SmartVLC: When Smart Lighting Meets VLC

Hongjia Wu1, Qing Wang1,2, Jie Xiong3, Marco Zuniga1

1TU Delft 2KU Leuven 3Singapore Management University

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

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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