wireless sensor networks
TRANSCRIPT
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Wireless Sensor Networks
Technology Overview
The individual nodes that constitute a wireless sensor network are generally small
in size and use power-efficient batteries to extend their operational longevity. Depending
on its function, each node has a sensor board that facilitates the detection and
measurement of heat, vibrations, air-pressure and magnetic fields (among other things).
The “motes” developed at UC Berkeley are a typical example of such devices. Motes
have a range of about 100 feet and feature a 7Mhz processor, 4Kb of RAM, 128Kb of
programmable memory space, and utilize a ChipCon CC1000 radio for communication.
Due to their deployment simplicity and low cost of about $200 per unit, motes can be
distributed in spatially dense configurations within a given area. Motes make use of Tiny
OS, an operating system designed from scratch to be as power-efficient as possible.
Using less than half the capacity of an AA battery, Tiny OS can effectively run
applications for months at a time. (Hellerstein, Hong, Madden, 2003)
Motes within a given geographic location use networking software to self-
assemble into ad-hoc networks, allowing data to be transferred to and from any node in
its network, or if necessary, to a proxy (but unauthorized, non-peer/client) in close
proximity (like a random cell-phone or laptop), thereby serving as a conduit to a wider
network (like the internet).
The nodes in wireless sensor networks can be employed to capture data about
their geographic environment while seamlessly and instantly communicating that
information with surrounding nodes, impervious to temporal or spatial limitation.
Wireless sensor networks circumvent the hindrances of collecting information from
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geographic locations otherwise inaccessible by human beings; from the nether ocean to
enemy occupied territory. (Kumar, 2003)
Sensor networks are amenable to both civilian and military deployment. In
civilian scenarios, sensors used to monitor traffic, pollution, or infrastructure can be
positioned by hand. In terms of the most basic military applications, such networks can
be used to detect, classify, and track targets in a given territory (other applications will be
discussed later). Civilian use of wireless sensor networks range from environmental
purposes such as pollution and ecosystem analysis to law-enforcement activity like traffic
monitoring and criminal surveillance. In their military context, discommodious or threat-
rich environments can be accurately and safely reconnoitered, determining sensor
placement a priori is unnecessary as random and widespread sensor deployment can be
achieved via aircraft. (Clouqueur, Veradej, Ramanathan, Saluja, 2003)
Development Status
Sensor technology has made substantial advancements thanks to innovative new
research efforts. Some recent developments have been academic in nature, like tracking
and monitoring animal migrations, bird habitats, or vineyards, while private-sector
developments have included efficiency improvements like “condition-based” equipment
maintenance. There are numerous examples of how wireless sensor networks are
currently being used, for instance, biologists at UC Berkeley interested in studying how
trees affect the temperature and humidity in their surrounding canopy use a network of
trunk-attached motes to monitor the microclimates around the redwood trees in their
botanical garden. (Hellerstein, Hong, Madden, 2003)
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One of the most promising research endeavors currently underway is the
development of a flexible and interference-resistant communication technology. Instead
of being restricted to transmitting and receiving information on a pre-assigned block of
spectrum, these radio devices would utilize “opportunistic spectrum access”. Such
systems would facilitate faster and more efficient communication since static allotment
would be complemented by instantaneous and opportunistic spectrum access. Sensor
nodes utilizing such technology would access unused spectrum, detect, authorize and
network surrounding nodes in a manner that reduces inter-node communication
interference. (DARPA “neXt Generation” program)
A second area of research worthy of mentioning employs “mobile swarm” sensor
networks to facilitate asset management and multimedia streaming. Mobile swarms are
clusters of sensor nodes located in close physical proximity to each other and possess
similar mobility patterns. For example, a group of tanks or UAVs could constitute a
swarm, presumably equipped with qualitatively superior sensors like hi-res cameras, and
longer range radios with higher channel bandwidths than conventional motes. Sensor
nodes attached to the swarm members can gather information about that individual
member, like location or operating status, but it can also relay data captured by its “host”
to other nodes in the swarm, other mobile swarms, or to a command center through a
backbone network or satellite. (Gerla, Xu)
There are three primary motivations supporting research and development in the
field of wireless sensor networks: academic interest, corporate profit, civil value, and of
course, military application. These strong and mutually supportive driving forces suggest
a promising future for the technology. Although motes currently cost about $200 per unit,
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prices have been dropping steadily and are expected to continue falling. Some projections
suggest that the price will fall to around $10 a piece within the next few years and that the
units themselves will shrink in size to about 2 cubic mm. It is safe to assume that the
smaller and cheaper these sensors get, the more widely used they will become. Moore’s
law indicates that in about ten years, devices as small as a mote will have processing and
memory capabilities similar to a contemporary network server. (Hellerstein, Hong,
Madden, 2003)
Several challenges faced by sensor technology are worthy of closer scrutiny.
