Research On Interference Suppression For MIMO Relay Systems

MIMO relay systems have been extensively considered due to the potential benefits of MIMO techniques such as spectral efficiency and link reliability. Unfortunately, the benefits of half-duplex relays(HDR) comes at a price. This is the reduction in bandwidth due to the additional time resource required for transmission and reception. This greatly reduces the benefits that cooperative diversity brings to the relay systems. To recover the throughput loss owing to the additional time resource, full-duplex relays(FDR) and two-path relays(TPR) can receive and transmit simultaneously. However, the self-interference in FDR and the inter-relay interference(IRI) between two relay nodes have a negative effect on the relay performance. It is crucial to suppress the interference to render relay systems feasible.In this paper, the relay employs transmit and receive weight vectors for self-interference suppression. Maximizing the ratio between the power of the useful signal to the self-interference power at the relay reception and transmission and forming a criterion function for jointly calculating the optimal receive and transmit suppression vectors, respectively. Simulation results confirm that the proposed scheme improves the channel capacity and mitigates the self-interference significantly. To reslove the problem of IRI, we study the use of beamforming techniques. We choose the transmit and receive beamforming vectors such that the receive power is minimized from the direction of the other relay and the transmit power is nulled in the direction of the other relay. By choosing the transmit and receive beamforming vectors as the left and the right singular vectors corresponding to the smallest singular value of inter-relay channel matric, we can ensure that the IRI is minimized. Simulation results show that the proposed scheme hasbetter performance than existing approaches.