Linear Transceiver Design for SINR Balancing in MIMO Downlink Channels

We consider a single-cell multiple-input multiple-output (MIMO) downlink channel where linear transmission and reception strategy is employed. The base station (BS) transmitter is equipped with a scheduler using a simple opportunistic beamforming strategy, which associates an intended user for each of the transmitted data streams. For the case when the channel of the scheduled users is available at the BS, we propose a joint power control and linear transmit and receive beamformers design to optimally balance the SINR values of data streams under a total power budget. The proposed method can handle multiple antennas at the BS and at the mobile users with single and/or multiple data streams per scheduled user. We consider a general problem formulations which includes minimum SINR constraints on a subset of data streams and discuss possible particularizations which can be solved more efficiently. By exploiting the uplink-downlink SINR duality, we decompose the original optimization problem as a series of remarkably simpler optimization problems which can be efficiently solved by using standard convex optimization solvers. The simulations show that the algorithm converges fast to a solution, which can be a local optimum, but is still efficient. Only one iteration of the proposed method is enough to substantially outperform the zero forcing based solution.