A three-way relaying system with QoS constraints

A three-way relaying scheme is proposed, in which three single antenna users communicate with each other with the help of an amplify-and-forward relay equipped with multiple antennas. The communication is implemented in two slots. In the first slot the nodes transmit simultaneously, and in the second slot, the relay beamforms the signals received by its antennas. Two relaying strategies are proposed. In the first one, the relay is responsible of interference cancelation (IC) at the destinations via an appropriately designed beamforming matrix. In the second one, the destinations as well as the relay are responsible for IC. While the former strategy requires three antennas on the relay, it is shown that the latter strategy requires only two antennas. Power allocation for both cases is determined so that the transmit power of the users is minimized while individual users´ QoS requirements and the relay power constraint are met. Assuming that the users transmit simultaneously and have distinct destinations, a throughput of 1.5 packets per slot can be achieved. A user packet buffering scheme is proposed to guarantee the above throughput even in cases where the destinations are not distinct.