Wireless sensor networks typically conserve energy by following a periodic wakeup-sleep schedule: nodes minimize idle time and spend most of their time in a low power sleep state. In order to communicate and exchange data in such a network, the current duty-cycling MAC protocols either require tight synchronization between the neighbor wakeup schedules or spend a significant amount of energy in signaling the sleeping nodes. In contrast, this paper presents Neighborhood-based Power Management (NPM), an energy efficient asynchronous MAC protocol that minimizes signaling overhead through opportunistically gained knowledge about neighbor wakeup schedules. Unlike the synchronization-based MAC protocols, NPM does not require a priori knowledge of the wakeup schedules. Using only a minimal exchange of schedule information, NPM reduces the signaling overhead by shortening the wakeup signal. Furthermore, NPM uses its wakeup signal to awaken all receivers in the neighborhood of the sender, enabling all sender-receiver pairs in that neighborhood to communicate. Our extensive evaluations show that NPM outperforms popular B-MAC [1], X-MAC [2] and SCP [3] protocols under all network conditions. NPM reduces the signaling overhead, with up to 74% savings in energy and 80% reduction in delay.
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