Abstract: In plain decode-and-forward (DF) cooperative diversity, asymmetric inter-user channel can have an impact on the performance of system and simple signal retransmission for each other is not an efficient diversity manner. In this paper, a new DF cooperative scheme based on signal-space diversity is propesed, in which the retransmission signals of each user always contain its own data frame and are designed in signal space diversity (SSD) manner. So the proposed scheme can defeat the effect of asymmetric inter-user channel and utilize diversity more efficiently. Simulation results prove that the new cooperative scheme achieves better bit error rate performance than both plain DF cooperative and non-cooperation scheme.