Wireless sensor networks

Sandra Atijas

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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 bi-directional, 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

• The ZephyrLIFE™ Hospital system has been designed to make remote patient monitoring

• ZephyrLIFE™ Hospital is a comprehensive system that combines

multi-parameter 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

ZephyrLIFE™ Hospital

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ZephyrLIFE™ Hospital system

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

ZephyrLIFE™ Hospital is a tool that may :

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• 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 stand-alone 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

ZephyrLIFE™ Hospital – system components

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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