Multiuser diversity beamforming for downlink channels using modulation division multiplexing

Multiuser diversity beamforming (MDB) is investigated for downlink channels of multiuser multiple input multiple output (MIMO) systems. Since the use of multiple beams simultaneously results in a poor performance of MDB when the number of users is not sufficiently large, the use of single-beam at a time is considered to avoid performance degradation due to the interference from other beams. Furthermore, in order to share a common precoder by multiple users, modulation division multiplexing (MDM) with a higher order modulation for MDB is discussed. Performance criteria for precoder and user selection are derived under the assumption that the maximum likelihood (ML) detector is used.