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8/12/2019 ICUFN-TDoA Based Indor Visible Light Positioning System
http://slidepdf.com/reader/full/icufn-tdoa-based-indor-visible-light-positioning-system 1/19
8/12/2019 ICUFN-TDoA Based Indor Visible Light Positioning System
http://slidepdf.com/reader/full/icufn-tdoa-based-indor-visible-light-positioning-system 2/19
Current approaches for indoor positioning
There is no standard technique for indoor positioning
Problem with current techniques
Availability
Security
Safety
Cost
Using visible light can overcome these limitations
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ULTRA SOUND
8/12/2019 ICUFN-TDoA Based Indor Visible Light Positioning System
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Basis concept of indoor visible light positioning systemMobile node uses received signals from multiple transmitters to locate its own position
Pilot signals are visible light
Transmitters are LED lamps installed on the ceiling
Mobile node uses photo diode or image sensor to receive light
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Advantage of using visible light for indoor positioningAlways available
Visible light is free
Lighting systems are installed in every building
High secure
The visible light cannot go beyond the roomSafe
Safe for using in hospital, airplanes or hazardous environments
Low cost
LED chips are inexpensive and has long lifetime
The system undertakes both function of positioning and illuminating
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8/12/2019 ICUFN-TDoA Based Indor Visible Light Positioning System
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Candidate for indoor visible light positioning techniqueReceived signal strength (RSS)
Low accuracy due to complicated effects of reflections in the room
Time of arrival (TOA)
Require the synchronization between transmitter and receiver (difficult)
Angle of arrival (AOA)Can achieve high accuracy
But require deploying an array of image sensors (expensive)
Time difference of arrival (TDOA)
Only synchronization between transmitters is required (easy)
Just require to use a single photo diode at receiver (inexpensive)
Reflected light has small impact on the accuracy
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8/12/2019 ICUFN-TDoA Based Indor Visible Light Positioning System
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TDOA positioning in 2DMathematical background
A hyperbola is a locus of pointswhere the absolute value of thedifference of the 2D-distancesto the two foci is a constant.
Positioning from TDOA
3 anchors with knows positions
(at least) are required to find a2D-position from a couple ofTDOAs
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r1
Anchor 2
Anchor 3
Anchor 1
r2
r3
r3-r1
r3-r2
8/12/2019 ICUFN-TDoA Based Indor Visible Light Positioning System
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TDOA positioning in 3DMathematical background
A hyperboloid is a locus of pointswhere the absolute value of thedifference of the 3D-distances tothe two foci is a constant.
Positioning from TDOAs
4 anchors with knows positions (at
least) are required to find a3D-position from a couple ofTDOAs
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Lighting placement
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Pilot signal generation schemeEach LED panel transmits a single square pulse of signal after aguard time period
All signals have the same pulse width
All signals have the same guard time period
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Detection methodReceived signal is a series of pilot signals
Cross-correlation is used to detect each single signal in this series
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Estimate receiver’s position with known signal IDTime differences of arrival is obtained by using cross-correlation
Distance difference from receiver to two transmitters specifies aunique hyperboloid that the receiver lies in
These hyperboloids intersect with the Z-plane of receiver height
and creates a unique conic in 2-D plane containing the receiver
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Estimate receiver’s position without knowing signal ID When a series of signals is received, the possible ID combinations of these signals can be guessed
There is only N possible combinations of signal ID if N LED panelsare used
With K received pilot signals, there are K-1 time differencesK-1 conics that the receiver lies in are found
There are up to intersections can be found
If combination of signal ID is correct, these intersection are converged
Otherwise, these intersections are diverged
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1
2
K
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Estimate receiver’s position without knowing signal ID
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Simulation environment
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Simulation results
At most region in the room, the estimation error is less than 10cm
The average distance error is 3.6cm
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Observation through the simulationThe error is greater when the signal is weaker
This is because the stronger pulse can be detected with less error
The error is greater at the corner than that at the center
This is because the conics specified by TDOA is more curve at the
corner than at the center
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Stronger pulses can be detected with less errorThe conic get curved when the receiver moves
away from the bisector of two transmitters.
8/12/2019 ICUFN-TDoA Based Indor Visible Light Positioning System
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Solution to reduce estimation errorOnly use strongest signals
Move transmitter nearer to the corner
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