A duty cycle directional MAC protocol for wireless sensor networks The directional transmission and reception of data packets in sensor networks minimize the interference and thereby increase the network throughput, and thus the Directional Sensor Networks (DSN) are getting popularity. However, the use of directional antenna has introduced new problems in designing the medium access control (MAC) protocol in DSNs including the synchonizaiton of antenna direction of a pair of sender-receiver. In this paper, we have developed a duty cycle MAC protocol for DSNs, namely DCD-MAC, that synchronizes each pair of parent-child nodes and schedules their transmissions in such a way that transmission from child nodes minimizes the collision and the nodes are awake only when they have transmission-reception activities. The proposed DCD-MAC is fully distributed and it exploits only localized information to ensure weighted share of the transmission slots among the child nodes. We perform extensive simulations to study the performances of DCD-MAC and the results show that our protocol outperforms a state-of-the-art directional MAC protocol in terms of throughput and network lifetime.