  A full-duplex two-way relay channel with multiple antennas is considered. For
this three-node network, the beamforming design needs to suppress
self-interference. While a traditional way is to apply zero-forcing for
self-interference mitigation, it may harm the desired signals. In this paper, a
design which reserves a fraction of self-interference is proposed by solving a
quality-of-service constrained beamforming design problem. Since the problem is
challenging due to the loop self-interference, a convergence-guaranteed
alternating optimization algorithm is proposed to jointly design the relay-user
beamformers. Numerical results show that the proposed scheme outperforms
zero-forcing method, and achieves a transmit power close to the ideal case.
