A New Method of MIMO-Based Non-Orthogonal Multiuser Downlink Transmission
In this paper, we propose a new method for nonorthogonal multiuser downlink transmission, referred to as multiple-input multiple-output lattice partition multiple access (MIMO-LPMA). The new method is based on the combination of user selection, zero forcing beamforming, and LPMA, and it uses N base station antennas to deliver information to N clusters of M users each. The method thus accommodates a total of NxM users on a given time/frequency resource in a non-orthogonal fashion. The user selection algorithm ensures that all users in each cluster are sufficiently aligned with their respective transmission beam. Zero forcing beamforming controls the inter-cluster crosstalk, ensuring that beams transmitted to different clusters do not interfere to one another. LPMA encoding and decoding allows to superimpose and separate multiple messages on the same beam. Simulations show that the proposed MIMO-LPMA method outperforms the conventional approach based on non-orthogonal multiple access (MIMO-NOMA) in terms of achievable rates. In particular, our results indicate that MIMO-LPMA guarantees a significantly larger 95%-likely rate.