Conventional time-division half-duplex relay strategies based on amplify-and-forward or decode-and-forward strategy could relieve relay nodes from full-duplex requirement but lead to degraded spectrum efficiency. Based on the concepts of broadcast channel and multiple access channel

a novel half-duplex relay strategy was proposed

and optimal resource allocation under this strategy was investigated. It is shown that the proposed strategy can improve spectrum efficiency when compared to the conventional amplify-and-forward or decode-and-forward relay strategies.