Download WIRELESS SENSOR NETWORKS

WIRELESS SENSOR
NETWORKS
BY
VENKAT KANCHERLA
VIJAY CHAND UYYURU
Introduction




A sensor network consists of a large number densely
populated sensors acting as nodes in the network.
A sensor network is composed of a large number of
sensor nodes, which are densely deployed either inside the
phenomenon or very close to it.
Sensor data is shared between the sensors and used as
input to a distributed estimation system which aims to
extract as much relevant information from the available
sensor data
The fundamental objectives for sensor networks are
reliability, accuracy, flexibility, cost effectiveness and
ease of deployment.
Introduction (contd…)


A sensor network is made up of individual
multifunctional sensor nodes
The sensor node itself may be composed of various
elements such as various multi-mode sensing hardware
(acoustic, seismic, infrared, magnetic, chemical, imagers,
microradars), embedded processor, memory, powersupply, communications device (wireless and/or wired)
and location determination capabilities (through local
or global techniques).
Wireless sensor network device
designed to be the approximate size of a quarter.
Adhoc networks




Ad hoc networks are a new paradigm of wireless communication for
mobile hosts (which we call nodes).
In an ad hoc network, there is no fixed infrastructure such as base
stations or mobile switching centers.
Mobile nodes that are within each other’s radio range communicate
directly via wireless links, while those that are far apart rely on other
nodes to relay messages as routers. Node mobility in an ad hoc
network causes frequent changes of the network topology.
Figure 1 shows such an example: initially, nodes A and D have a
direct link between them. When D moves out of A’s radio range, the
link is broken. However, the network is still connected, because A can
reach D through C, E, and F.
Figure1
Sensor networks VS ad hoc networks:







The number of nodes in a sensor network can be several orders
of magnitude higher than the nodes in an ad hoc network.
Sensor nodes are densely deployed.
Sensor nodes are prone to failures.
The topology of a sensor network changes very frequently
Sensor nodes mainly use broadcast, most ad hoc networks are
based on p2p.
Sensor nodes are limited in power, computational capacities and
memory.
Sensor nodes may not have global ID.
Wireless sensor have many
application areas including
Military,
 Environmental,
 Health,
 Home,
 Disaster relief,
 Space exploration,
 Chemical processing,
 Other commercial

Military Applications







An integrated part of C4ISRT (command, control, communications,
computer, surveillance, reconnaissance, targeting) systems:
Enhanced logistics systems to monitor friendly forces, equipment
and ammunition.
Enhanced surveillance systems to detect intruders, chemical or
biological attacks, underwater targets, firing guns and their locations.
Enhanced reconnaissance systems that can run in inaccessible or
contaminated terrains and beyond the enemy lines.
Enhanced targeting and target tracking systems.
Battle damage assessment systems.
Enhanced guidance and navigation systems.
Civilian Applications:









Habitat monitoring.
Environmental monitoring.
Patient and elderly monitoring.
Flood and forest fire detection.
Disaster relief operations management.
Traffic management.
Smart office, home and car systems.
Space exploration.
Collaborative systems.
Health applications



Telemonitoring of human physiological data
Tracking and monitoring patients and doctors
inside a hospital
Drug administration in hospitals
Factors influencing sensor network
design
Fault tolerance

Some sensor nodes may fail or be blocked due to lack of power, or
have physical damage or environmental interference. The failure of
sensor nodes should not affect the overall task of the sensor network.
This is the reliability or fault tolerance issue.

Fault tolerance is the ability to sustain sensor network functionalities
without any interruption due to sensor node failures.

The reliability Rk(t) or fault tolerance of a sensor node is modeled in
using the Poisson distribution to capture the probability of not having
a failure within the time interval (0,t):
Rk(t) = e – λk t
where λk is the failure rate of sensor node k and t is the time period.
Factors influencing sensor network
design
Production costs

The cost of a single node is very important to justify the overall
cost of the networks.

The cost of a sensor node is a very challenging issue given the
amount of functionalities with a price of much less than a dollar.
Factors influencing sensor network
design
Scalability
 The number of sensor nodes deployed in studying a
phenomenon may be on the order of hundreds or thousands.
 Some times depending on the application we may increase the
number of nodes, New schemes must be able to work with this
number of nodes. They must also utilize the high density of the
sensor networks.
 Scalability measures the density of the sensor nodes.
 Density = µ(R) =(N π R2)/A
where N is the number of scattered sensor nodes in region A,
and R is the radio transmission range. Basically, µ(R) gives the
number of nodes within the transmission radius of each node in
region A.
Factors influencing sensor network
design
Hardware constraints
Hardware components




