Optimizing the spectral efficiency of multiuser MIMO smart antenna systems

Over the years, several smart antenna systems have been proposed and demonstrated in wireless communications systems, and these have shown that significant system performance improvement is possible. In this paper, we consider the maximization of the spectral efficiency of a multiuser MIMO system for downlink communications (one base to many mobiles) in both frequency flat and selective fading channels. Each mobile (user) in the system incorporates an array of n_R antennas and in general transmits K_m⩾1 space-time subchannels, in the same frequency spectrum and time slot. Our objective is to jointly find the antenna weights for all the users, under the constraint of fixed transmit power, so that the spectral efficiency of the system (or the average spectral efficiency per user) is maximized. An iterative procedure that successively nulls out all the broadcast interference is proposed, and simulation results show that multiuser MIMO optimization significantly outperforms single-user MIMO optimization. In addition, spectral efficiency close to an upper bound can be achieved