Joint combiner and precoding in MU-MIMO downlink systems with limited feedback and user selection

In this paper, we propose an improved transmission scheme for multiuser multiple-input multiple-output (MU-MIMO) downlink systems with limited feedback, in which the joint use of the receive antenna combiner with both transmit precoding and user selection is essential. In this scheme, each user independently feeds back the index of its preferred-beam vector and an ideal scalar denoting its estimated signal-to-interference-plus-noise ratio (SINR), respectively. Utilizing the received feedback information, base station (BS) can easily generate the precoding matrix by zero-forcing (ZF) or minimum mean-square error (MMSE) criterion. In addition, a user selection algorithm is presented to exploit multiuser diversity for the cases that the number of users exceeds that of transmit antennas. Numerical results show that the proposed transmission scheme improves the sum-rate performance of MU-MIMO downlink systems and verify its effectiveness.