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Cooperative communications achieve tremendous improvements in system performance. Meanwhile, it tends to change the conventional access and transmission schemes in wireless networks. Thus, CoopMAC is proposed and analyzed for fully connected WLANs. It improves the performance of the network dramatically by enabling additional collaboration from other nodes. However, how does it work in multi-hop Ad Hoc networks is not well-understood yet. In this paper, we first propose an analytical model to evaluate the performance of CoopMAC for multi-hop Ad Hoc networks with consideration of hidden node problem. Our analysis results show that the cooperative transmissions are frequently interrupted by hidden nodes' interference. To mitigate the effect of hidden node, an enhanced CoopMAC (ECoopMAC) is further proposed without introducing any overhead and complexity, which jointly optimizes the order of handshake and the helper selection metric. By increasing the probability of successful cooperative transmission and decreasing the interference to other flows, the saturated throughput and access delay of multi-hop Ad Hoc networks are improved by ECoopMAC remarkably. Extensive simulations evaluate the performance of our analytical model and protocol, the results of analysis and simulation match well. Compared with CoopMAC, the saturated throughput is improved up to 12% on average.