PETER PAZMANY
SEMMELWEIS
CATHOLIC UNIVERSITY
UNIVERSITY
Development of Complex Curricula for Molecular Bionics and Infobionics Programs within a consortial* framework**
Consortium leader
PETER PAZMANY CATHOLIC UNIVERSITY
Consortium members
SEMMELWEIS UNIVERSITY, DIALOG CAMPUS PUBLISHER
The Project has been realised with the support of the European Union and has been co-financed by the European Social Fund ***
**Molekuláris bionika és Infobionika Szakok tananyagának komplex fejlesztése konzorciumi keretben
***A projekt az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósul meg.
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Peter Pazmany Catholic University
Faculty of Information Technology
www.itk.ppke.hu
Ad hoc Sensor Networks
Érzékelő mobilhálózatok
Localization algorithms and strategies for
wireless sensor networks
Lokalizációs algoritmusok és stratégiák vezeték nélküli
hálózatok számára
Dr. Oláh András
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Lecture 9 review
• Technological motivations
• The role of routing
• Algorithmic background: the Bellman-Ford algoirthm and its
distributed operation
• Routing in WSNs
• Packet forwarding in WSNs
• Conclusions
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Outline
•
•
•
•
•
•
•
Motivations of localization
Challenges in WSN
Taxonomy of location systems
Localization algorithms
Accuracy requirements
Available localization systems
Tracking in WSN
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Why is localization important?
• It is a fundamental component for many other services
–
–
–
–
–
GPS does not work everywhere
Smart Systems – devices need to know where they are
Geographic routing & coverage problems
People and asset tracking
Need spatial reference when monitoring spatial phenomena
• In many WSN application we are interested in identifying the
exact location:
– Where has something happened ?
– Where is an Object ?
• Determining the location of the sensor node based on other sensor nodes
with known fixed locations called (beacon nodes)
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Challenges in WSN
• Physical layer imposes measurement challenges
– Multipath, shadowing, sensor imperfections, changes in propagation
properties (RSSI based localization)
• Extensive computation aspects
– Many formulations of localization problems, how do we solve this
optimization problem? We have to solve the problem on a memory
constrained processor.
– How do we solve the problem in a distributed manner?
• Networking and coordination issues
– We are using it for routing [→ see Chapter 9], it means we have routing
support to solve the problem!
• System Integration issues
– How do you build a whole system for localization?
– How do you integrate location services with other applications?
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Real Time Location Systems
• The wireless devices are becoming more and more integrated
into our daily lives.
• Wireless devices are becoming more context aware: a system
is context aware if it uses contexts to provide relevant
information and services (time, location, temperature, speed,
orientation, biometrics, audio/video recordings, etc.) to the
user, where relevancy depends on the user’s tasks.
• Between these variables that define a context, location is
probably the most important inputs that define a specific
situation.
• Localization serves as an enabling technology (Real Time
Location Systems) that makes numerous context-aware
services and applications possible (Location Based Services).
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Taxonomy of location systems
• Signaling scheme
– Infrared signal (inexpensive, low power; it is susceptible against
sunlight; it cannot penetrate through obstructions )
– Optical signal (LoS, low power, it is affected by sunlight, it provides
high accuracies in the short ranges (10m))
– Ultrahang jelek (high accuracies in the short range, inexpensive in LoS
conditions, power hungry)
– Radio frequency (most commonly used, it can penetrate through
obstacles and can propagate to long distances.)
• UWB, CDMA, OFDM, etc.
• Cellular systems, WLAN, WPAN, RFID, WSN
• Location estimation unit
– handset-based (self-positioning, eg.: GPS)
– network-based (remote-positioning, eg.: WSN)
• Indoor versus outdoor localization
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Taxonomy of location systems (cont’)
• Localization type:
– Active Localization: system sends signals to localize target.
– Cooperative Localization: the target cooperates with the system.
– Passive Localization: system deduces location from observation of
signals that are “already present”.
– Blind Localization: system deduces location of target without a priori
knowledge of its characteristics.
•
•
•
•
Centralized versus distributed
Software-based versus hardware-based
Relative coordinate versus absolute coordinate
Based on performance
– accuracy vs. precision, calibration, cost, energy consumption,
sensitivity, self organization capability, delay, datarate, etc.
