Coop-DMAC: A Cooperative Directional MAC protocol for wireless networks Directional antennas in wireless networks can provide substantial performance gain and opportunities. In the case of high-frequency systems, such as emerging 60 GHz networks, they are inherent feature of the system design. In contrast to the traditional omni-directional antennas, directional antennas are capable of reducing the interference level, increasing the communication range, and improving spatial reuse. However, new challenges need to be solved, such as the deafness problem and the asymmetric-in-gain. In this paper, we propose Cooperative-Directional MAC (Coop-DMAC) protocol to address the new challenges. The Coop-DMAC is completely distributed and relies on limited cooperation between networked nodes. In Coop-DMAC, nodes are supposed to exchange local information including the angle of arrival of their neighboring nodes and the duration of data transmission to improve their spatial reuse. In this paper, we analyze and evaluate the performance of Coop-DMAC, and pay particular attention to the performance and network topology. Simulation results validate our theoretical analysis and show that the proposed Coop-DMAC protocol outperforms the standard IEEE 802.11ad MAC protocol in terms of higher goodput in most common network topologies considered in the paper.