Optimal beamforming for dual-hop MIMO AF relay networks with imperfect CSI

In this study, the authors take into account the imperfect channel state information for beamforming (BF) scheme in a dual-hop multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay network. Since the overall performance has been decided by the signal-to-interference-plus-noise ratio (SINR) at the destination, the authors derive the optimal BF weights that maximise the SINR at the desination. To evaluate the performance of the relay network, the authors also derive closed-form expressions for the outage probability and probability density function of the received SINR. Computer simulations are carried out, which show the superiority of the designed optimal BF scheme, the impacts of channel errors and antenna configurations on the performance of the MIMO AF relay systems, and the validity of the analytical expressions. It is shown that due to the channel errors, the performance of the relay network is bounded no matter how much power is injected into the system.