ELECTION: Energy-efficient and Low-latEncy sCheduling Technique for wIreless sensOr Networks ∗ Shamim Begum, Shao-Cheng Wang, Bhaskar Krishnamachari, Ahmed Helmy Email: {sbegum, shaochew, bkrishna, helmy}@usc.edu Department of Electrical Engineering-Systems University of Southern California Abstract We propose ELECTION, a new sleep scheduling scheme that adaptively schedules the sleep cycles of both com- munication radios and sensors in wireless active sen- sor networks. Taking advantage of spatial and tempo- ral correlations in the underlying physical phenomenon, our scheme controls sleeping schedules of radios and sensors, and adaptively meets the energy efficiency, la- tency and responsiveness needs of applications. During the normal phase of operation, sensors take samples of the environment once at each wakeup time, and based on the perceived environment they adapt their sleep cy- cles. When an abnormality is perceived from the sam- pled data, sensors communicate with their neighbors to form a cluster and report to the base station. Analysis and simulation results show that ELECTION outper- forms existing protocols significantly in terms of energy savings as well as delay and responsiveness. 1 Introduction Recent advances in microelectronics, integrated circuits and communications have allowed sensor integration with processing and communicating capabilities into low-cost embedded sensor devices. These devices are capable of monitoring a wide variety of ambient con- ditions: temperature, pressure, humidity, soil makeup, vehicular movement, noise levels, lighting conditions, the presence or absence of certain kinds of objects [1]. These devices are empowered with certain processing, memory, and communication capabilities. Networking such devices serve a wide varieties of applications rang- ing from environmental [2], structural [3], factory, and seismic [4] monitoring to target tracking. Each of these deployments involve a large number of sensor devices and is expected to last as long as possible. In past few years achieving energy efficiency for these wireless sensor networks (WSN) has been the most im- * This work is supported in part by NSF grants 0325875, and 0347621. portant research challenge. Energy efficient protocols have been proposed for MAC [5, 6, 7], topology control [8, 9, 12], and data aggregation [16, 17]. The main fo- cus of these works is in the design of novel sleep schedul- ing schemes wherein nodes turn off their communication radios during the sleep. Typically these works assume passive sensors where sensor themselves consume very insignificant amount of power. In contrast, we present a new sleep scheduling scheme that schedules both communication radios and the sen- sors. We assume smart (or active) sensors where sen- sors act as smart agents, and are able to sense the en- vironment in a responsive and timely manner. They communicate to each other using communication radios to perform collaborative and integrated sensing. These sensors are massively deployed in an environment and configured in a network to communicate to a base sta- tion to report the accumulated data. The sensor pod developed by NASA’s Jet Propulsion Laboratories is an example of smart sensor [18]. These sensors can be used in similar deployments for environmental and structural monitoring to monitor physical phenomenons. When the processor and communication radios are off, these sensors consume about 20% energy of transmission, and therefore controlling these sensors has been a source of significant energy savings compared to traditional pas- sive systems [19]. We take an example of a wireless network of active sensors deployed to monitor some phenomenon in a chemical powerplant. The network is monitoring the en- vironment to report any abnormalities of the underlying phenomenon. Energy efficiency, delay and responsive- ness of such applications vary with different modes or phases of the applications. For example, during normal operation, achieving energy-efficiency is more important than assuring low latency or high responsiveness. While the phenomenon tends to increase because of some ab- normalities in the environment, it is more important to ensure low latency and high responsiveness than energy- efficiency. Designing a sleep scheduling scheme that ad- 1 Proceedings of the 29th Annual IEEE International Conference on Local Computer Networks (LCN’04) 0742-1303/04 $ 20.00 IEEE Authorized licensed use limited to: University of Maryland College Park. Downloaded on October 25, 2009 at 21:20 from IEEE Xplore. Restrictions apply.