Wireless sensor networks

Wireless Sensor Networks are networks
that consists of sensors which are
distributed in an ad hoc manner.
These sensors work with each other to
sense some physical phenomenon and then
the information gathered is processed to get
relevant results.
 A Wireless Sensor Network (WSN)
contain hundreds or thousands of these
sensor nodes.

“A wireless sensor network (WSN)
is a wireless network consisting of
spatially distributed autonomous
devices using sensors to
cooperatively monitor physical or
environmental conditions, such as
temperature, sound, vibration,
pressure, motion or pollutants, at
different locations.”

Wireless sensor networks mainly
use broadcast communication while
ad hoc networks use point-to-point
communication.
Unlike ad hoc networks wireless
sensor networks are limited by
sensors limited power, energy and
computational capability.

Sensor nodes may not have global
ID because of the large amount of
overhead and large number of
sensors.

A Wireless Sensor Network (WSN) contain
hundreds or thousands of sensor nodes.
These sensors have the ability to
communicate either among each other or
directly to an external base-station (BS). A
greater number of sensors allows for
sensing over larger geographical regions
with greater accuracy.

Sensor nodes are usually scattered in a
sensor field, which is an area where the
sensor nodes are deployed. Sensor nodes
coordinate among themselves to produce
high-quality information about the physical
environment. Basically, each sensor node
comprises sensing,processing, transmission,
mobilizer, position finding system, and
power units

A base-station may be a fixed node or a
mobile node capable of connecting the
sensor network to an existing
communications infrastructure or to the
Internet where a user can have access to the
reported data.

Server
Field
Sensor Nodes
Gateway

Gateway : A gateway is an interface
between the application platform and the
wireless nodes on the wireless sensor
network. All information received from the
wireless nodes is aggregated/manipulated
(e.g. translation between network packet
formats) by the gateway and forwarded to
the application. That application may run on
a local computer or a networked computer.

Field: It is the place where all sensor nodes
are deployed.
Sensor/Actuator : This is the device use for
interaction with the physical world to sense
the physical changes.
Server: All the informations taken by the
nodes are received by this server(may be a
computer).

A sensor is a small hardware device
which is capable of generating response
to change in physical environment.
Although sensors are of different type
which are application specific but desired
characteristics of a sensor node are small
size and low power consumption

Microcontroller performs tasks, processes
data and controls the functionality of other
components in the sensor node.
A microcontroller is often the best choice
for embedded systems because of its
flexibility to connect to other devices, ease of
programming, and low power consumption.

The function both
of transmitter and receiver are combined
into a single device know as transceivers are
used in sensor nodes

Flash memories are used due to its cost and
storage capacity.
Two categories of memory based on the
purpose of storage
a) User memory used for storing
application related or personal data.
b) Program memory used for programming
the device.

For the Sensing, Communication and
Data Processing.
Dynamic Power Management (DPM) and
Dynamic Voltage Scaling (DVS)

 There are many reasons why sensor
nodes fail. For example they may fail due
to the lack of energy, due to physical
damage, inactivity, a communication
problem and even environmental
interference.

 The wireless sensor that is remotely
deployed is usually battery operated.
 Thus the life time of the sensor node is
highly dependent on the battery life time.
Alternatively there are times when it is
possible to use a power source close by to
power the node; but this is not always
possible.

The main power drain is through the three
important operations which are sensing,
computation and communication.
Sensing is the capability of the node to
produce a measurable response to change in a
physical condition like temperature or
pressure.
Computation is the task of processing the
data and controlling the other components
in the sensor node.

In addition to which the Sensor node also
communicates with other sensor nodes on the
network via the network that has been
established.
The life time of the wireless sensor is also an
important factor while considering its
efficiency and hence the design of the node is
such that it maximizes the battery life and
reduces the power consumption.

