Duty cycling improves energy efficiency but limits throughput and introduces significant end-to-end delay in wireless sensor networks. In this paper, we present a traffic-adaptive synchronous MAC protocol (TAS-MAC), which is a high throughput low delay MAC protocol tailored for low power consumption. It achieves high throughput by using Time Division Multiple Access (TDMA) with a novel traffic-adaptive allocation mechanism that assigns time slots only to nodes located on active routes. TAS-MAC reduces the end-to-end delay by notifying all nodes on active routes of incoming traffic in advance. These nodes will claim time slots for data transmission and forward a packet through multiple hops in a cycle. The desirable traffic-adaptive feature is achieved by decomposing traffic notification and data transmission scheduling into two phases, specializing their duties and improving their efficiency respectively. Simulation results and tests on TelosB motes demonstrate that the two-phase design significantly improves the throughput of current synchronous MAC protocols and achieves the similar low delay of slot stealing assisted TDMA with much lower power consumption.
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