On the Beamforming Design for MIMO Multipair Two-Way Relay Channels

In this paper, we propose a simple yet effective beamforming technique for multiple-input–multiple-output (MIMO) multipair two-way relay channels. Two key ingredients in our technique are adoption of signal space alignment (SSA) for transmit and receive beamforming and amplify-and-forward (AF) relay beamforming using advanced zero-forcing (ZF) technique. From the sum-rate analysis on MIMO multipair two-way relay channels, we show that the proposed method achieves multiplexing gain proportional to the number of user pairs.