Optimal Beamforming with Combining for the Non-Orthogonal Amplify-and-Forward (NAF) Protocol in Cooperative Communication Systems

This paper expands optimal beamforming with combining from the amplify-and-forward (AF) protocol to the non-orthogonal AF (NAF) protocol for environments with perfect channel state information (CSI) and a sum power constraint. After formulating an optimization problem for maximizing the signal-to-noise ratio (SNR), we propose optimal beamforming and combining vectors. After exhaustive comparison of the optimal beamforming weights with those for the previous results in and the characteristics of the beamforming weights are analyzed according to the protocols and the power constraints. Moreover, it is shown that the optimal combining vector is given succinctly with reduced computational complexity, and that the optimal beamforming could be accomplished using partial CSI. Simulation results verify that the proposed schemes enhance performance.