Pair-aware transceive beamforming for non-regenerative multi-user two-way relaying

In non-regenerative two-way relaying, two communicating nodes transmit simultaneously to the Relay Station (RS). The RS processes the received signal and forwards it to both nodes simultaneously. In order to obtain its partner´s information, each node performs self-interference cancellation by subtracting its transmitted signal from its received signal. However, in multi-user two-way relaying, the interference at each node is not only the a priori self-interference, but also the interference from the other two-way pairs´ nodes. Using Zero Forcing (ZF) transceive beamforming, the RS spends unnecessary energy to cancel the interference that can be cancelled by the nodes. Therefore, we propose to apply pair-aware transceive beamforming (PATB) at the RS to cancel only the other-pair interference and let each node cancels its self-interference. Two PATB schemes are proposed, namely, pair-aware (PA) matched filter (PA-MF) and PA semidefinite relaxation of maximising the minimum signal to noise ratio (PA-SDR). From sum rate analysis, PA-SDR outperforms PA-MF, and both outperform non-PA ZF.