A sensor node is made up of four basic components, a sensing
unit, a processing unit, a transceiver unit, and a power unit.
additional application-dependent components such as a location
finding system, power generator, and mobilizer.
sensors and analog-to-digital converters (ADCs): The analog
signals produced by the sensors based on the observed
phenomenon are converted to digital signals by the ADC, and
then fed into the processing unit.
The processing unit, which is generally associated with a small
storage unit, manages the procedures that make the sensor node
collaborate with the other nodes to carry out the assigned
sensing tasks.
Hardware components




A transceiver unit connects the node to the network.
Power units may be supported by power scavenging units such as
solar cells.
Most of the sensor network routing techniques and sensing tasks
require knowledge of location with high accuracy. Thus, it is
common that a sensor node has a location finding system.
A mobilizer may sometimes be needed to move sensor nodes
when it is required to carry out the assigned tasks.
Hardware constraints

All of these subunits may need to fit into a matchbox-sized
module.

These nodes must consume extremely low power.

Operate in high volumetric densities have low production cost,
be dispensable and autonomous, operate unattended, and be
adaptive to the environment.
Factors influencing sensor network
design
Sensor network topology :
 Deploying a high number of nodes densely requires careful
handling of topology maintenance
 Pre-deployment and deployment phase : Sensor nodes can be
either thrown in as a mass or placed one by one in the sensor field. They
can be deployed by dropping from a plane, delivered in an artillery shell,
rocket, or missile, and placed one by one by either a human or a robot.
 Post-deployment phase : After deployment, topology changes are
due to change in sensor nodes position, reachability (due to jamming,
noise, moving obstacles, etc.), available energy, malfunctioning, and task
details.
 Re-deployment of additional nodes phase : Additional sensor
nodes can be redeployed at any time to replace malfunctioning nodes or
due to changes in task dynamics.
Factors influencing sensor network
design
Environment

Sensor nodes are densely deployed either very close or directly inside the
phenomenon to be observed. They usually work unattended in remote
geographic areas :
 Interior of a large machinery
 Bottom of an ocean
 Inside a twister
 Surface of an ocean during a tornado
 Biologically or chemically contaminated field
 Battlefield beyond the enemy lines
 Home or a large building
 Large warehouse
 Fast moving vehicles
 Drain or river moving with current.
Factors influencing sensor network
design
Transmission media:
In a multihop sensor network, communicating nodes are linked
by a wireless medium. To enable global operation, the chosen
transmission medium must be available worldwide.
 Radio : The Wireless Integrated Network Sensors (WINS)
architecture uses radio links for communication.
 infrared : Infrared communication is license-free and robust to
interference from electrical devices. Infrared-based transceivers
are cheaper and easier to build
 optical media : Another interesting development is that of the
Smart Dust mote, which is an autonomous sensing, computing,
and communication system that uses the optical medium for
transmission.
Factors influencing sensor network
design
Power consumption:
 The wireless sensor node, being a microelectronic device, can
only be equipped with a limited power source (< 0.5 Ah, 1.2 V)
 In a multihop ad hoc sensor network, each node plays the dual
role of data originator and data router.
 The main task of a sensor node in a sensor field is to detect
events, perform quick local data processing, and then transmit
the data. Power consumption can hence be divided into three
domains:
 Sensing
 Communication
 Data processing
Environmental monitoring





Redwood trees are so large that entire ecosystems exist
within their physical envelope.
Climatic factors determine the rate of photosynthesis,
water and nutrient transport, and growth patterns.
microclimatic structure varies over regions of the
forest.
water transport rates and the scale of respiration may
influence the microclimate around a tree, effectively
creating its own weather
All these factors influence the habitat dynamics of
species existing in and on the tree.
Wireless sensor node for environment
monitoring
Wireless sensor node for environment
monitoring

On top, two incident-light sensors measure total solar radiation,
specifically light and photosynthetically active radiation, the
bands at which chlorophyll are sensitive.

An identical pair of sensors on the bottom, to monitor relative
humidity, barometric pressure, and temperature

Contains a small computer, data storage, battery, and
low-power radio to collect data, process it, and route information
among the nodes and to the outside world
WSN climate data
Results

The measurements show that within the expected daily
cycle, the top of the tree experiences much wider
climatic variation than the forest floor.

These weather fronts create powerful temperature and
moisture gradients that could be instrumental in
understanding growth dynamics, water intake, and
nutrient transport over such large structures, yet they
cannot be observed with sparse instrumentation.
Communication architecture of
sensor networks

The sensor nodes are usually scattered in a
sensor field as shown below:
Sensor communication




Each of these scattered sensor nodes has the
capabilities to collect data and route data back to the
sink.
Data are routed back to the sink by a multi-hop infrastructure less architecture through the sink.
The sink may communicate with the task manager node
via Internet or satellite.
The design of the sensor network is influenced by
many factors, including fault tolerance, scalability, production
costs, operating environment, sensor network topology, hardware
constraints, transmission media, and power consumption.
Data in sensor networks



Sensor networks are predominantly data-centric rather
than address-centric.
Given the similarity in the data obtained by sensors in a
dense cluster, aggregation of the data is performed
locally. Summary or analysis is done by aggregator node
to reduce the bandwidth requirement.
A network hierarchy and clustering of sensor nodes
allows for network scalability, robustness, efficient
resource utilization and lower power consumption.
Data in sensor networks (contd..)





