Multiuser MIMO amplify-and-forward relaying schemes with vector precoding

A two-hop multiuser multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay scenario is analyzed in this paper, where the main design challenge resides on the selection of the interdependent precoding and relaying matrices. After analyzing the optimal joint iterative linear design of the precoding and relaying matrices, two simpler non-iterative approaches are proposed and derived: hop-by-hop minimum mean squared error (MMSE) minimization and block diagonal geometric mean decomposition (BD-GMD). The combination of these two techniques and vector precoding (VP) is then proposed to greatly improve the performance of the systems. Provided sim- ulation results prove that the combination of non-linear precoding and simpler matrix design strategies can outperform the optimal and complex joint iterative design with linear transmission.