Joint Signal and Interference Alignment in Two-Way Relay Communications

In this paper, we study the application of physical layer network coding (PNC) and interference alignment scheme to the joint design of uplink and downlink transmissions, where the base station (BS), the mobile stations (MSs) and the relays all have multiple antennas. Leveraging from the interference alignment and physical-layer network coding, a joint signal and interference alignment scheme is proposed, where uplink and downlink communications can be accomplished within two time slots. Since here two relays share the same spectrum to assist the data transmission, co- channel interference (CI) would be induced and the communication reliability would be deteriorated. To address this challenge, precoding matrices at the BS, the MS´s, and relays have been carefully designed to ensure the removal of CI. Additionally, the received signals from BS and MSs are mixed and broadcasted to BS and MSs at the next time duration. Simulation results also demonstrate the performance of the proposed joint signal and interference alignment scheme.