Optimal MIMO transmission with per-antenna power constraints

Many MIMO capacity analyses and precoding algorithms are obtained based on the assumption of total power constraint while assuming power can be allocated freely across antennas. In practical MIMO systems, however, per-antenna power constraints are often more predominant design consideration than the total power constraints. In this paper, we study the transmission schemes for MIMO systems with per-antenna power constraints. We derive the necessary and sufficient conditions for the optimal transmission scheme. We also develop an iterative algorithm and prove its convergence to the optimal solution.