Coordinated Eigen Beamforming for Multi-Pair MIMO Two-Way Relay Network

We consider a multi-pair two-way relay (TWR) network where the multi-antenna users of each pair exchange information via a multi-antenna relay. The interesting challenge is how to deal with the inter- user interference and explore the potential of multiple antennas concurrently. Beamforming methods in previous works are based on the criteria of zero forcing (ZF) and minimum mean square error (MMSE) to mitigate the inter-user interference. However, since the user already knows its own information, it is unnecessary to mitigate the intra-pair interference at the relay. In this paper, we propose a coordinated eigen beamforming (CEB) scheme, which maximizes the effective channel gain of each user in the sub-space nulling the inter-pair interference. The CEB scheme is implemented with an iterative optimization algorithm with limited iterations. Additionally, the power loading scheme is adopted after convergence to guarantee fairness among users. Simulation results indicate our scheme achieves near full diversity order within the sub-space, outperforming pervious works.