QoS-driven robust beamforming and power allocation in rateless network coded two-way relaying systems

In this paper, we consider a two-way relaying system where two source nodes communicate with the aid of a multiantenna relay. In order to improve spectrum efficiency and enhance transmission reliability simultaneously, a transmission scheme of network coding combining with rateless coding is designed for this relaying system. Distinct from traditional amplifying-forward (AF) and decoding-forward (DF) relaying schemes, our proposed scheme just applies a soft decision to the mixed signal at the relay, leading to a low computation complexity. Moreover, to satisfy the quality of service (QoS) requirements of both source nodes with minimal power, a beamforming design method is proposed by effectively exploiting the spatial degree of freedom at the multiantenna relay. Furthermore, considering the imperfect channel state information (CSI) in practical systems, a robust beamforming design method is presented accordingly. Finally, simulation results validate the effectiveness of our theoretical claims.