A Survey on MAC Protocols for Duty-cycled Wireless Sensor Networks

After more than two decades of their introduction, Wireless Sensor Networks (WSNs) remain an active research topic due to their wide range applications in areas such as healthcare, military, monitoring and surveillance systems. In most applications, sensor nodes are constrained in energy supply and communication bandwidth. Therefore, novel techniques to reduce energy inefficiencies and for efficient use of the limited bandwidth resources are essential. Such constraints combined with dense network deployment pose several challenges to the design and management of WSNs and require energy-awareness at all layers of the networking protocol stack. For instance, at the Data-Link layer, low duty cycle Medium Access Control (MAC) protocols trade off latency for energy efficient operation. In this paper, we present a survey of state-of-the-art low duty cycle MAC protocols. We first outline the design challenges for MAC protocols in WSNs. Then, we present a comprehensive survey of the most prominent and recent MAC protocols. These protocols are classified into synchronous and asynchronous based on their mode of operation. Finally, the paper highlight open research problems in MAC layer for WSNs.