Transceiver Optimization for Full-Duplex Massive MIMO AF Relaying With Direct Link

This paper focuses on the end-to-end signal-to-noise ratio (SNR) maximization for full-duplex massive multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay systems in the presence of direct link. First, we rigorously prove the asymptotic optimality of the maximum-ratio combining/maximum-ratio transmission (MRC/MRT) relaying strategy by taking into account the massive MIMO setup. Then, concerning the equivalent optimization problem with respect to source beamformer, we advocate a two-tier iterative algorithm relying on bi-section search, which guarantees a globally optimal solution. As a byproduct of this approach, we show that the optimal source beamformer has an interesting generalized channel matching structure associated with both source-relay and source-destination links. In addition to the optimal design, we devise a high SNR approximation-based suboptimal scheme, which admits a closed-form solution. Simulation results verify the advantage of our full-duplex relaying designs, and also demonstrate a negligible performance gap between the proposed optimal and suboptimal methods.