26-06-2013, 03:14 PM
THE PLATFORMS ENABLING WIRELESS SENSOR NETWORKS
ENABLING WIRELESS.pdf (Size: 152.07 KB / Downloads: 20)
INTRODUCTION
Wireless sensor networks combine processing, sensing, and communications into tiny embedded devices. Peer-to-peer communication protocols then combine the individual devices
into an interconnected mesh network where data is seamlessly
routed among all the nodes. These networks require
no external infrastructure and can scale to hundreds
or even thousands of nodes. Here, we explore the standard
sensor network platforms where devices range from millimeter
size custom silicon to PDA-size integrated units. Critical to
the operation of any sensor network device is the ability
to satisfy harsh always-on power requirements.
Unlike cell phones and wireless laptops, periodic
recharging is not possible for most wireless sensor networks.
In many cases, devices are placed in the field
for years at a time without maintenance or human
intervention of any kind.
In sensor networking, special-purpose sensor nodes
are purposely designed to sacrifice flexibility in order
to be as small and inexpensive as possible. Generic
sensor nodes provide a rich expansion interface for
making flexible connections with an array of simple
sensors. High-bandwidth sensor nodes contain the
built-in processing and communication capabilities
needed to deal with complex sensor streams, including
video and voice processing. Gateway nodes provide
a critical link between the sensor network and
traditional networking infrastructures, including Ethernet,
the 802.11 communication standard, and
wide-area networks.
Platform Classes
Initial deployment experience has shown that sensor
network systems require a hierarchy of nodes starting
at low-level sensors and continuing up through
high-level data aggregation, analysis, and storage
nodes (see Figure 1). This tiered architecture is common
in virtually all sensor networks and is best illustrated
by example. Consider a sensor network
for an advanced security system in which a majority of
the sensors cover window breakage, contact closure,
and motion detection. The quantity and range of
locations for these simple sensors require that they be
battery powered. They are complemented by a handful
of more advanced sensors, including cameras and
acoustic and chemical detectors, placed in key locations.
Both simple and complex sensor data is routed
over a mesh network into a building-monitoring-andcontrol
facility that provides a continuious monitoring
capability.
Platform Road Map
The recent research and development
of first-generation wireless
sensor network platforms is now
feeding back on itself to help systems
engineers define a new generation
of hardware better able to
meet network demands. Table 2
outlines the sensor network hardware
platforms available today.
Hardware progression. Analyzing
the progression of sensor-network
hardware must account for the
influence of Moore’s Law on the
design and development of the
networks. For all platform classes
except special-purpose sensor
nodes, Moore’s Law promises an
increase in performance for a given
power budget.
Conclusion
The age of ubiquitous sensing and actuation is being
fueled by Moore’s Law and the development of
advanced wireless sensor-networking platforms.
Hardware can be used to deploy data-collection networks
capable of operating for years without maintenance
in remote, often hostile, environments. As
capabilities improve, these systems will thus be able
to automatically act on sensor data to manage our
environment for us.
Most current sensor-networking deployments
include square-inch-size generic sensor devices that
represent an interconnected mesh tied to the Internet
through one or more gateway-class devices. More
advanced networks include high-bandwidth sensor
nodes capable of dealing with complex data streams,
including voice and video. Alternatively, they may
include tiny special-purpose sensor nodes that are just
millimeters on a side and weigh only a few grams
each. While the capabilities, cost, and size of each
class of device will change with technological
advances, these four fundamental classes of device will
likely remain for the foreseeable future.