Sensor networks are an emerging way to monitor inaccessible and unwired places. The units communicate with each other, and send the information they gather at intervals to the human operators. They’re used to monitor wildlife activity, for example.
But sensor network protocols, based on WiFi use too much power. The researchers experimented with Zigbee nodes squeezing out more efficiency and performance.
The protocol is said to combine two techniques: ‘low power listening” in which units switch on for only very brief periods; and “scheduled channel polling” which synchronizes and schedules the listening.
ISI research scientist Wei Ye, working with project leader John Heidemann and programmer Fabio Luis Silva in the ISI Laboratory for Embedded Networked Sensor Experimentation developed the protocol. The research was supported by the National Science Foundation, Intel and other funders.
They implemented SCP-MAC using TinyOS on Mica2 motes from Xbow. Crossbow’s XMesh technology uses low power, 32 bit PXA271 XScale processors with 32MB of RAM and 32 MB of Flash and an integrated 802.15.4 radio with a built-in 2.4GHz antenna.
UCLA’s Center for Embedded Networking Sensing (research projects), “envisions a world where researchers, students, industry and goverment routinely use distributed sensor and actuator networks to understand and control both natural and artificial systems.”
The IEEE 802.15.4 standard operates at data rates of 10 kbps to a max of 250 kbps. Wireless links can operate in three unlicensed frequency bands (2.4GHz, 868Mhz and 915MHz). When lines of communication exceed 30 feet, the 802.15.4 standard creates self-configuring, multihop networks. It is intended to operate in an unlicensed, international frequency band with applications in sensors, interactive toys, smart badges, remote controls, and home automation.
The ZigBee Alliance specification is a combination of HomeRF Lite and the 802.15.4 specification and operates over 16 channels with data transmission rates of up to 250kbps. ZigBee’s technology is slower than 802.11b, Bluetooth and UltraWideBand, but it consumes significantly less power and can connect up to 64,000 nodes on one network.