An asynchronous scheduled MAC protocol for wireless sensor networks

Wireless sensor networks (WSNs) comprise a number of autonomous sensors and one or more sinks to cooperatively monitor physical or environmental conditions. Energy efficiency is a key design factor of a MAC protocol for WSNs. Due to the importance of the problem, a number of energy efficient MAC protocols have been developed for WSNs. Preamble-sampling based MAC protocols (e.g., B-MAC and X-MAC) have overheads due to their preambles, and are inefficient at large wakeup intervals. SCP-MAC, a synchronous scheduled energy-efficient scheduling MAC protocol, minimizes the preamble by combining preamble sampling and scheduling techniques; however, it does not prevent energy loss due to overhearing; in addition, due to its synchronization procedure, it results in increased contention and delay. In this paper, we present an energy efficient MAC protocol for WSNs that avoids overhearing and reduces contention and delay by asynchronously scheduling the wakeup time of neighboring nodes. We provide an energy consumption analysis for multi-hop networks. To validate our design and analysis, we implement the proposed scheme in TinyOS. Experimental results show that AS-MAC considerably reduces energy consumption, packet loss and delay when compared with existing energy efficient MAC protocols.