Joint link-and-user scheduling for buffer-aided relaying system with adaptive rate transmission

In this paper, we consider a relaying system which consists of a multiple-antenna source node (SN), M single-antenna destination nodes (DNs) and a multiple-antenna relay node (RN). The RN possesses a buffer and it is able to store the decoded message before retransmitting the message to the DNs. We use the joint link-and-user scheduling method to maximize the long term average achievable rate of a multiple-input multiple-output (MIMO) relaying system. The optimal scheduling criteria is obtained and a two-step approach is proposed to implement it. In addition, we propose a rate allocation scheme of the source-relay (S-R) link to preserve the flow conservation constraint of each individual user. Furthermore, two reduced complexity joint link-and-user scheduling methods which use the zero forcing (ZF) beamforming in the relay-destination (RD) link are investigated. It is shown that joint link-and-user scheduling can significantly increase the average achievable rate of the system.