a paper from ACM SenSys 2015

1. SpinLight: A High Accuracy and
Robust Light Positioning System
for Indoor Applications
B00902069 Chiao Fu

2. Related Works
• Indoor positioning
• Light
• LOS
• Predictable, accurate
• RollingLight
• RF
• Non-LOS
• Less deterministic
• Highly dense deployment
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3. Inspiration
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4. SpinLight
• Spatial beams
• Unique light flash pattern
(infrared)
• No RSS-based ranging
(digital-only)
• Both 2D & 3D
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5. Outline
• System overview
• 2D localization
• 2D localization optimization
• 3D localization
• Evaluation
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6. System Overview
• Assume point light source
• Flash at specific rate
• Hemispherical shade
• 8 rings, 48 cells for each
• Rotate horizontally
• Hollow cell -> 1
Closed cell -> 0
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7. System Overview
• Projection of shade on floor
-> polar coordinate system
• Ring number
• Each ring has unique code
• Cell number
• Count cells from initial direction
• LED flashes in 2 different rate
• Switches when shade’s start point
hits the initial direction
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8. 2D Localization
•
• Leading bits, ring ID bits, extension bits
• No two 0 bits appear together
• Ring ID defined by macro bits
• 1 : 11110, 0 : 11101
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9. 2D Localization
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-> IR from fluorescent lamps at 100 Hz
-> 2 flash rate: 143 Hz & 167 Hz
ring code

10. 2D Localization Optimization
• Find Δθ and Δr && Deal with gray area
• Find Δθ
• Cell 1 see the fraction
• Cell 0
switch flash rate 1 cell later
then see the fraction
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11. 2D Localization Optimization
• Find Δr
• Special 1 cell in extension bits!!
• Close the spherical triangle subarea
• Signal window length
ab == cd -> 
ef != gh -> 
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12. 2D Localization Optimization
• Gray area
• Actually not point light source //more cells, more gray area
• Erroneous reading 0/1 depending on intensity threshold
• Within same ring -> by shifted synchronization
• Across 2 neighbor rings
• Inaccurate estimation of Δθ
• Wrong determination of ring number
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000
001
010
011
100
101
111

13. 3D Localization
• Two light source
• First assume 1 m height
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14. Evaluation
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Location error Effect of distance Effect of reflection
Effect of ambient light Effect of orientation Effect of location optimization

15. Issues
• Coverage
• 3 W -> 95 ㎡, 10 W -> ? ㎡
• Delay
• At most 2 rotation to localize,
depend on speed of the step motor
• Light sensor’s sampling rate
• Energy consumption
• 0.25 mW for prototype
• Coin cell battery -> last month to years
• Mechanical fault tolerance
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16. Question?
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17. Thanks!:D