On capacity of two-way massive MIMO full-duplex relay systems

In this paper, we consider a one-pair amplify-and-forward relay channel, where two full-duplex users exchange information through a full-duplex relay with a very large number of antennas, while each user only has two antennas. Several power-scaling schemes are proposed based on the maximum-ratio combining/maximum-ratio transmission (MRC/MRT) at the relay. When the number of the relay antennas tends to infinity, we derive and quantify the asymptotic spectral efficiency of the proposed power-scaling schemes. We show that the very large antenna array can significantly reduce the effect of loop interference because of the antenna array gain. Furthermore, the theoretical results indicate that the loop interference can also be reduced by cutting down the transmission power, which is verified by the numerical results. The analytical and numerical results show that the proposed power-scaling schemes can achieve good performance tradeoffs between the spectral efficiency and the energy efficiency.