Iterative joint MMSE design of relaying MIMO downlink schemes with non-linearly precoded transmission

A two-hop non-regenerative multiuser multiple input multiple output (MIMO) relaying scenario is analysed in this paper, where the main design challenge resides in the selection of the interdependent precoding and relaying matrices. Several linear and non-linear approaches have been proposed for amplify-and-forward (AF) relaying, the best performance being achieved when an iterative joint design approach is followed. We propose the use of non-linear precoding techniques such as Tomlinson-Harashima precoding (THP) and vector precoding (VP) at the downlink transmission with the aim of outperforming the more common linear strategies. Provided simulation results show that the proposed optimum iterative nonlinear precoding schemes outperform the best MIMO-AF relaying architectures in the literature, considering both BER performance and error minimization speed.