John Heidemann

Energy and Latency Control in Low Duty Cycle MAC Protocols

TitleEnergy and Latency Control in Low Duty Cycle MAC Protocols
Publication TypeTechnical Report
Year of Publication2004
AuthorsY. Li, W. Ye, and J. Heidemann
Date Publishedsep

Recently, several MAC protocols such as S-MAC and T-MAC have exploited scheduled sleep/wakeup cycles to conserve energy in sensor networks. Until now, most protocols have assumed all nodes in the network were configured to follow the same schedule, or they assumed border nodes would follow multiple schedules, but did not evaluate those cases. This paper develops two new algorithms to control and exploit the presence of multiple schedules to reduce energy consumption and latency. The first one is the \emphglobal schedule algorithm (GSA). Through experiments, we demonstrate that, because of radio propagation vagaries, large sensor networks have very ragged, overlapping borders where many nodes listen to two or more schedules. GSA is a fully distributed algorithm that allows a large network to converge on a single global schedule to conserve energy. Secondly, we demonstrate that strict schedules incur a latency penalty in a multi-hop network when packets must wait for the next schedule for transmission. To reduce latency in multi-hop paths we develop the \emphfast path algorithm (FPA). FPA provides fast data forwarding paths by adding additional wake-up periods on the nodes along paths from sources to sinks. We evaluate both algorithms through experiments on Berkeley motes and demonstrate that the protocols accomplish their goals of reducing energy consumption and latency in large sensor networks.