Eigenmode Transmission for the MIMO Broadcast Channel with Semi-Orthogonal User Selection

This paper investigates a low complexity zero-forcing dirty paper coding based transmission approach for the MIMO broadcast channel, employing eigenmode transmission with greedy semi-orthogonal user selection (SUS). We prove that as the number of users K grows large, our scheme achieves the optimal sum rate scaling of the MIMO broadcast channel (i.e. linear scaling with the number of transmit antennas, and double-logarithmic scaling with K). In addition, we show that whilst the number of receive antennas only affects the asymptotic sum rate scaling via the second-order behavior of the multiuser diversity gain; for finite K, the benefit due to multiple receive antennas can be very significant. Finally, we show the interesting result that the semi-orthogonality constraint imposed by the SUS algorithm, whilst facilitating a very low complexity user selection procedure, does not reduce the multiuser diversity gain in either first or second-order.