A Spatial Self-Interference Nullification Method for Full Duplex Amplify-And-Forward MIMO Relays

In full duplex amplify-and-forward (FD-AF) relays, self-interference from the transmit side causes a major problem hindering its commercial spread. To alleviate the front-end saturation problem, we propose a spatial self-interference nullification method employing extra transmit antennas in FD-AF multiple-input-multiple-output (MIMO) relay systems, and analyze characteristics of the proposed system when there exist channel estimation errors. In particular, the probability of relay stability is derived, and the capacity of the relay is analyzed with zero delay assumption. The results indicate that excessive channel estimation errors drive FD-AF relay into unstable modes and cause capacity reduction.