Pervasive Wireless Networks
The future of computing aims to bring compelling applications for wirelessly-enabled handheld devices such as cell phones and Personal Digital Assistants (PDAs). In fact, researchers estimate that annual sales of handheld devices will pass 20 million. Unlike desktop computers, today's mobile devices are designed with minimizing power consumption in mind. This need to conserve power has influenced a number of design and manufacturing decisions making these devices perhaps more energy efficient.

Yet, while these devices demand less power than a computer, their consumption certainly is not insignificant. Devices such as cell phones often stay on 24 hours a day. Further, many wireless technologies work by broadcasting messages at a certain frequency in all directions instead of only sending information down a single network wire like a traditional computer network. Further, wireless stations are left always on listening for messages from the wireless devices. The base stations for cellphones require around a few kilowatts per hour leading to significant energy usage.

Crickets
The MIT Laboratory for Computer Science has developed their own wireless device, a core component of Project Oxygen, their vision of future computing. Global Positioning System (GPS), well known for its ability to determine its location, is particularly ill-suited for indoor environments. The MIT LCS Crickets address this problem using RF and ultrasonic signals to provide location detection. The Cricket system consist of a Beacon and Listener. The Beacon is generally spread throughout a building, mounted on walls and transmits concurrent ultrasonic pulses (Left Image).

The Listeners can connect to devices through an RS232 connection and listen for RF signals from the Beacons (Right Image).

With this location technology a host of compelling context-aware applications can be developed. However, this system requires that Beacons are constantly on even when listeners are not present. In fact, both Cricket Beacons and Listeners use considerable energy use. Fortunately, LCS uses rechargeable batteries for their Cricket System.

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