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Taxonomy of location systems (cont’)
• Position-related parameters:
– received signal strength (RSS)
P(d)=P0−10nlog10(d/d0)
– angle of arrival (AOA)
ri(t)=αs(t − τi) + ni(t)
τi ≈ d/c +(li sin ψ)/c, ahol li = l(Na + 1)/2 − i)
– time-of-arrival (TOA)
correlation based, synchronization is needed
– time difference of arrival (TDOA)
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
The localization algorithm
• Cell ID localization (the nearest reference node)
• Geometrical methods
– Triangulation (at least three nodes)
– Trilateration (in 2D at least three node, in 3Dat least four nodes)
– Multilateration
• Statistical methods
• Fingerprint based or pattern-matching
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Computation models
• Each approach may be appropriate for a different application
• Centralized approaches require routing and leader election
• Fully distributed approach does not have this requirement
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Accuracy requirements
Applications
Range Accuracy
Core apps.
Military
Civil
Sports tracking (NASCAR, horse races, soccer)
150m
10-30cm
Cargo tracking at large depots
300m
300cm
Children in large amusement parks
300m
300cm
Animal tracking
300m
150cm
Military training facilities
300m
30cm
Military search and rescue: lost pilot, man
overboard, coast guard rescue operations
300m
300cm
Tracking guards and prisoners
300m
30cm
Aircraft landing systems
300m
30cm
Tracking firefighters and emergency responders
300m
30cm
Supermarket carts
150m
30cm
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Measurements technologies
• Available Technologies: Bluetooth, Cellular, Satellite, Television, Wi-Fi,
ZigBee, Ultra Wide Band, RFID, Infrared, Ultrasound, Laser
• Ultrasonic ToA
– Common frequencies 25 – 40KHz, range few meters (or tens of meters), avg.
case accuracy ~ 2-5 cm, lobe-shaped beam angle in most of the cases Wideband ultrasonic transducers also available, mostly in prototype phases
• Acoustic ToA
– Range – tens of meters, accuracy =10cm
• RF ToA
– Ubinet UWB claims = ~ 6 inches
• Acoustic AoA
– Average accuracy = ~ 5 degrees (e.g acoustic beamformer, MIT Cricket)
• RSSI based localization
– WSN: Accuracy = 2-3 m, Range = ~ 10m
– 802.11: Accuracy = ~3m
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Available localization systems
Technology
Location method
Accuracy
GPS
ToA satellite based
1-5m
Ekahau
(WLAN)
RSS-based pattern
matching
1m
Microsoft
RADAR
RSS-based pattern
matching
3-4m
LOKI
(WLAN)
Closest AP
Ubisense
TDOA and AOA
Indoor GPS AOA
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Remarks
Expensive, Not works indoors
No extra cost over existing wireless
LAN structure, extensive utilities
Scalability problems, no extra cost over
existing wireless LAN structure
Installed as a free software. Used for
locating the closest restaurant
30cm
Maximum tag-sensor distances greater
than 50m
1mm
Laser positioning system for indoors.
Transmission range expandable from 2
to 300 m.
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Available localization systems: WSN
Technology
Location method
Active
Badges
Infra-red-based proximity
of wearable badges to
predeployed sensors
Active Bats Ultrasound ToA
Cricket
RSS and ultrasoundbased localization
SpotON
RSS-based ad-hoc
localization
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Accuracy
Remarks
Installation costs, cheap tags and
Room-size sensors, sunlight and fluorescent
interference,
9cm
Ceiling sensor installation costs
1m
$10 beacons and receivers,
installation costs
Depends
on cluster
size
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$30 per tag, inaccuracy of RSS
metric
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Tracking in WSN
• Tracking mobile targets involves finding out the location of
mobile targets based on wireless sensor nodes with known
positions (tracing the path).
• Given the locations of the nodes and accurate range
information to the target, it is straightforward to determine the
target's position.
• Traditional tracking applications tend to be split into two
separate phases:
– Localization phase: the network is localized using a specialized
algorithm.
– Tracking phase: after localization completes, target positions are
estimated based on the discovered sensor positions.
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Ad hoc Sensor Networks: Localization algorithms and strategies for
wireless sensor networks
Summary
• Location is probably the most important inputs of context aware systems.
• Common characteristic of numerous location system: each of them is
wireless system.
• Network-based services that integrate a derived estimate of a mobile
device’s location or position with other information so as to provide added
value to the user.
• Most location-based services will include two major actions: (1) Obtaining
the location of a user, and (2) Utilizing this information to provide a
service.
• The accuracy and precision requirements of location-based applications are
highly dependent on the application characteristics.
• There are numerous localization technologies currently available which
have different ranges, accuracy levels, costs, and complexities.
• Next lecture: Applications of ad hoc and sensor networks
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