A Linear Beamforming Scheme for Multi-user MIMO AF Two-Phase Two-Way Relaying

The technologies of Multiple Input Multiple Output (MIMO) in relay protocols are considered as one of the most promising candidates for next generation wireless communication systems to extend cell coverage and enhance system capacity. However, since a relay station (RS) cannot transmit and receive a signal simultaneously when RS operates in half duplex mode, spectral efficiency of the system is deteriorated. In this paper, we consider multi-user MIMO two-way relay protocol which can improve the spectral efficiency of the relay systems. In our scenario, base station (BS) and mobile stations (MSs) exchange their own messages via RS with two-phase (two time slots), where RS does not have enough number of antennas for decoding the received signal in the time slots of multiple access channel. RS broadcast the received signal and each MS receives the signal includes unknown interferences in this case. To suppress the unknown interferences for MSs, we propose simple and effective beamforming scheme for our multi-user MIMO two-way relaying. We evaluate bit error rate (BER) performance of the proposed beamforming scheme to confirm that the proposed scheme can work well in our two-way relay scenario.