Introduction to Theory and Applications of Self Organizing
Wireless Sensor Networks
Vijay K. Devabhaktuni & James W. Haslett
Department of Electrical and Computer Engineering
University of Calgary
13 July 2004
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Agenda
Introduction
Self Organizing Wireless Sensor Networks
Experimental System
Wireless Sensor Networks in Patient Monitoring
Demonstration
Summary
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Wireless Sensor Network (WSN)
A wireless sensor network consists of a large number of nodes deployed in the environment being sensed and controlled through wireless communication.
Typically, a WSN consists of
• A number of remote nodes (we refer to them as motes)
• Base station
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Features:The remote nodes self-assemble into a network.
The sensor information is propagated to the base station.
Nodes collaborate i.e. intermediate nodes assist distant nodes to reach the base station.
Routing Tree Link
Connectivity
Base Station
Self Organizing WSN
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Highlights
• Micro-sensors, on-board processing and wireless interface are all possible at very small scale!
• WSN are able to monitor a phenomena up-close
• Spatio-temporally dense environmental monitoring becomes a reality
• Networked sensing can reveal certain previously unobservable phenomena of our nature
Seismic structure response
Contaminant transportation
Marine microorganisms
Eco-system’s biocomplexity
Application Domains
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Sensor ADC Radio
Battery
Event detectionWireless communication with other nodes & base
In-node processing
Mote: Structure & Function
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Enabling TechnologiesTechnological advances have facilitated
• Smaller & cheaper electronic components
• Systems on a single chip
• Integrated low-power communication modules
The above trends enabled WSN characterized by
• Smaller physical size
• Multi-functional behavior & concurrent operation
• Wireless communication
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UCLA, 1996 UCLA, 1998
Sensoria, 2001UCB, 2000
(Crossbow Tech.)
It’s Just a Beginning
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Time
log
(p
eo
ple
pe
r c
om
pu
ter)
“Streaming informationto/fromphysical world”
Number crunchingData storage
ProductivityInteractive
Mainframe
Minicomputer
Workstation
PC
Laptop
PDA
Roadmap
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Flexible integration of sensors
Low-cost & energy-efficient processors
Robust communication over radio
Lifetime source with each mote
A Dream Network!
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4× Mica2 Motes
3× Sensor Boards(MTS300)
Mote to PC Interfaceand Programming Board
(MIB500)
2× Prototyping Boards(MDA500)
4× Mica2Dot Motes
Experimental Hardware
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Generations of Crossbow Motes
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Mica2dot
• Battery
• Memory and Processor
• Sensor modules (externally integrated)
• 916/433 radio transceiver
• 10-bit ADC
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Base Station
Base station includes an interface board that allows
• Mote connectivity
• RS-232 serial programming interface
• Aggregation of network data on a PC
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Sensor interfacing
Radio messaging
Routing
Power management
Time
Debug
Required Software Services
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Developed taking the following aspects into account
• Efficient resource utilization
• Small foot print to run on small processors
Key Features:
• Set of services
• Simple operating system
• Open-source development environment
• nesC programming language
Tiny Operating System (TinyOS)
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Designed for low-power ad hoc WSNResponsive to stimuli, event oriented, scaleable
Key elementsSensing, computation, communication, power
Resource constrainedPower, memory, processing
Adapt to changing technologyModularity & re-use
TinyOS Architecture
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Dialect of C
TOS syntax and structure aware– Variables, tasks, calls, events, signals– Component wiring
A pre-processor– nesC output is a c program file, which is
compiled and linked using gcc tool
nesC - The TinyOS Language
Application Example
A Wireless Patient Monitoring System for the Ward of the 21st Centuryof the Calgary Foothills Hospital
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Doctors wish to continuously monitor variations in
• Temperature
• Heart rate
• Blood oxygenation
• Respiratory rate
Toward this end, we developed a wireless framework.
Patient’s Vital Medical Parameters
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The Comprehensive Wireless Framework
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Key Features
The framework includes
Real-time sensing of patient’s vital parameters using precision-sensors interfaced to the motes
Wireless transmission of such critical information over radio frequencies to the base-station
Subsequent data processing on a PC to allow detection of medical emergencies and alerting of medical staff
Note: Emergency detection is enabled using neural networks
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Deliverables
A self-organizing wireless system capable of continuous patient-monitoring
Patients can move about in the hospital space, thanks to the “multi-hop” feature of WSN
A smart hospital bed with automation in terms of emergency detection
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Temperature Sensor
Ear temperature is quick to read and reliable!
Our initial temperature sensor design involved:
• Thermistor modeling
• Linearization of output voltage
• Initial prototype is operational
• Future work will include packaging of thermistor using a silicon enclosure to protect from ear wax, and other non-intrusive methods of measuring body temperature
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Heart Rate & Blood Oxygenation
This instrument is being interfaced to a wireless mote
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Potential applications for Ad hoc WSN are vast
Low-power transceiver designs become essential
• “Low-power” versus “Performance”
Fully-integrated low-power relaxation VCO• Ken Townsend presented measured results
Low-Power Transceivers
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ADXL202AE dual-axis accelerometers (±2g) from Analog Devices are interfaced to the motes
Mica2dot motes are programmed to read sensor data via ADC3 and wirelessly transmit such data
Nominal reading of sensors is +1500mV at 0g. Sensitivity characteristic is ±150mV/g
Targeted application is the R&D of 6-axis motion of human feet that helps understand Parkinson’s
Concept Demonstration
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(1324,1245)
Two types of nodes– Tripwire nodes
that always sense• Low-power
presence sensing
– Tracker nodes that sense on-demand
Future of Power Management
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Acknowledgements
NSERC
iCORE
TRLabs
Calgary Health Region
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Conclusions
In this project, WSN technology is exploited for developing a framework for wireless patient-monitoring.
Results are expected to significantly help the healthcare personnel to cope with today’s shortage of resources.
The WSN paradigm and its advancements promise many other key applications in the healthcare sector.
The research area opens the doors for novel R&D activities in the microelectronics arena.