28-12-2012, 02:57 PM
Sensor Networks—Motes, Smart Spaces, and Beyond
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INTRODUCTION
Sensor networks have come a long
way since their humble beginnings
in DARPA-funded academic research
projects in the 1990s and have morphed
into a significant research area in
their own right. Over the last decade
or so, networked sensing devices have
become embedded all around us. In this
article we look at how sensor network
research and applications have evolved
and how emerging trends could determine
where they’re headed.
The Birth of the Mote
Mainstream research in sensor networks
began around the mid-1990s
with a number of DARPA-funded
research initiatives undertaken by top
US universities such as the University
of California, Berkeley. The goal of this
research was to design and create tiny
autonomous computers (called sensor
platforms or in some cases motes) that
could unobtrusively observe their environment
through built-in sensors and
report back to a remote base station.
The primary use cases involved scattering
hundreds or thousands of these
sensor platforms in an area and tasking
them with monitoring vehicular movement
or environmental conditions and
periodically reporting the data.
Berkeley Motes
Berkeley Motes (Figure 1) are probably
one of the best known sensor platforms
in the sensor network research community
primarily due to their early
commercialization by CrossBow Technologies
(www.xbowProducts/
wproductsoverview.aspx).
Commercial versions of the Berkeley
Motes include Rene, Mica, Mica2,
Mica2Dot, MICAz, MICA2dot, Telos
and iMote2. Berkeley Motes were the
result of innovative research spearheaded
by Kristofer Pister and David
Culler at the University of California
Berkeley, that had its roots in the
DARPA Network Embedded Systems
Technology program.
Each mote was essentially made up
of a sensor board with integrated sensors
and a processing board consisting
of a wireless radio transceiver and
a microcontroller. All the motes were
designed to run off standard AA or
Li-ion watch batteries and in optimal
conditions could last more than a year
off a single battery charge. The processing
component typically consisted of an
Atmega128 RISC microcontroller from
Atmel, though more recent versions
(such as Telos and iMote2) used more
powerful microcontrollers such as the
MSP430 from TI and the X-Scale range
from Marvel. The networking hardware
used in different motes consisted
of a number of low-power radios ranging
from the Chipcon CC868 running
proprietary ad-hoc networking stacks
to standardized 802.15.4 radios such as
the Chipcon CC2420, which supported
ZigBee mesh networking stacks.
Smart-Its
The Smart-Its project1 was a collaborative
effort between ETH Zurich,
Lancaster University, the University of
Karlsruhe Interactive Institute and the
Valtion Teknillinen Tutkimuskeskus
(VTT), funded by the European Union’s
Disappearing Computer initiative.
Smart-Its (Figure 2) are sensor platforms
with hardware characteristics
similar to the motes but packaged in
a smaller form factor. The device typically
has two versions, one consisting of
an Atmega103L from Atmel integrated
with an Ericsson Bluetooth radio and
the other featuring a PIC18F252 microcontroller
integrated with a BiM2 or
TR1001 radio transceiver using a proprietary
networking stack.
Phidgets
Saul Greenberg and Chester Fitchett
at the University of Calgary developed
an innovative sensor and actuation
platform called Phidgets or “physical
widgets.”2 Their goal was to package
physical sensors, actuators, and associated
control software into physical widgets
which would provide the same level
of abstraction for physical devices that
software widgets provide to an application
developer. This would enable programmers
to concentrate on developing
end-user applications rather than getting
distracted with low-level hardware
and software issues.
The Phidgets hardware consists of an
interface board with a microcontroller
and USB connectivity that allows developers
to hook up sensors and actuators
(see Figure 3). A PC application can
then access these sensing and actuation
devices through USB. Phidgets provide
intuitive software control libraries for
different sensors and actuators in programming
languages such as Visual
Basic where even novice programmers
can simply drag and drop controls into
their project and quickly create fairly
sophisticated applications with a few
lines of code.
Atlas Platform
The Atlas Platform,3 developed at the
Mobile and Pervasive Computing Laboratory
of the University of Florida,
was one of the first sensor platforms to
utilize Service-Oriented Architecture
(SOA) for automatic self-integration
of sensors and actuators into smart
spaces. Unlike other sensor platforms
which either consisted solely of a set
of distributed sensor nodes (such as
Berkeley Motes) or a set of hardware
adapters driven by PC-based software
(such as Phidgets), Atlas was composed
of semi-autonomous hardware sensor
nodes (see Figure 4) coupled with an
SOA-based backend running on a PC
or server machine.