Wireless sensor networks
Sandra Atijas
Agenda
• Introduction
• Characteristics
• Network architecture
– Sensor node structure
• Network Applications
• Network Design Challenges
• Conclusion
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Introduction
• Wireless sensor networks (WSNs) have been
widely considered as one of the most
important technologies for the 21st century
• Sensors provide unique opportunities for a
variety of civilian and military applications,
but also for other applications
• WSNs are different from traditional wireless
communication networks
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Description of the problem
• WSN consists of spatially distributed autonomous
sensors to monitor physical or environmental
conditions, such as temperature, sound, pressure
• Sensors cooperatively pass their data through the
network to a main location
• The more and more modern networks are bidirectional, enabling control of sensor activity
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What are sensors?
• Devices are capable of detecting change:
– Temperature
– Pressure
– Humidity
– Sound
– And Many more …
Magnetometer sensor
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WSNs characteristics
• Dense Node Deployment
• Battery Powered Sensor Nodes
• Self – Configurable
• Frequent Topology Change, Unreliable Sensor
Node
• Severe Energy, Computation and Storage
Constraints
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Dense Node Deployment
•
•
•
•
The WSN is network built of low-cost, low-power,
multifunctional sensor nodes – from a few to several
hundreds or even thousands (much larger than that of
conventional wireless networks)
Sensor nodes are densely deployed in a geographical
field
Each node is connected to one (or sometimes several)
sensors
Each such sensor network node has typically several
parts: a radio transceiver with an internal antenna or
connection to an external antenna, a microcontroller,
an electronic circuit for interfacing with the sensors
and an energy source
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Battery Powered Sensor Nodes
•
Sensor nodes are usually powered by battery and
therefore they are have limited in power capacity
•
Usually it is difficult and often impossible to change
and recharge the batteries for these nodes
•
The lifetime of a sensor network largely depends on
the lifetime of its sensor nodes
•
There are other possible energy sources - energy
harvesting modules, secondary communication
interface
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Self – Configurable
• Sensor nodes are often randomly deployed
without careful planning and engineering
• Due to that fact, they have to be able to
organize and configure themselves into a
communication network
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Frequent Topology Change, Unreliable
Sensor Nodes
• The topology of a sensor network changes often
due to node failure, mobility, damage, channel
fading...
• These sensor nodes are prone to physical
damages and failures
• Most of them are stationary after deployment,
but in some applications they can be mobile
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Severe Energy, Computation and Storage
Constraints
• Sensor nodes are highly limited in energy,
computation and storage capacities
Solar energy for sensor node
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Network
• The topology of the WSNs can vary from a simple
star network to an advanced multi-hop wireless
network
• The propagation technique between the hops of
the network can be routing or flooding
– Routing is the process of selecting best paths in a network along
which to send network traffic
– A flooding algorithm is an algorithm for distributing material to
every part of a graph
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Sensor Network Architecture (1)
• Sensor network typically consists of a large number of
sensor nodes densely deployed in a region of interest
and one or more data sinks or base stations that are
located close to, or inside the sensing region
• Sink sends queries or commands to the sensor nodes in
sensing region while the sensor nodes collaborate to
achieve the sensing task and send the sensed data to the
sink
• Sink serves as a gateway to outside networks Internet. It
collects data from sensor nodes, performs simple
processing on the collected data and then sends
relevant information (or processed data) via the Internet
to the users who requested it
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Sensor network architecture (2)
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Single-hop network architecture
• To send the data to the sink, each sensor node can use
single-hop long-distance transmission
• Expensive. The energy consumed for communication is
much higher than that for sensing and computation
• It is desired to reduce the amount of traffic and
transmission distance in order to increase
energy savings and prolong network lifetime
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Multi-hop network architecture (1)
• Multi-hop short-distance communication is highly
preferred
• This is possible thanks to the fact that, in most sensor
networks, sensor nodes are close to each other
• Sensor node transmits (sensed) data toward the sink via
one or more intermediate nodes, which can reduce
energy consumption for communication
• There are two types of architecture:
– Flat Architecture
– Hierarchical Architecture
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Multi-hop network architecture (2)
• Flat Architecture
– Each node plays the same role in performing a
sensing task
– All sensor nodes are peers
– It is feasible to assign a global identifier to each node
in a sensor network
– Data sink transmit queries to all sensor nodes in the
