localization in sensor networking hamid karimi. wireless sensor networks wireless sensor node power...
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LOCALIZATION in Sensor Networking
Hamid Karimi
Wireless sensor networks
Wireless sensor node power supply sensors embedded processor wireless link
Many, cheap sensors wireless easy to install intelligent collaboration low-power long lifetime
The first Sensor Networks
Research started in the 80s by DARPA
Early sensor networks were used in the military
Sensor Network Architecture
SINK
TASK MANAGER
Internet/Satellite
What is Localization?
A mechanism for discovering spatial relationships between objects
Modern applications
Physical security Detecting intruders
Medical Patients in a hospital
Habitat monitoring Wildlife, plants
Environmental Tracking forest fires, pollution
Smart buildings Air traffic control
Required in most applications:Location of the sensor
Reasons for the important of localizationThe localization problem is even more important in wireless sensor
networks for
the following reasons:
1. Many WSN protocols and applications simply assume that all nodes in the system are location-aware.
2. If a sensor is reporting a critical event or data, we must know the location of that sensor.
3. If a WSN is using a geographical routing technique, all of the nodes must be aware of their location.(Location Aided routing)
Initialization
Initialization: Node has no knowledge of its location.
Localization in Sensor Networks
Spatial localization - determining physical
location of a sensor node in the network.
Localization is an essential tool for: The development of low-cost sensor networks
for use in location-aware applications Geographic routing
Possible Implementations/ Computation Models
Determining Location
Direct approaches GPS
Expensive (cost, size, energy) Only works outdoors, on Earth
Configured manually Expensive Not possible for ad hoc, mobile networks
Indirect approaches Small number of anchor nodes
anchor are configured or have GPS Other nodes determine location based on messages
received
GPS
The most obvious solution to this localization problem is to simply equip every node with its own GPS device.
GPS can work only outdoors.
GPS receivers are expensive and not suitable in the construction of small cheap sensor nodes.
A third factor is that it cannot work in the presence of any obstruction like dense foliage etc.
Most of the proposed localization techniques today,depend on recursive trilateration/multilateration techniques
NASA Mars Tumbleweed
Nodes moving, Anchors stationary
Nodes and Anchors moving
Nodes stationary, Anchors moving
Indirect approaches
Steps in Localization
Ranging Phase : distances or angles are measured between known points and the object to be located.
Localization Phase : distances or angle measurements are combined to produce the location of the object.
Refinement Phase : which is an optional step
Most localization techniques consist of tree steps or phases:
Ranging Phase
Received Signal Strength Indicator (RSSI)
Time of Arrival (ToA)
Angle of Arrival (AoA)
Incremental Stepping of Transmission Power
Hybird
Some of the prominent techniques for the Ranging phase include:
Received Signal Strength Indicator (RSSI)
Problem: Irregular signal propagation characteristics (fading, interference, multi-path etc.)
A node receiving a message simply, measures the power of the incoming signal .
An inverse relationship between power and distance can be used to estimate the distance between the nodes.
Time difference of arrival (TDOA)
Idea: Use time difference between arrival of RF and ultrasound signals.
Advantage:
No synchronization Accurate Estimate
Incremental Stepping of Transmission Power
the relationship between a device's transmission power and the maximum distance a signal can transmit.
allows one to gradually increment that transmission power. Once a message is "heard", a bound on the maximum distance between the nodes can be inferred.
Localization Phase
Range Base Schemes Trilateration Multilateration Sum-Dist
Range Free Schemes
Centroid Localization DV-Hop localization
Depending on the method used for ranging, an appropriate localization technique is applied in the second phase. The following localization strategies have been proposed :
Trilateration
: unknown coordinates of node
Subtracting eq. 3 from 1 & 2:
Assuming distances to three points with known location are exactly given
: coordinates of anchor point i, Ri distance to anchor i
Trilateration
Rearranging terms gives a linear equation in
Rewriting as a matrix equation :
Trilateration
MultilaterationAssume some nodes can hear at least three anchors (to perform triangulation), but not all
Problem: Errors accumulate
Sum-Dist
C
A
B
A: 5
5
B: 6+4 = 10
6
4
C: 5+6+4 = 15
6
5
Nodes
add hop distances
require range measurement
Centroid Localization
Receive beacon from anchor nodes.
It is simple and easy to implement
Position is estimated in the center of area where circles from which signal is heard overlap.
DV-HOP
A
B
1
1
1
1
2
2
2
2
2
3
3
3
4
4
A-B: 123 hops
avg hop: 4
Anchors flood network with
known position flood network with avg
hop distance
Nodes count #hops to anchors multiply with avg hop
distance
Local lateration
Refinement
Initial estimate
A
Receive neighbour positions
Broadcast new position
Thank you
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