  We study amplified-and-forward (AF)-based two-way relaying (TWR) with
multiple source pairs, which are exchanging information through the relay. Each
source has single antenna and the relay has multi-antenna. The optimal
beamforming matrix structure that achieves maximum
signal-to-interference-plus-noise ratio (SINR) for TWR with multiple source
pairs is derived. We then present two new non-zero-forcing based beamforming
schemes for TWR, which take into consideration the tradeoff between preserving
the desired signals and suppressing inter-pair interference between different
source pairs. Joint grouping and beamforming scheme is proposed to achieve a
better signal-to-interference-plus-noise ratio (SINR) when the total number of
source pairs is large and the signal-to-noise ratio (SNR) at the relay is low.