Dissemination of sensor data in an efficient manner requires the
dedicated routing protocols to identify shortest paths.
Redundancy must be accounted for to avoid congestion resulting
from different nodes sending and receiving the same
information.
We need redundancy to ensure reliability.
Data dissemination may be either query driven or based on
continuous updates.
The operation of a sensor network includes a variety of
information processing techniques for the manipulation and
analysis of sensor data, extraction of significant features, along
with the efficient storage and transmission of the important
information.
Communication architecture of
sensor networks

The protocol stack used by sink and all sensor nodes is
as shown below:
Communication architecture of
sensor networks
Application layer
An application layer management protocol makes the
hardware and software of the lower layers transparent
to the sensor network management applications.
 Sensor management protocol (SMP)
 Task assignment and data advertisement protocol
(TADAP)
 Sensor query and data dissemination protocol (SQDDP)
Communication architecture of
sensor networks
Transport layer
 This layer is especially needed when the system is
planned to be accessed through Internet or other
external networks.
 No attempt thus far to propose a scheme or to discuss
the issues related to the transport layer of a sensor
network in literature.
 The communication between user and sink is
TCP/UDP via the Internet or Satellite.
 The communication between the sink and sensor nodes
may be purely by UDP protocols.
Communication architecture of
sensor networks
Network layer
 Power efficiency is always an important consideration.
 Sensor networks are mostly data centric.
 Data aggregation is useful only when it does not hinder
the collaborative effort of the sensor nodes.
 An ideal sensor network has attribute-based addressing
and location awareness.
Communication architecture of
sensor networks
•Maximum available power (PA)
route
•Minimum energy (ME) route
•Minimum hop (MH) route
•Maximum minimum PA node route
Communication architecture of
sensor networks




Maximum available power (PA) route: The route that
has maximum total available power is preferred. (route
4)
Minimum energy (ME) route: The route that consumes
ME to transmit the data packets between the sink and
the sensor node is the ME route. (route 1)
Minimum hop (MH) route: The route that makes the
MH to reach the sink is preferred. (route 3)
Maximum minimum PA node route: The route along
which the minimum PA of the other routes is
preferred. (route 3)
Communication architecture of
sensor networks



Data Aggregation: It can be perceived as a set of
automated methods of combining the data that comes
from many sensor nodes into a set of meaningful
information. It is also known as Data Fusion.
It is a technique used to solve the implosion and
overlap problems in data-centric routing.
In this technique, a sensor network is usually perceived
as a reverse multicast tree as shown in the fig. where the
sink asks the sensor nodes to report the ambient
condition of the phenomena.
Communication architecture of
sensor networks
Data aggregation
Communication architecture of
sensor networks
Data link layer
The data link layer is responsible for the medium
access and error control. It ensures reliable
point-to-point and point-to-multipoint
connections in a communication network.
Communication architecture of
sensor networks
Medium access control
 Creation of the network infrastructure
 Fairly and efficiently share communication
resources between sensor nodes
Communication architecture of
sensor networks
Power saving modes of operation
Operation in a power saving mode is energy
efficient only if the time spent in that mode is
greater than a certain threshold.
Communication architecture of
sensor networks
Error control
 Forward Error Correction (FEC)
 Automatic Repeat Request (ARQ).
Simple error control codes with low-complexity
encoding and decoding might present the best
solutions for sensor networks.
Communication architecture of
sensor networks
Physical layer
The physical layer is responsible for frequency
selection, frequency generation, signal detection,
modulation and data encryption.
Communication architecture of
sensor networks



Power management: This plane manages how a sensor
node uses its power.
Mobility management: This plane detects and registers
the movement of sensor nodes, so a route back to the
user is always maintained and the sensor nodes can
keep track of who are their neighbor sensor nodes.
Task management: This plane is needed, so that sensor
network nodes can work together in a power efficient
way , route data in a mobile sensor network, and share
resources between sensor nodes.
Conclusion


The flexibility, fault tolerance, high sensing
fidelity, low-cost and rapid deployment
characteristics of sensor networks create many
new and exciting application areas for remote
sensing.
In the future, this wide range of application
areas will make sensor networks an integral part
of our lives.
Questions?
1.
2.
3.
What are factors influencing sensor network
design?
What are different components of a sensor
node?
What is data aggregation?
THANK YOU