sensing region via flooding
– Only the sensor nodes that have data matching the
query will respond to sink
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Multi-hop network architecture (3)
• Hierarchical Architecture
– Sensor nodes are organized into clusters, where the
cluster members send their data to the cluster heads
– Cluster heads transmit the data to the sink
– Nodes with higher energy can be selected as a
cluster head to process data from its cluster members
to the sink
– In addition to reduction the energy consumption for
communication, this process also balance traffic load
and improve scalability
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Sensor Node Structure
• A sensing unit
• A processing unit
• A communication unit
• A power unit
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Network Applications (1)
• Health Care Application
• Home Intelligence
• Security and Surveillance
• Military Applications
• Industrial Process Control
• Environmental Monitoring
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Health Care Application
• To monitor and track patients for health cure
purposes
– Behaviour Monitoring – Sensors deployed in a
patient’s home to monitor the behaviours of patient
– Medical Monitoring – Sensors integrated into a
wireless area network to monitor vital signs,
environmental parameters…
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Health Care – Hospital - Application
ZephyrLIFE™ Hospital
•
The ZephyrLIFE™ Hospital system has been designed to make remote patient
monitoring
•
ZephyrLIFE™ Hospital is a comprehensive system that combines multiparameter vital signs, encrypted wireless communications and an intuitive
notification engine
•
This system allows seamless, simultaneous monitoring of multiple users
•
Collected information are visualized and updated every minute
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ZephyrLIFE™ Hospital system
ZephyrLIFE™ Hospital is a tool that may :
Aid in early detection of:
• Respiratory changes
• Heart rate changes with rhythm displays
• Systemic infection
Enhance Risk Management:
• Activity alerting and trends leading to fall prevention
• Decubitus prevention via activity and turn-time monitoring
Assist in Chronic Disease Management
• Congestive Heart Failure, Post Myocardial intervention
rehabilitation, Chronic Obstructive Pulmonary Disease, Diabetes
management
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ZephyrLIFE™ Hospital – system components
• Zephyr BioPatch™- is an FDA Class II prescription
device which consists of a rechargeable BioModule™
sensor and holder. Attached to patients using
standard electrodes
• ZephyrLIFE™ ECHO Mesh Radio System – is a standalone mesh radio system that allows the Zephyr
BioPatch™ to communicate with the ZephyrLIFE™
Central Monitoring Station securely while providing
immediate event based alerting
• ZephyrLIFE™ Central Monitoring Station - provides a
secure touch-screen terminal where nurses, clinicians
and other healthcare team members can monitor
their patients’ health continuously
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Defense solutions
• Zephyr’s PSM (Physiological Status Monitoring) Defense
system gives you real-time physical status of persons
operating in high stress and extreme environments
• PSM measures vital signs in the context of position and
movement, and interprets the signals to help determine
whether persons are tired, dehydrated, injured or
healthy
• With PSM Defense
ECHO – conditioning,
effort and stress can be
quantified, recorded and
analysed
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Home Intelligence
• To provide more convenient and intelligent
living environment for human beings
– Smart Home – wireless sensor embedded into a home
and connected to form an autonomous home network
– Remote Metering - wireless sensor remotely used to
read utility meters at home (water, gas, electricity..)
and than send to the remote center through wireless
network
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Security and Surveillance
• Acoustic and video sensors can be deployed in
buildings, airports, subways
• To provide timely
alarms and protection
from potential attacks
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Military Applications
• Integral part of military command, control,
communication and intelligence systems
– Battlefield Monitoring – Sensors can be deployed in
a battlefield to monitor presence of forces
– Object Protection - Sensors nodes can be deployed
around sensitive objects for protection purpose
– Remote Sensing – Sensors deployed for remote
sensing of nuclear, biological
and chemical weapons, detection
of potential terrorist attacks…
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Industrial Process Control
• To monitor manufacturing processes or the
condition of manufacturing equipment
– Tiny sensors embedded into a region of a machine
– Chemical plants
– Oil refiners
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Environmental Monitoring
• Great Duck Island
– 190 sensing nodes deployed throughout the
island relay data temperature, pressure, and
humidity to a central device
– Data was made available on the Internet
through a satellite link
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Network Design Challenges
• Limited Energy Capacity
• Limited Hardware Resources
• Massive and Random Deployment
• Dynamic and Unreliable Environment
• Diverse Applications
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Conclusion
• It is predicted that in the near future
WSNs will be widely used and
revolutionize the way we live, work and
interact with physical work
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Wireless Sensor Networks
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