Efficient Asynchronous Low Power Listening for Wireless Sensor Networks

Abstract

Energy conservation and reliability of wireless communications are two crucial requirements of practical sensor networks. Radio duty cycling is a widely used mechanism to reduce energy consumption of sensor devices and to increase the lifetime of the network. A side effect of radio duty cycling is that it can cause the wireless communications to be unreliable---if a sender node transmits a packet while the receiver is asleep, the communication fails. Early duty cycling protocols like B-MAC that were designed for bit streaming radios achieve low duty cycle by keeping the radio transceiver awake for short time periods. However, they require a transmitter node to precede a packet transmission with a long preamble to ensure the reliability of wireless communication. Furthermore, they cannot be used with modern packet radios like widely used IEEE 802.15.4 based radio transceivers, which cannot transmit arbitrarily long preambles. Recent duty cycling schemes like X-MAC, on the other hand, reduce the length of the preamble and are designed to work with packet radios. However, in order to ensure that a receiver can reliably detect a transmitter's preamble transmission, these schemes need to turn the radio transceiver on for longer time durations than the early schemes like B-MAC. In this paper, we present a novel duty cycling scheme called Quick MAC, that achieves a very low duty cycle without compromising the reliability of wireless communication. Furthermore, Quick MAC is stateless, compatible with packet (and bit stream) radios, and does not require synchronization among sensor nodes. From our experiments using TMote sky motes, we show that Quick MAC reduces duty cycle by a factor of about 4 compared to X-MAC, and yet maintains the same level of reliability of wireless communication as X-MAC.