SINR Balancing for the Multi-User Downlink under General Power Constraints

We address the problem of maximizing the minimum signal to interference and noise ratio of individual users via linear preceding in a multiuser downlink channel with multiple antennas at the transmitter and single antenna receivers. While previous research aimed at optimizing transmission under a total power constraint over all antennas, we provide a framework for solving the optimization under power constraints per arbitrary groups of antennas. The results include power constraints per antenna as well as a sum-power constraint as special cases. The scenario is motivated by recent interest in so called network- MIMO techniques where mobile terminals may be served by multiple base stations subjected to individual power constraints.