Iterative transceiver optimization for linear multiuser MIMO channels with per-user MMSE requirements

We address the problem of jointly optimizing linear transmit and receive filters for a multi-user MIMO system, under the assumption that all users have individual Minimum-Mean-Square-Error (MMSE) requirements. Each user can perform spatial multiplexing with several data streams (layers). All users and layers are coupled by interference, so the choice of filters is intricately interwoven with the power allocation strategy. The design goal is to minimize the total power subject to MMSE constraints. This results in a non-convex problem formulation, for which we propose an iterative algorithm. The iteration consists of alternating optimization of powers, transmit filters and receive filters. We prove that the total required power obtained by the algorithm is monotonically decreasing and converges to a limit.