Non-Regenerative Multicarrier MIMO Relay Communications Based on Minimization of Mean-Squared Error

In this paper we propose non-regenerative multi-carrier multiple-input multiple-output (MIMO) relay techniques that minimize the mean-squared error (MSE) of the signal waveform estimation. We establish the closed-form optimal precoding matrices at the source and relay nodes in the absence of the direct source-destination link. Interestingly, we show that the proposed precoding matrices jointly convert the multicarrier MIMO relay channel into parallel single-input single-output (SISO) relay channels. In order to reduce the computational complexity of the optimal algorithm, a suboptimal precoding approach based on an upper-bound of the MSE expression is developed. Numerical examples illustrate a significant performance improvement of the proposed algorithms over the existing techniques.