Spectral Efficiency Analysis of Two-Way Massive MIMO Full-Duplex Relay Systems with Direct Link

In this paper, we consider a one-pair two-way full-duplex relaying system where two source nodes exchange information with the aid of an amplify-and-forward relay with massive antennas. In this work, we assume the direct link between source nodes is non-negligible and propose a combining scheme, at the destination side, that captures the joint benefit of relay and direct links. First, we drive the communication model and the sum spectral efficiency (SE) of the proposed combining scheme. Then, we quantify the asymptotic expression of SE when the number of antennas at the relay goes to infinity. Asymptotic results show that the transmit power of the source nodes and the relay node have different effect on the asymptotic SE, which is confirmed by numerical results. Using simulations, we also show that, for long packet transmissions, the proposed combining scheme outperforms the classical scheme, where the direct signal is considered as interference at the destination. However, it is not the obvious choice for the short packet transmissions and the transmission where the processing delay at the relay is greater than the packet length.