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Cooperative communication has emerged as a promising technique to enhance system reliability and performances in resource-limited wireless networks. In this paper, we propose a novel cooperative MAC strategy for slow fading Ad hoc networks. Based on cooperative MAC (CMAC) protocol and node cooperative stop and wait (NCSW) ARQ protocol, our node-cooperative retransmission scheme makes three points improvements as follows: 1) In order to avoid ambiguous ACK/NAK and diffusion of cooperation process, cooperative and non-cooperative frames are distinguished. 2) Traffic categories within each node are introduced so that cooperative frames can be sent firstly. 3) According to instantaneous channel conditions, the most appropriate node is selected to help the source node retransmit data. Both the analytical and the simulation results indicate that improved scheme can alleviate collision caused by cooperation and increase the probability of successful retransmissions further.