survey of visible light based backscatter communication...
TRANSCRIPT
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Ju Wang
Jan. 5, 2018
Survey of Visible Light based Backscatter Communication, Sensing
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Visible Light based Backscatter Communication
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Visible Light Backscatter Communication• Retro-VLC: Enabling Battery-free Duplex Visible Light Communication for Mobile and IoT
Applications, in HotMobile’15 (First Visible Light Backscatter Communication paper)
• PassiveVLC: Enabling Practical Visible Light Backscater Communication for Batery-free IoTApplications, in Mobicom’17 (An improvement paper for Retro-VLC)
• Pixelated VLC-Backscattering for Self-Charging Indoor IoT Devices, in IEEE PHOTONICS TECHNOLOGY LETTERS 2017 (An improvement paper for Retro-VLC)
• Passive Communication with Ambient Light, in CoNEXT’16 (A new idea for Visible Light Backscatter Communication)
• Battery-free Visible Light Sensing, in VLCS’17 (using visible light for sensing and RF Backscatter for communication)
• Passive Sensing and Communication Using Visible Light: Taxonomy, Challenges and Opportunities, in arXiv’17 (A short survey paper for Visible Light Backscatter Communication)
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Retro-VLC, in HotMobile’15
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• Motivation:
--Existing VLC systems focus on one-way communications, i.e., from illumination to mobile device.
--This paper enables a battery-free device to perform bi-directional communications over a shared light carrier.
• Basic idea:
--Retro-reflective fabric bounces light back to its source along its incoming direction.
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Retro-VLC, in HotMobile’15
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• System architecture:
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Retro-VLC, in HotMobile’15
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• System architecture:
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Retro-VLC, in HotMobile’15
• Carrier: switching LED at 1MHz.
• Modulation: On/Off keying.
• Maximum distance: 2.6m.
• Field of view (FoV): ±25 degree.
• Uplink data rate: low, ~125 bps.
• Power consumption: reader, 12W; tag, 0.234mw.
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PassiveVLC, in Mobicom’17
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“Seek to improve the data rate of RetroVLC ”
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PassiveVLC, in Mobicom’17
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• Two observations:
--Manchester coding used in RetroVLC is not efciency.
--No need to “fully” switch on/off the LCD to convey a signal.
• PassiveVLC did two improvements:
--Replace Manchester coding with Miller code --> 8x data rate improvement.
Up to 1 kbps on a loss-free uplink within 1 m working distance
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PassiveVLC, in Mobicom’17
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• Two observations:
--Manchester coding used in RetroVLC is not efciency.
--No need to “fully” switch on/off the LCD to convey a signal.
• PassiveVLC did two improvements:
--Design a trend-based modulation--> modulation time reducing, 4 msto 1 ms.
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PassiveVLC, in Mobicom’17
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• I think the technical contributions of this paper are weak, they did not solve the basic challenges:
--Can not work in NLOS, long range, large beam angle.
--Easily distorted by other light sources.
--Still low data rate.
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Pixelated VLC-Backscattering in IEEE PHOTONICS TECHNOLOGY LETTERS 2017
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“Seek to improve the data rate of RetroVLC ”
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Pixelated VLC-Backscattering in IEEE PHOTONICS TECHNOLOGY LETTERS 2017
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(b) The proposed pixelated based system.(a) Past VLC backscatter system architecture.
Multiple smaller VLC backscatters are integrated to generate multi-level signals
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Ambient Light Passive Communication, in CoNEXT’16
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Ambient Light Passive Communication, in CoNEXT’16
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• Key idea:
--Embed data into reflective objects (with different reflective materials) for passive communication
--When object moves, intensity of reflected light changes, altering the light impinging towards receiver.
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Battery-free Visible Light Sensing, in VLCS’17
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• Using solar cells as light sensors. Ambient light as a sensing medium allows tracking of shadows cast by objects.
• Working distance & power: 330m, at a peak power of 20 μWs.
