Sum Rate Maximization of MIMO Broadcast Channels with Coordination of Base Stations

We consider cooperative downlink transmission in multiuser, multi-cell and multiple-antenna cellular networks. It has been shown that multi-base coordinated transmission has significant spectral efficiency gains over that without coordination. The capacity limits can be achieved using a non-linear preceding technique known as dirty paper coding, which is still infeasible to implement in practice. This motivates investigation of a simpler linear preceding technique based on generalized zero-forcing known as block diagonalization (BD). In this paper, an enhanced form of BD is proposed for multiple-input multiple-output (MIMO) multi-base coordinated network. It involves optimizing the precoding over the entire null space of other users´ transmissions. The performance limits of the multiple-antenna downlink with multi-base coordination are studied using duality of MIMO broadcast channels (BC) and MIMO multiple-access channels (MAC) under per-antenna power constraint, which has been established recently.