Localization and
Positioning
By
Lashmi. S (2020252002)
M.E(Communication
System)
Localization
• What is Localization?
• Localization used to identify the location of the sensor node with
respect to space and time.
• Why we need to localize a node?
• Identify the location at which sensor reading originate.
• A sensor reading consist of< time, location, measurement >
• In novel communication protocols that route to geographic areas
instead of ID
Localization(conti..)
Localization in essential
• Necessary for data correlation(eg : Target Tracking).
• Many Mac, routing and other protocols use nodes locations.
• Helps in understanding the utility of a WSN from its coverage area.
• Increasing network lifetime.
Localization(conti..)
• WSN application such as target tracking, habitat monitoring, etc need
to know the location of the sensed information.
• In this application the nodes are deployed with mobility
• Method to find the wireless sensor node position-network installer-
measure location during the node deployment-this method is not
suitable for the scenaries like aircraft
Self Localization Technique
• It is used to determine the geographic position of the node by itself
using WSN initialization process.
• After initialization process, location service algorithm are to find the
location of the nodes. Location service algorithm are used in
geographic routing location aware query processing
Challenges in Localization
• Physical Layer measurements
Info interterms of distance.
message exchange between network node and corresponding
signal strength or timing measurement.
Physical layer measurement
• Result in highly variable distance error since the signal travels a longer
distance.
• Similarly, the angle of arrival can be measured significantly differently
and the node can be projected to locate at a different orientation
• The significantly different ranging measurements result in high
localization error. Moreover, in nonline-of-sight (nlos) environments,
inaccurate ranging measurements cannot be corrected.
• The neighbors that lead to inaccurate measurements need to be
detected and excluded from localization calculations.
Computational Constraints
• Local information from several neighbor nodes -distance, orientation, or
connectivity combined to provide location estimates minimize erroneous
information from a single measurement through multiple measurements.
• Individual measurements can be regarded as constraints for an
optimization problem.
• Maximum likelihood (ML) techniques-highly accurate location.
• Individual sensor nodes can be addressed through centralized solutions.
• Incur high communication overhead and create single point-of-failure
problems.
• Simple and distributed localization algorithms
Low-End Sensor Network
• Sensors - errors in distance or orientation estimation.
• Rss - noisy due to transceiver imperfections.
• Low-end crystals are used, ranging estimates, which depend on timing
measurements, result in erroneous results.
• Space limitations on the embedded system board, the required
diversity may not be achieved for angle-of-arrival measurements.
• Frequent node failures- a node disconnect from the network for some
amount of time or permanently
Lack of GPS
• It is used to locate the wireless sensor nodes autonomously within
few meters accuracy by listening to signals from the number of
satellites and assistive terrestrial transmitters.
• Issues in GPS:
• Costly
• Power Consumption
• Will not work well with indoor application
• Will not work well under foliage
Node Position Identification
• METHODS
Proximity method
Angle based Method
Trilateration and triangulation
Range based method
Proximity method
• This method uses neighbor node information to find the position of node.
• It decide whether a node want to find the position or location is in the
proximity of an Anchor.
• Anchor – are the nodes know their own position in the absolute coordinate
system. rotated, translated and scaled to a relative co-ordinate to coincide
with absolute coordinate system.
• Anchor are also called as beacons or landmarks.
• The restriction of infrared communication provide simple info about the
room.
• The method is used to approximate positioning when a node can analyze the
proximity information of several overlapping anchors
Trilateration and triangulation
• The method uses the geometric properties of the given scenario to find the
position of the node.
• The communication between two node allows to extract information about the
geometric properties.
• The distance between two nodes or the angle in a triangle is used to derive the
info about position of node.
• Lateration - If the distance between two node obtain the information of position
of node.
• This is ranging technique is used to find distance between of sender and receiver.
• Angulation- if the angle between two nodes is used to obtain the info about the
position of node.
• To estimate the distance the range of radio communication device is
important.
• This estimated if the distance between sender and receiver is
measured at the receiver.
Ranging Techniques
• Received Signal strength indicator
By using this method is used to estimate the RF signal strength at the receiver
or
Effects:
Fast fading
Shadowing
Multipath fading
Mobility
Time of arrival (TOA)
• Time of flight
• Transmission time at the sender, time of arrival at the receiver
• Propagation speed known-propagation time and distance estimate.
• Requires high resolution clocks to produce accurate results.
• Propagation speed depends on Temperature and humidity
TOA-Two Types
Active:
• The receiver transmits a ranging packet, which is immediately
responded to by a transmitter.
• The round-trip time is used to estimate the distance between the nodes.
Passive:
• In this case, the transmitter and receiver measurements are made
separately.
• Accordingly, a transmitter sends a beacon signal, which is used by the
receiver to estimate the delay
Time difference of arrival
• This approach uses Two transmission medium of very different
propagation speeds.
• If sender starts an ultrasound transmission and a radio
transmission simultaneously, the receiver can use the arrival of
radio transmission to start measuring the time of arrival of
ultrasound transmission ignoring the propagation time.
• It needs two sender and receiver on each node
• This approach is better accuracy than RSSI approach
Comparison-Localization
Schemes
Localization Techniques Accurancy(in meters) Limitation
used
GPS 2 to 15 Indoor localization is not
possible in many cases
Proximity method 1 to 30 Depends on the Range of
signal used
Angle based method 1 to 8 Requires Special Antenna
Range based method 4 to 10 Require special hardware
and Time synchronization
Thank you