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Visible Light based Sensing
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Key Groups
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Microsoft Research Asia
Feng Zhao Xinyu Zhang
University of California San Diego
Xia Zhou Tian He
Dartmouth College University of Minnesota
• Focuses on Visible Light based localization
• Proposed First Visible Light Backscatter Communication
• Proposed First Visible Light localization
• Focuses on both Visible Light based gesture recognition andCommunication
• Few papers about Visible Light based localization
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The First Visible Light based localization paperNSDI’14
Microsoft Research AsiaFeng Zhao
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Epsilon: A Visible Light Based Positioning System, in NSDI’14
System setup and Performance
• Method: Range-based localization.
• TX: 5 Commercial LEDs.
• RX: 1 Smart phone with light sensor.
• Test area: Office, ~ 3m x 3.5m.
• Accuracy: ~ 0.7m
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Epsilon: A Visible Light Based Positioning System, in NSDI’14
Key Contribution:
• An Optical Channel Model that shows the relationship between light RSS and distance
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Weakness:
• The model only works well within ± 60°
• Requiring light sensor faces squarely upward toward ceiling
Θ=φ=0
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MobiCom’14 The First AoA based Visible Light localization paper
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Luxapose, in MobiCom’14
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System setup and Performance• Method: AoA-based localization.• TX: 5 Commercial LEDs with known locations as landmarks.• RX: 1 Smart phone with camera.• Test area: office room, ~ 71.1 cm x 73.7 cm.• Accuracy: ~ 7 cm
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MobiCom’15 A high localization accuracy paper with errors ~7 mm
Xinyu Zhang
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Near-Field Visible Light Sensing, in Mobicom’15
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System setup and Performance• Method: RSS-model based Location.• TX: 1 LED with known location.• RX: 2 photodetectors (PDs) with known locations.• Test area: office room, ~ 8 cm x 8 cm.• Accuracy: ~ 7 mm
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MobiCom’17
Xinyu Zhang
The AoA based Visible Light localization without a camera
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Pulsar, in Mobicom’17
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System setup and Performance• Method: AoA-based localization.• TX: 4 fluorescent/LED light with known locations.• RX: 2-PD based light sensor.• Test area: indoor, ~ ? cm x ? cm.• Accuracy: ~ 20 cm
Motivation:
Camera is expensive;
PD is much cheaper.
Self-built receiver
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Key Contribution:
• Using RSS to calculate AoA
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Pulsar, in Mobicom’17
The Ratio of RSS at two near by PDs
AoA
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Sensys’17
Tian He
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SmartLight, in Sensys’17
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System setup and Performance• Method: geometrical optical property based localization.• TX: 1 modified LED array with known location.• RX: 1 light sensor.• Test area: office room, ~ 2.5 m x 2.5 m.• Accuracy: ~ 10 cm
Lens
Basic idea:
• Each LED pixel blinks at a unique frequency.
• Locations of LEDs are known for light sensor.
• A sensor receives light from a part of LEDs.
• The location can be estimated based on the geometrical optical property.
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MobiCom’15
Xia Zhou
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Human Sensing Using VLC, in Mobicom’15
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System setup and Performance• Method: Mapping shadow to gesture.• TX: 5 LED with known location.• RX: 324 photodetectors (PDs) with known locations.• Test area: office room, ~ 3m x 3m.• Accuracy: more than 90%
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Human Sensing Using VLC, in Mobicom’15
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Challenge 1: Separating shadows caused by multiple LEDs.Solution: Using the frequency differences of different LEDs.
Solution: Using skeleton model and optimization.
Challenge 2: Mapping 2D shadows to 3D gesture.
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Summary
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• High accuracy: easily achieving sub-meter accuracy due to LoS propagations.
• Limited coverage
--Cost of LED, i.e., requiring unique frequency.
--Limited sensing ability of AoA/Range, e.g., only works within ±60°
High accuracy, but only works within a limited range.