Cooperative zero forcing in multi-pair multi-relay networks

In this paper, unidirectional communication between K half-duplex node pairs is considered. The source nodes have N antennas each and the destination nodes have M antennas each. There is no direct link between the source and the destination nodes. Q half-duplex relays, each with R antennas, assist in the communication. It is assumed that the relays do not have enough antennas to spatially separate the data streams and hence, transceive zero forcing cannot be performed at the relays. In this paper, we propose a scheme in which the source nodes and the relays cooperate in choosing their precoding matrices and the filter coefficients, respectively, to perform a cooperative zero forcing. A closed form solution is proposed and the feasibility condition is derived. Simulation results show that the proposed cooperative zero forcing scheme achieves more degrees of freedom and hence, achieves higher sum rate as compared to reference schemes.