Comparison of zero-forcing methods for downlink spatial multiplexing in realistic multi-user MIMO channels

The use of space-division multiple access (SDMA) in the downlink of a multi-user MIMO wireless communications system can offer a substantial gain in system throughput. We compare the throughput achieved by employing recently developed algorithms for transmit beamforming in multi-user MIMO systems. The block-diagonalization algorithm is a generalization of the channel inversion scheme which suppresses completely all interference among users, although allowing interference among different data streams. The successive optimization algorithm, on the other hand, solves the power minimization problem one user at a time, so that the n-th user produces no interference with respect to the m-th user, where 1≤m\n\n\t\t