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SmartVLC: When Smart Lighting Meets VLC
Hongjia Wu1, Qing Wang1,2, Jie Xiong3, Marco Zuniga1
1TU Delft 2KU Leuven 3Singapore Management University
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Background - VLC
Visible Light Communication (VLC): transmit data wirelessly using the artificial light(i.e., LED light) and is flickering-free for users.
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Background - Smart Lighting
Smart Lighting: the LED light changes with ambient light, to keep the totalillumination constant within an area-of-interest
more ambient lightÐ→ less LED light
less ambient lightÐ→ more LED light
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VLC and Smart Lighting in Action
Basic requirements� Smart lighting : fine-grained dimming levels� Visible Light Communication (VLC): optimized throughput
State-of-the-Art (SoA) solutions & Objective of this work
LED’s brightness (dimming level)
Syst
em th
roug
hput
Strong ambient light Weak ambient light
SoA-1SoA-2This work
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Related Work
SoA-1 (OOK-CT): On-Off-Keying (OOK) with Compensation Time
0 Tt
Data Compensation time
0 Tt
Data Compensation time
Dimming level: 40% Dimming level: 20%
SoA-2 (MPPM): Multiple Pulse-Position-Modulation
0 Tt
Choose 2 from 10: 45 possibilities
0 Tt
Choose 4 from 10: 210 possibilities
Dimming level: 40% Dimming level: 20%
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Next Subsection
1 Motivation
2 SmartVLCDesignImplementation
3 Evaluation
4 Conclusion
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Basic Requirements
� Smart lighting : fine-grained dimming levels
� VLC : optimized throughput
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1. Support Fine-grained Resolutions
Increasing the N in MPPM does NOT work!
N ↑ Ô⇒ Symbol Error Rate ↑
Symbol: N1 time slots
à large N …
Symbol: N2 time slots
0 0.2 0.4 0.6 0.8 1
Dimming level of the LED
0
2
4
6S
ym
bo
l E
rro
r R
ate
(S
ER
) 10-3N=10
N=30
N=50
N=80
N=120
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1. Support Fine-grained Resolutions
Proposed solution
Use multiplexing to achieve high resolutions.
t25%
t20%
t30%
After multiplexing, we are able to capture all the brightness.Before multiplexing (N = 10)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Dimming level of the LED (N=10)
0.2
0.3
0.4
0.5
0.6
0.7
Nor
mal
ized
dat
a ra
te
After multiplexing (N = 10)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Dimming level of the LED (N=10)
0.2
0.3
0.4
0.5
0.6
0.7
Nor
mal
ized
dat
a ra
teSmartVLC 9/26
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Basic Requirements
� Smart lighting : fine-grained dimming levelsSOLVED by multiplexing
� VLC : optimized throughput
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2. Increase System Throughput
Symbol definition
� S ∶< N, l >, N is number of slots, l is the brightnesse.g. S1 ∶< 10,20% >, S2 ∶< 10,30% >How about S1 ∶< 9,20% >, S2 ∶< 11,30% > ?
t
20%
t
30%
Obtain the dimming level in between of 20% and 30 %
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2. Increase System Throughput
Proposed solution
Adaptive Multiple Pulse-Position-Modulation (AMPPM): use super-symbols.
0
…
𝑆" 𝑁", 𝑙" 𝑆& 𝑁&, 𝑙&
…
𝑆& 𝑁&, 𝑙&
Super-symbol:⟨𝑆" 𝑁",𝑙" ,𝑚",𝑆& 𝑁&, 𝑙& ,𝑚&⟩
𝑆" 𝑁", 𝑙"
𝑡
Requirement: find the proper < N1, l1 > and < N2, l2 > to compose super-symbols foreach required dimming level.
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2. Increase System Throughput
How to find < N1, l1 > and < N2, l2 >?� Step 1: Collect available symbols
0 0.2 0.4 0.6 0.8 1Dimming level of the LED
0
0.5
1
1.5
2
2.5
Sym
bol E
rror
Rat
e (S
ER
) 10-3
upper bound
N=10N=30N=50
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2. Increase System Throughput
How to find < N1, l1 > and < N2, l2 >?� Step 2: Calculate the normalized data rate for all the collected symbols
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2. Increase System Throughput
How to find < N1, l1 > and < N2, l2 >?� Step 3: Obtain the optimal combination via multiplexing and slope-based selection.
0.5 0.55 0.6 0.65 0.7Dimming level of the LED
0.7
0.75
0.8
0.85
0.88
Nor
mal
ized
dat
a ra
te
N = 10N = 11N = 12N = 13N = 14N = 15N = 16N = 17N = 18N = 19N = 20N = 21
without multiplexing
AMPPM (with multiplexing)
S(21,0.571)S(21,0.524)
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Basic Requirements
� Smart lighting : fine-grained dimming levelsSOLVED by multiplexing
� VLC : optimized throughputSOLVED by AMPPM
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Recap
LED lightIntensity Time
Compensation-based approach
Compensation-free approach
Our proposed approach
Data Compensation
Data (decoding unit)
average
Data (decoding unit) Data (decoding unit) Data (decoding unit)
average
average
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Next Subsection
1 Motivation
2 SmartVLCDesignImplementation
3 Evaluation
4 Conclusion
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3. Implementation
Available platforms
� High-end: USRP (≈ 5000$), WARP (4900$)� Low-end: Arduino (≈20e), BeagleBone Black (BBB, ≈65e), Raspberry Pi (≈40e)
BBB is selected in this project
� PRUs (similar to micro-controllers): BBB has two 200 MHz, 32-bit PRUs.Used for sampling and operating LEDs.
DataBridgeARM PRU
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3. Implementation
Diagram of the front-end Transmitter and Receiver
Photodiode
BBB MOSFET LED
Power
Ambientlight
Transmitter
Photodiode
Amplifier ADC
BBB
Receiver
Snapshot of the prototype
Transmitter Receiver
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Next Subsection
1 Motivation
2 SmartVLCDesignImplementation
3 Evaluation
4 Conclusion
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Evaluation: Static Scenario
Setup: fix the window blind Results: throughput vs. distance
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Distance (m)
0
20
40
60
80
100
120
Thr
ough
put (
Kbp
s)
dimming level=0.18dimming level=0.5dimming level=0.7
Observations� Reliable communication within 3.6 meters� Maximum throughput is ≈ 107 Kbps (dimming level = 0.5)
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Evaluation: Dynamic Scenario
Setup: lift the window blind Results: throughput vs.at a constant speed ambient light changes
0 10 20 30 40 50 60 70Time (second)
50
60
70
80
90
100
110
Thr
ough
put (
Kbp
s)
Ambient light: weak Ð→ strongObservations
� The ambient light does not change averagely.
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Evaluation: Comparison
Comparison with OOK-CT and MPPM
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Dimming level of the LED
20
40
60
80
100
120
Thr
ough
put (
Kbp
s)AMPPMOOK-CTMPPM
Observations� AMPPM outperforms OOK-CT (increases the throughput by 40% on average)� AMPPM outperforms MPPM (provides non-flickering & increases the throughput by
12% on average)
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Conclusion
Co-design smart lighting and VLC:
1 AMPPM: fine-grained resolution & high throughput
2 Implementation: low-end platform1
3 Evaluation: static & dynamic scenarios
4 Others: heuristic coding scheme, brightness adaptation...
1Cited by OpenVLC 1.2
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Looking for PhD position!
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