1. Localization in WSN
Localization in WSN

2. Agenda Introduction to WSN Localization Usage GPS .. Why not ?
Localization methods taxonomy
Classifications of Localization Methods
Summary
Future work
References
Localization in WSN

3. Introduction to WSN A large number of self-sufficient nodes
Nodes have sensing capabilities
Can perform simple computations
Can communicate with each other
Localization in WSN

4. Introduction to WSN (Cont.)
Beacon (Anchor) node:
It’s a node that’s aware of it’s location, either through GPS or manual pre-programming during deployment.
Localization in WSN

5. Introduction to WSN (Cont.)
In a Wireless sensor nodes thousands of sensors need to know their position
Many applications need position info:
in-home
forest-fire detection
atmospheric (temperature, pressure, … )
military (target detection, …)
police
Localization in WSN

6. Introduction to WSN (Cont.)
Advantages:
It avoids a lot of wiring
It can accommodate new devices at any time
It's flexible to go through physical partitions
It can be accessed through a centralized monitor
Localization in WSN

7. Introduction to WSN (Cont.)
Disadvantages
It's easy for hackers to hack it as we cant control propagation of waves
Comparatively low speed of communication
Gets distracted by various elements like Blue-tooth
Localization in WSN

8. Localization
Localization is a process to compute the locations of wireless devices in a network
WSN Composed of a large number of inexpensive nodes that are densely deployed in a region of interests to measure certain phenomenon.
The primary objective is to determine the location of the target
Localization in WSN

9. Localization (CONT.)
Localization in WSN

10. Localization (CONT.)
Localization in WSN

11. Usage Coverage Deployment Routing Location service Target tracking
rescue
Localization in WSN

12. GPS .. Why not ?
We need to determine the physical coordinates of a group of sensor nodes in a wireless sensor network (WSN)
Due to application context and massive scale, use of GPS is unrealistic, therefore, sensors need to self-organize a coordinate system
Localization in WSN

13. GPS .. Why not ? (Cont.) Expensive
GPS satellite signals are weak (when compared to, say, cellular phone signals), so it doesn't work as well indoors, underwater, under trees, etc.
The highest accuracy requires line-of-sight from the receiver to the satellite, this is why GPS doesn't work very well in an urban environment
The US DoD (dept of defense) can, at any given time, deny users use of the system (i.e. they degrade/shut down the satellites)
Localization in WSN

14. Localization methods taxonomy
Localization in WSN

15. 1- Target/Source Localization
Most of the source localization methods are focused on the measured signal strength.
To obtain the measurements, the node needs complex calculating process.
Localization in WSN

16. 1- Target/Source Localization (Cont.)
1. The received signal strength of single target/source localization in WSN during time interval t:
Localization in WSN

17. 1- Target/Source Localization (Cont.)
2. The received signal strength of multiple target/source localization in WSN during time interval t:
Localization in WSN

18. 1- Target/Source Localization (Cont.)
The Above methods require transmission of a large amount of data from sensors which may not be feasible under communication constraints.
3-4. The binary sensors sense signals ( infrared, acoustic, light, etc. ) from their vicinity, and they only become active by transmitting a signal if the strength of the sensed signal is above a certain threshold.
Localization in WSN

19. 1- Target/Source Localization (Cont.)
The binary sensor only makes a binary decision (detection or non-detection) regarding the measurement.
Consequently, only its ID needs to be sent to the fusion center when it detects the target. Otherwise, it remains silent.
So, the binary sensor is a low-power and bandwidth-efficient solution for WSN.
Localization in WSN

20. Taxonomy
Localization in WSN

21. 2- Node Self-localization
Range-based Localization: uses the measured distance/angle to estimate the indoor location using geometric principles.
Range-free Localization: uses the connectivity or pattern matching method to estimate the location. Distances are not measured directly but hop counts are used. Once hop counts are determined, distances between nodes are estimated using an average distance per hop and then geometric principles are used to compute location.
Localization in WSN

22. 2-1 Range based localization
Localization in WSN

23. 2-1 Range based localization (Cont.)
Time of arrival: (TOA)
It’s a method that
tries to estimate
distance between 2
nodes using time
based measures.
Accurate but needs synchronization
Localization in WSN

24. 2-1 Range based localization (Cont.)
2. Time Difference Of Arrival: (TDOA)
It’s a method for
determining the distance
between a mobile station
and a nearby synchronized
base station. (Like AT&T)
No synchronization
needed but costly.
TDOA is the location determination method that AT&T uses to locate a caller when they dial 911 from their mobile phone. TDOA calculates the location of a mobile phone by using the difference in the time of arrival of signals at different cell sites.
Localization in WSN

