High-sum-rate beamformers for multi-pair two-way relay networks with amplify-and-forward relaying strategy

In multi-pair two-way relay networks, the control over inter-pair-interference is a challenging problem. When mobile stations (MSs) cooperate fully, to achieve the sum capacity of networks and at the same time completely remove the inter-pair-interference, a singular value decomposition (SVD) based beamforming scheme at relay station (RS) is established where SVD beamformers are applied over both uplink and downlink channels, respectively. To avoid any cooperation among users, an efficient beamforming scheme is proposed. This scheme uses the Max-SINR based receive beamformer at RS in uplink channel and the Max-SLNR based transmit precoder at RS in downlink channel. It omits interference (uplink) and leakage (donwlink) inside each pair of users due to their abilities of self-interference cancellation. This beamforming scheme provides an analytical solution like some well-known linear beamformers such as zero-forcing, block diagonalization, etc. From simulation, we find: the proposed SVD shows an excellent sum-rate performance at the expense of a large cooperation overhead at MSs and can be used as a tighter upper bound of sum-rate; the proposed scheme of Max-SINR beamformer plus Max-SLNR precoder performs much better on sum-rate than the ZF-based and the BD-based schemes by using almost the same computational amount.