John Heidemann

Ultra-Low Duty Cycle MAC with Scheduled Channel Polling

TitleUltra-Low Duty Cycle MAC with Scheduled Channel Polling
Publication TypeTechnical Report
Year of Publication2005
AuthorsW. Ye, and J. Heidemann
Date Publishedjul

Radio is a major source of energy consumption in sensor networks. MAC protocols such as S-MAC and T-MAC coordinate sleep schedules to reduce energy consumption. Recently, low-power listening (LPL) approaches such as WiseMAC and B-MAC exploit very inexpensive polling of channel activity combined with long preambles before each transmission, reducing energy consumption particularly during low network utilization. Synchronization cost, either explicitly in scheduling, or implicitly in long preambles, limit all these protocols to duty cycles of 1–2%. We demonstrate that \emphultra-low duty cycles of 0.1% and below are possible with a new MAC protocol (SCP-MAC) by optimally combining \emphscheduled communication with \emphchannel polling. This combination prompts three new contributions: First, we establish optimal configurations for both LPL and SCP under fixed conditions, developing a \emphlower bound of energy consumption. We show that scheduling can typically extend lifetime of a network by a factor of 3–6 times over LPL. Second, we demonstrate that SCP works well even when \emphtraffic load varies. While LPL is optimized for known, periodic traffic, long preambles become very costly when traffic varies. In one experiment, SCP reduces energy consumption by a factor of 10 when traffic is bursty. We also show how it can adapt to heavy traffic and stream data in multi-hop networks, reducing latency by 85% and energy by 95% at 9 hops. Finally, we show that SCP can \emphoperate effectively on recent hardware such as 802.15.4 radios. In fact, power consumption of SCP decreases with faster radios, that of LPL-based approaches increases. To our knowledge, SCP is the first MAC that exploits channel polling on this hardware.