Practical Lazy Scheduling in Wireless Sensor Networks

Experience has shown that the power consumption of sensors and other wireless computational devices is often dominated by their communication patterns. We present a practical realization of lazy packet scheduling that attempts to minimize the total transmission energy in a broadcast network by dynamically adjusting each node’s transmission power and rate on a per-packet basis. Lazy packet scheduling leverages the fact that many channel coding schemes are more efficient at lower transmission rates; that is, the energy required to send a fixed amount of data can be reduced by transmitting the data at a lower bit rate and transmission power. The optimal per-packet transmission rate in a multi-node network is governed in practice by the available bit rates of the given transceiver(s), the nodes’ delay tolerance, and the offered load at every node contending for the shared broadcast channel. We propose an extension to the traditional CSMA/CA MAC scheme called L-CSMA/CA that allows individual nodes to continually estimate the current demand for a broadcast channel and adjust their transmission schedules accordingly. Our simulation results show that L-CSMA/CA can provide improved energy efficiency in a singlehop, broadcast network (20–25% with more than 10 nodes, and up to 99% for four nodes with a standard power function) for both Poisson and bursty arrivals with only minor degradation the capacity of the channel.