Transmit Strategies for Rank-Deficient MIMO With Multiple Power Constraints

Abstract

This letter investigates power allocation strategies for multiple-input multiple-output (MIMO) systems under joint sum-power and per-antenna power constraints in the case of rank-deficient channels. Starting from the generic problem, we introduce an auxiliary approach based on a fixed precoder structure, devising a low-complexity solution. Indeed, we derive the closed-form expression for the optimal solution for the considered optimization problem. Then, we present a method to determine the optimal parameter values. Notably, the proposed scheme provides a favorable trade-off between performance and complexity across different MIMO array sizes and medium spatial correlation regimes that model the rank deficiency.