Wireless sensor networks (WSNs) are an important emerging class of embedded distributed systems that consist of low-power devices integrating computation, sensing, and wireless communications. WSNs have been deployed for a wide range of applications, including monitoring microclimates in redwood forests (Tolle et al. 2005), collecting seismic signals from active volcanoes (Werner-Allen et al. 2006), sniper detection in urban settings (Simon et al. 2004), and tracking wildlife (Zhang et al. 2004).
One of the most popular WSN node platforms is the Telos node platform (Polastre et al. 2005a), shown in Figure 5.1. The Telos incorporates a low-power microcontroller (TI MSP430) with 10 KB of SRAM and 48 KB of program ROM; a low-power radio (Chipcon CC2420) that supports the IEEE 802.15.4 standard; and 1 MB of on-board flash memory. Various sensors can be attached to the board; a standard set includes light, temperature, and humidity sensors. An external connector provides digital and analog I/O ports that can be used to mate the node to a wide range of sensors and other devices. The USB connector is used to program the node when plugged into a host, as well as to provide a serial interface. This allows the node to act as a USB wireless transceiver when attached to a base station that collects data from and controls the network.
WSN platforms are designed from the ground up for low-power operation. The Telos consumes approximately 41 mW when the CPU and radio are active, but can drop down to a low-power idle state consuming less than 6 µW.