Process-and-Forward two-way relay using multiple space-time line codes

Abstract

In this paper, we consider a two-way relay (TWR) network that two source nodes (SNs) with multiple antennas exchange data to each other via a relay node (RN) with multiple antennas, when full channel state information (CSI) is available at RN and no CSIs are available at SNs. In case that both SNs transmit space-time block coded multiple data streams to the RN, a new precoding method is proposed for the RN by combing block-wise processing and multiple space-time line codes (STLCs) requiring no CSI at the receiver except the channel norm. An optimal precoding matrix is derived that maximized the minimum achievable rate using a gradient-based iterative algorithm. Moreover, to reduce the design complexity, we derive the closed-form precoding matrix minimizing the total mean square error (MSE), and its theoretical performance is analyzed in terms of the per-stream MSE and detection signal-to-interference-plus-noise ratio. Through numerical simulations, the theoretical MSE is verified by comparing with an experimental MSE, and it is demonstrated that the proposed precoding method is more beneficial than existing retransmission methods for the RN when the SN transfers both single and multiple data stream(s).