A Sensor Network is a communications infrastructure
that employs a network of distributed sensors and sensor nodes
to acquire data and relay it to a central monitoring location.
Advanced networks often employ ad hoc mesh networking
that allows sensor nodes to self-configure. When sensors are attached
to hardware with advanced, embedded data processing abilities,
the entire assembly is referred to as a Smart Sensor Node. Depending
upon the desired application, a sensor network may be wired, wireless
or a combination of both, depending on the need of the application
and the environment where it is deployed. Sensor networks are
frequently used to create smart environments that
allow for the monitoring and control of everything from in home
lighting to structural health monitoring to covert security monitoring.
A sensor network is generally
composed of two primary networks:
Data Acquisition Network: smart sensor
nodes collect data, process data and deliver it to base stations
(or other gateway devices), where various stages of data processing
occur. Ultimately, the data is transmitted to a management center
for storage, analysis and further processing.
Data Distribution Network Information
may be transmitted to a variety of devices including laptops,
PCs, PDAs, cell phones and internet cloud servers.
If the network is designed accordingly, sensors may be remotely
controlled, allowing for re-calibration and measurement updates.
Functions Employed in a
Smart Sensor Nodes: Collects measured
data from one or more sensors. Processes, stores and transmits
data. Receives incoming messages and commands.
Sensor Control Module (SCM): Aggregates
and synchronizes sensor data from multiple nodes. Performs processing,
stores, and transmits data.
Base Control Modules (BCM): Forwards
the information provided by the sensor control module to a server.
Also allows for some further processing and filtering of sensor
data; as well as additional routing functions.
Embedded Processing: Distributed at multiple
levels throughout the sensor network modules.
Power Management Control Module: Manages
the overall energy efficiency of a sensor network: may include
standard hard-wired or battery power, as well as energy harvested
power generation options.
Multi Sensor Data Fusion (MSDF): Provides
the ability to fuse data from a variety of sensors, as well as
fuse multiple sets of data together using a time stamp to sequence/synchronize.
The standard digital tool for combining the information from many
sensors is the Kalman Filter.
Application Software: Allows the
end user statically analyze, manipulate and visualize the sensor
data, as well as remotely control the network.
Function Employed in a Sensor
Sensor Types and Technologies:
The basis for all sensor measurements is the
transduction principle - this requires that the physical property
being measured can be distinguished from the background noise
and translated into a usable signal. Good quality sensors are
manufactured so that the physical change being measured is extremely
predictable over the desired range. Sensor manufacturing techniques
employ specialized materials ranging from piezoelectric and photoconductive
solar cells, to MEMS silicon etched micro-devices and thin-film
coated biochemical materials.
Wind Speed and Direction
Relative and Absolute Position
Strain, Force, Torque
direct physical contact
not require direct physical contact
temperature & heat gradients
photons (IR, Visible and UV) into a detectible signal
Cells, Fiber Optics
with solids, liquids, gases
MEMS (Microelectromechanical systems):
MEMS are silicon semiconductor based microdevices
and range in size from 0.02 to 1.0 mm. Microsensors have been
designed that mimic all types of larger scale sensor technologies.
MEMS sensors often have built in signal conditioning and temperature
compensation to boost the signal-to-noise ratio and provide an
accurate sensor measurement.
Network Communications Topologies:
Communications topology refers to the
manner in which a networks nodes are connected, in order
to transmit, receive and route messages. The topology is determined
by the communication requirements, and constraints of a given
network. Several different topologies (subnets) may be combined
within a single sensor network. Examples include: Mesh networking,
star, bus, ring and tree, etc.
Sensor Network Architecture:
The architecture of a sensor network may be
organized into layers that control various functions. The ISO,
open standard OSI/RM, is based on the use of seven architectural
layers, as follows: Physical, Link, Network, Transport, Session,
Presentation and Application. For example, the lowest layer (physical
layer) controls the transmission device, while the next layer
(Link Layer) determines when the channel is clear for transmission.
Many of the IEEE networking standards support this layered architecture
To ensure maximal network connectivity, various
routing schemes, and self-healing algorithms, are employed to
tackle the issues of blocked connections and data recovery. Examples
include: adaptive routing and multi-hop
Sensor Network Standards
Many different standards and protocols have
been developed to encourage standardization within the Sensor
Network Industry. A few of the most common standards are:
IEEE 1451 (Standard for Smart Sensor Network)
IEEE 802.15.4 (ZigBee)
IEEE 802.11 (WiFi)
IEEE 802.15 (Bluetooth)
Mobile Sensor Networks
Mobile networks are specialized types of wireless
sensor network (WSN) that lend locomotion and GPS tracking to
sensor nodes and other network components to expand the application
abilities of a sensor network.