Terrestrial WSNs typically consist of
hundreds to thousands of inexpensive
wireless sensor nodes deployed in a given
area, either in an ad hoc or in a pre-planned
manner. In ad hoc deployment, sensor nodes
can be dropped from a plane and
randomly placed into the target area. In pre-
planned deployment, there is grid placement,
optimal placement, 2-d and 3-d placement
and models.

Underground WSNs and consist of a
number of sensor nodes buried underground
or in a cave or mine used to monitor
underground conditions.

Underwater WSNs consist of a number of
sensor nodes and vehicles deployed
underwater. As opposite to terrestrial
WSNs, underwater sensor nodes are more
expensive and fewer sensor nodes are
deployed. Autonomous underwater
vehicles are used for exploration or
gathering data from sensor nodes.

Multi-Media WSN have been proposed to
enable monitoring and tracking of events in
the form of multi-media such as video,
audio, and imaging. Multi-media WSNs
consist of a number of low cost sensor
nodes equipped with cameras and
microphones.

Mobile WSNs consist of a collection of
sensor nodes that can move on their own
and interact with the physical environment.
Mobile nodes have the ability sense,
compute, and communicate like static
nodes. A key difference is mobile nodes
have the ability to reposition and organize
itself in the network.

Sensor networks can provide variety of
services to military and air force like
information collection, battlefield surveillance,
intrusion detection and attack detection. In
this field of application sensor networks have
quite an advantage over other networks
because enemy attacks can damage or
destroy some of the nodes but nodes failure
in WSN doesn’t affect the whole network.
 Military Applications

Objects moving with significant metallic
content can be detected using specially
designed sensors. So enemies can be tracked
and civilians are ignored. This system
specially helps in detecting armed soldiers
and vehicles.

Critical areas and borders can be closely
monitored using sensor networks to obtain
information about any enemy activity in that
area. This provides quick gathering of
information provides time for quick response.

Sensor networks can be deployed after the
battle or attacks to gather information of
damage assessment.

Sensor networks can be used as Nuclear,
Biological and Chemical warning system. If
any nuclear biological or chemical agents can
be detected by sensors and embedded alert
system can now send a warning message. It
provides the military critical response time to
check the situation and prevent possible
attacks which can save lives of many.

Sensors can be embedded in weapons. Exact
information about the target like distance,
angle can be collected and sent to the
shooter. So sensors can be collaborated with
the weapons for better target assessment.

Millions of sensor nodes can be deployed
which use distributed sensing and collaborate
with each other to provide information. So fire
can be detected and exact location of fire
origin can be provided before the fire is
uncontrollable

ALERT systems use sensors for rain, water
level and weather. Information collected by
these sensors can forecast the possible flood
threats thus providing help for disaster
management.

WSNs can be deployed for monitoring the level of
pollution and warning generation.
Air Pollution Monitoring Systems are deployed in
cities like London and Brisbane to monitor the
level of pollutants.
These sensor networks look for amount of
poisonous gases and these statistics are studied
to analyze if pollution has increased and take
actions to check pollution

 Flexible.
 Implementation cost is cheaper than
wired network.
 Ideal for the non-reachable places such as
across river, or mountain or boarder
areas.
 Ideal for temporary network setups.

 Lower speed compared to wired network.
(of course!)
 Less secure because hacker's laptop can
act as Access Point.
 More complex to configure than wired
network.
 Affected by surrounding. E.g: walls
(blocking), microwave oven
(interference), far distance (attenuation)

 Limited Energy,
 Limited Memory,
 Limited Computing Power,
 Limited Communication Bandwidth,
 Limited Communication Range

 Sensors controlling
appliances and
electrical devices in
the house.
 Better lighting and
heating in office
buildings.
 The Pentagon
building has used
sensors extensively.

 www.slideshare.com
 www.google.com
 www.wikipedia.com
 www.powerstream.com

Prepared by
Aneesh Kumar G
s5 ct

Wireless sensor networks

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