25. 2-1 Range based localization (Cont.)
3. Received Signal Strength Indicator: (RSSI)
Techniques to translate signal strength into distance
Low cost but very
sensitive to noise
Localization in WSN

26. 2-1 Range based localization (Cont.)
4. Angle Of Arrival: (AOA)
It’s a method that allows
each sensor to evaluate
the relative angles
between received radio
signals.
Costly and needs
extensive signal processing.
Localization in WSN

27. 2-2 Range-free localization
DV-Hop is the typical representation
It doesn’t need to measure the absolute distance between the beacon node and unknown node. It uses the average hop distance to approximate the actual distances and reduces the hardware requirements.
Localization in WSN

28. 2-2 Range-free localization (Cont.)
Adv:
Easy to implement and applicable to large network.
Disadv:
The positioning error is correspondingly increased.
Localization in WSN

29. 2-2-1 DV-Hop It is divided into 3 stages: Information broadcast
Distance calculation
Position estimation
Localization in WSN

30. 1-Information broadcast
The beacon nodes broadcast their location information package which includes hop count and is initialized to zero for their neighbors.
The receiver records the minimal hop of each beacon nodes and ignores the larger hop for the same beacon nodes.
The receiver increases the hop count by 1 and transmits it to neighbor nodes.
All the nodes in a network can record the minimal hop counts of each beacon nodes.
Localization in WSN

31. 2-Distance calculation
According to the position of the beacon node and hop count, each beacon node uses the following equation to estimate the actual distance of every hop
Localization in WSN

32. 3- Position estimation
The beacon node will calculate the average distance and broadcast the information to network.
The unknown nodes only record the first average distance and then transmit it to neighbor nodes.
The unknown node calculates its location through.
Localization in WSN

33. 2-2-1 DV-Hop (Cont.) A-B: 15 Anchors B Nodes C A flood network with
own position
avg hop distance
Nodes
count number
of hops to anchors
multiply with avg hop distance
3 hops B
avg hop: 5 3 2 4 1 C A
Localization in WSN

34. 2-2-1 Modified DV-Hop
Localization in WSN

35. 2-2-2 Pattern Matching Localization
Also called map-based or finger print algorithm.
It involves 2 phases:
The received signals at selected locations are recorded in an offline database called radio map.
It works at the online state.
The pattern matching algorithms are used to infer the location of unknown node by matching the current observed signal features to the prerecorded values on the map
Localization in WSN

36. Classifications of Localization Methods
The localization techniques can be classified with respect to various criteria:
Centralized vs Distributed
Range-free vs Range-based
Mobile vs Stationary
Coarse-grained vs fine-grained
Localization in WSN

37. Centralized vs Distributed
Data collected in the whole network are transmitted to the central unit that calculates the estimated location of each node in a network.
Distributed
Computation is distributed among the nodes
Each node estimates its own position based on the local data gathered from its neighbors.
Localization in WSN

38. Range-Free vs Range-Based
Range-Free (connectivity)
Makes no assumption about the availability or validity of such information, and use only connectivity information to locate the entire sensor network.
Hop-Counting Techniques
Range-Based (distance)
Defined by protocols that use absolute point to point distance estimates (range) or angle estimates in location calculation.
Localization in WSN

39. Mobile vs Stationary
Mobile Stationary
Localization in WSN

40. Coarse-grained vs fine-grained
finding approximate coordinates of nodes in a network so it provide lower precision estimates of this coordinates.
Fine-grained:
Determining precisely the coordinates but require much more communication and computation efforts.
Localization in WSN

41. Summary
WSN .. What & Why ?
Distance estimation VS position computation VS localization algorithm
Single/Multiple localization in WSN/WBSN
Calculating the distance between sensor nodes ( TOA – TDOA – RSSI – AOA )
Localization in WSN

42. Summary
Range-based methods require extra hardware therefore have a higher cost but provide more accurate distance measurements, whereas range-free methods use only connectivity information and so are less accurate.
Range-free localization ( DV-Hop , Modified DV-Hop , pattern matching localization )
The localization techniques can be classified with respect to various criteria. They differ on the assumed localization precision, hardware capabilities, measurement and calculation methods, computing organization, the assumed network configuration, architecture, nodes properties and deployment, etc.
Localization in WSN

43. Future Work
Few papers investigate multiple-source localization in WSN and WBSN
Localization in WSN

44. References http://www.hindawi.com/journals/ijdsn/2012/962523/
Localization in WSN

45. References (Cont.) 4. 5. 6. 7.
Localization in WSN

46. Any Questions?
Localization in WSN

47. Thank You !
Localization in WSN