Modulation division multiplexing for multiuser diversity beamforming

Multiuser diversity beamforming (MDB) is investigated for downlink channels of multiuser multiple input multiple output (MIMO) systems. In general, the multiple-beam approach for MDB results in a poor performance when the number of users is not sufficiently large. In this paper, we consider a single-beam approach where a common precoder is shared by multiple users using modulation division multiplexing (MDM) of a higher order modulation. Performance criteria for precoder and user selection are derived under the assumption that the maximum likelihood (ML) detector is used.