Loop interference suppression in full-duplex MIMO relays based on space projection

Full-duplex MIMO relays can provide cost-effective coverage and higher spectral efficiency, but simultaneous reception and transmission in the same frequency band could make relays prone to oscillate. Because the loop back channel response matrix is frequently full rank, conventional spatial loop interference suppression techniques using receive and transmit filters are not feasible. This paper presents an algorithm which uses the null space projection and subspace projection to enhance the loop interference mitigation. Meanwhile, the multipath propagation of loop interference channel is also taken into account. Analysis and simulation proved that the proposed algorithm outperforms conventional algorithms. Especially, even though the loop back channel matrix is full rank, the proposed algorithm can still completely suppress the loop interference.