Fundamental limits in correlated fading MIMO broadcast channels: Benefits of transmit correlation diversity

Abstract

We investigate the impact of transmit correlation on the capacity of correlated fading MIMO broadcast channels (BCs) and establish capacity characterizations in various regimes of system parameters, with a particular interest in the large-scale array (or massive MIMO) regime. It is advocated in this paper that transmit correlation can be of use to increase both multiplexing gain and power gain in multiuser MIMO systems. We show the potential gains and succinctly characterize fundamental limits in correlated fading MIMO BCs, assuming an ideal condition for which transmit correlation diversity is well defined. In particular, transmit correlation is shown to improve the system multiplexing gain up to by a factor of the degrees of transmit correlation diversity. Not relying on the ideal condition on transmit correlations, we further propose a joint spatial division and multiplexing (JSDM) scheme based on opportunistic beamforming that, for a large number of users, can achieve near optimal sum-rate scaling with very limited channel state feedback in realistic channels. Index Terms Multiuser MIMO, transmit antenna correlation, large-scale (massive) MIMO.