Software development, for instance, has been particularly troublesome. This is primarily
due to the sensor’s hardware limitations. Modern sensors like motes suffer from a dearth
in processing speed, memory, radio bandwidth, and energy capacity. The problems with
processing speed and memory are likely to be resolved in the near future. However, the
shortage in bandwidth is due to insufficient energy, and because the energy density of
commercial batteries has not changed much in the last ten years, it is unlikely that the
challenges posed by battery capacity and radio bandwidth will be overcome anytime
soon. Other problems involve developing a way of programming groups of sensors to
undertake a variety of different tasks and creating reliable security protocols to ensure
network integrity and guard against intrusion and denial-of-service threats. (Hellerstein,
Hong, Madden, 2003)
Although most challenges are developmental, the technology’s inherent potential
to violate widely held standards of personal privacy implies that there are also social and
legal obstacles to many of its civil applications. Critics are quick to point out the ways
such technology can be misused, from tracking ones every movement to remotely
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accessing personal information. It is not difficult to imagine scenarios whereby one need
merely walk by the wrong person in a grocery store to share one’s home address, credit
card number, or other identity information. These are valid concerns that warrant
significant discussion and policy-formulation prior to any civil application.
Security Implications
In contrast to civilian applications, the military applications of wireless sensor
networks must be fully understood, embraced, and implemented without delay. Until
now, the United States’ military use of sensor technology has been limited to basic and
relatively crude detectors that utilize sensor technology, the Unattended Ground Sensor
(UGS) system and the AN/GSQ-187 Remote Battlefield Sensor System (REMBASS) are
typical examples of such devices. Although technically “wireless” by definition (in the
sense that they do not require external cables to function), these devices do not utilize the
technology discussed in this report, nor do they form ad-hoc networks of any kind. These
systems are capable of detecting vehicle and personnel activity, but would be incapable
of providing potentially critical battlefield information in the form of real-time
audio/video data.
Wireless sensor networks can also provide a strategic advantage in urban and
close-quarter combat situations. For instance, an orbiting UAV could automatically detect
friendly forces in the area and transmit aerial reconnaissance data directly to a heads-up
display build into the helmets of troops on the ground. If a ground unit required a
topographical map of an area, it could transmit the request to a nearby tank or UAV
which would then acquire the information from a satellite or databank at a command
center.
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Military integration of this technology will require simultaneous training and
tactical adaptation. The ability of its operators to function effectively in an information-
rich environment will ultimately depend on the quality of their training. US combat
statistics from the first Gulf War indicate that an abundance of battlefield information
actually degrades combat performance. Its recipients could not process all the
information at every level of command so units in critical need of information had to sift
through too much irrelevant data to locate the specific details they required. The
confusion caused by information overload illustrates the importance of implementing
training and tactical reform measures whenever new technology is introduced. (Davis,
2007)
It should be noted that military use of wireless sensor networks need not be
limited to information awareness purposes. While not the most creative of individuals, I
can think of a few applications omitted from existing literature on the subject. First,
integrating wireless sensor networking technology with anti-tank, anti-ship, or anti-
personnel mines could facilitate a strategic self-repositioning function. Should an existing
mine be detonated, the remaining mines/nodes in the network would detect the
detonation’s location and adjust themselves accordingly, either filling in any gaps in the
mine field or congregating in the area of activity. Another application might involve
attaching wireless sensor nodes to handheld weapons. Potential benefits could include
user-authentication, battlefield restriction (they become unusable when taken out of an
AO), or perhaps “talking” with other weapons in the unit and automatically
communicating the need for reinforcements or ammunition re-supply based on usage or
environment data.
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Regardless of application, wireless sensor networks portend significant defense
and security implications, necessitating a response in the form of policy formulation. Any
military seeking to become or remain a formidable force should carefully consider the
strategic opportunities wireless sensor networking technology can provide. Given the cost
of military conflict, in terms of both monetary expense and potential casualties, a prudent
strategist must pay close attention to technologies that could result in an advantage of any
sort. Military history suggests that success is not achieved by those who first acquire a
new technology, but by those who accept it and learn to wield it effectively.
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References
T. Clouqueur, P. Veradej, P. Ramanathan, K. Saluja, “Sensor Deployment Strategy for
Detection of Targets Traversing a Region,” Mobile Networks and Applications,
2003.
D. Davis “Synthetic Battlespace Test-bed for the Analysis of New Intelligence Sensors,
Platforms and Techniques: A National Intelligence Simulation Center,”
University of Southern California, 2007.
M. Gerla, K. Xu, “Multimedia Streaming in Large-Scale Sensor Networks with Mobile
Swarms,” UCLA Computer Science Department.
J. Hellerstein, W. Hong, S. Madden, “The Sensor Spectrum: Technology, Trends, and
Requirements,” SIGMOD Record, December 2003.
V. Kumar, “Sensor: The Atomic Computing Particle,” SIGMOD Record, December
2003.
XG Working Group, “The XG Vision: Request for Comments,” DARPA, Version 2.0