Joint precoding and beamforming design for the downlink in a multiuser MIMO system

Assuming perfect channel knowledge at the transmitter, we study space-time beamforming for the downlink in a multiuser multi-input multi-output (MIMO) channel while a nonlinear interference pre-cancellation is presumed at the transmitter. The antenna arrays may be employed at both the transmitter and the receivers. The optimum transmit/receive beam vectors are obtained based on a minimum mean-squared error (MMSE) criterion and a per-user power constraint. In frequency selective fading channels, where orthogonal frequency division multiplexing (OFDM) is applied, the precoding and beamforming design is extended over space and frequency dimensions as well. In fact the proposed algorithm offers a unique method for assigning frequency bins in a MIMO-OFDMA system. The bit error rate performance of the proposed algorithm is assessed by computer simulations.