuser MIMO-NOMA Downlink Transmission

In this paper, the design of minimum Euclidean distance (MED) precoders is developed for multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) downlink. First, we propose the MED precoding algorithm for the two-user 2x2 MIMO-NOMA downlink by combining the methodology of MED precoding previously developed for unicast MIMO and multicast MIMO scenarios. Then, to extend MED precoders to general multiuser scenarios, we propose two algorithms for user pairing, based on the condition number and orthogonality defect, respectively. Finally, computer simulations validate the effectiveness of the proposed MED precoders as well as the user pairing algorithms.