Optimal Joint Source and Relay Beamforming for Parallel MIMO Relay Networks

In this paper, we study the optimal structure of the source precoding matrix and the relay amplifying matrices for multiple-input multiple-output (MIMO) relay communication systems with parallel relay nodes. We show that both the optimal source precoding matrix and the optimal relay amplifying matrices have a beamforming structure. Using the optimal structure, a joint source and relay power loading algorithm is developed to minimize the mean-squared error (MSE) of the signal waveform estimation. Compared with existing algorithms for parallel MIMO relay networks, the proposed joint source and relay beamforming algorithm has a significant improvement in the system bit-error-rate performance.