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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