Joint spatial division and multiplexing — Benefits of antenna correlation in multi-user MIMO

We show that the sum capacity of “spatially well-correlated” Gaussian MIMO broadcast channel (BC) is rather larger than that of the uncorrelated (i.i.d. Rayleigh fading) Gaussian MIMO BC, assuming a special structure of transmit correlation of users. Moreover, a potential sum-rate gap of an ideal correlated Rayleigh fading channel is shown to be M log M over the uncorrelated case, where M is the number of transmit antennas. Finally, we propose a joint spatial division and multiplexing (JSDM) scheme based on opportunistic beamforming that can achieve the optimal multiuser diversity gain with very limited channel state information (CSI) feedback in realistic scenarios, not requiring the special structure of transmit correlation.