29-11-2012, 04:58 PM
PicoRadio Supports Ad Hoc Ultra-Low Power Wireless Networking
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Introduction
Technology advances have made it conceivable
to build and deploy dense wireless networks
of heterogeneous nodes collecting and
disseminating wide ranges of environmental
data. An inspired reader can easily imagine a
multiplicity of scenarios in which these sensor and
actuator networks might excel. The mind-boggling
opportunities emerging from this technology indeed
give rise to new definitions of distributed computing
and user interface.
Crucial to the success of these ubiquitous networks
is the availability of small, lightweight, low-cost network
elements, which we call PicoNodes. These
nodes must be smaller than one cubic centimeter,
weigh less than 100 grams, and cost substantially less
than one dollar. Even more important, the nodes must
use ultra-low power to eliminate frequent battery
replacement. We envision a power-dissipation level
below 100 microwatts, as this would enable selfpowered
nodes using energy extracted from the environment—
an approach called energy-scavenging or
harvesting.1
POWER DISSIPATION TODAY
To put power dissipation into perspective, we can
compare it with the state-of-the-art commercial devices
available today. One of the closest matches is the
Bluetooth transceiver, an emerging standard for shortrange
wireless communications. While meeting the volume
requirement, Bluetooth radios cost more than 10
dollars and consume more than 100 milliwatts.
Although Bluetooth’s price point and power consumption
will inevitably drop with technology scaling,
these modifications would still not address the
orders-of-magnitude reductions required for sensor
network applications.
To reach these aggressive power dissipation levels,
we must limit the effective range of each PicoNode to
a couple of meters at most. Extending the reachable
data range requires a scalable network infrastructure
that allows distant nodes to communicate with each
other. A self-configuring ad hoc networking approach
is key to the deployment of such a network with many
hundreds of nodes.
Reducing the PicoNode’s energy dissipation to this
level is our focus here. The secret lies in a meticulous
concern for energy reduction throughout all layers of
the system design process. The largest opportunity lies
in the protocol stack where a trade-off between communication
and computation, as well as elimination
of overhead, can lead to a many orders-of-magnitude
energy reduction. Other opportunities lie in the adoption
and introduction of novel self-optimizing radio
architectures and opportunities for energy scavenging.
PICORADIO APPLICATIONS
Applications of such sensor and monitoring networks
include environmental control in office buildings;
robot control and guidance in automatic
manufacturing environments; warehouse inventory;
integrated patient monitoring, diagnostics, and drug
administration in hospitals; interactive toys; the smart
home providing security, identification, and personalization;
and interactive museums.
Building control
As one example of an application for PicoRadio networks,
consider the management of environmental control
systems in large office buildings. Any person who
has spent a significant amount of time in such an environment
is acutely aware of its problems: The temperature
or the airflow is never right, and there is too little
or too much light. A distributed building monitor and
control approach might go a long way in addressing
these problems—for example, by creating local microclimates
adapting to an occupant’s preferences through
distributed air ducts—and might vastly improve the living
conditions for the building’s population. At the
same time, such an approach can dramatically reduce
the energy budget needed to manage the environment.
First-order estimations indicate that such technology
could reduce source energy consumption by twoquadrillion
BTUs (British Thermal Units) in the US
alone. This translates to $55 billion per year, and 35
million metric tons of reduced carbon emissions.