Robust Tomlinson-Harashima precoding design in amplify-and-forward MIMO relay systems via MMSE criterion

This paper addresses the problem of robust Tomlinson-Harashima precoding (THP) for multiple-input multiple-output (MIMO) relay systems. The robust nonlinear transceiver design consists of a TH precoder at the source along with a linear precoder at the relay and an minimum-mean-squared-error (MMSE) receiver at the destination. The imperfect channel state information (CSI) is considered. By taking the channel uncertainties into account, the source and relay precoders are jointly optimised to minimise the mean-squared-error (MSE).We finally use an iterative method to obtain the solution for relay and source precoders via Karush-Kuhn-Tucker (KKT) conditions. Simulation results demonstrate that the proposed scheme outperforms existing transceiver designs with perfect and imperfect CSI.