SmartVLC: When Smart Lighting Meets VLC Hongjia Wu 1 , Qing Wang 1 , - - PowerPoint PPT Presentation

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 total illumination constant within an area-of-interest more ambient light

• → less LED light

less ambient light

• → more LED light

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VLC and Smart Lighting in Action

Basic requirements

❼ Smart lighting: fine-grained dimming levels ❼ Visible Light Communication (VLC): optimized throughput

State-of-the-Art (SoA) solutions & Objective of this work LED’s brightness (dimming level) System throughput Strong ambient light Weak ambient light SoA-1 SoA-2 This work

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Related Work

SoA-1 (OOK-CT): On-Off-Keying (OOK) with Compensation Time

T

t

Data Compensation time

T

t

Data Compensation time

Dimming level: 40% Dimming level: 20%

SoA-2 (MPPM): Multiple Pulse-Position-Modulation

T

t

Choose 2 from 10: 45 possibilities

T

t

Choose 4 from 10: 210 possibilities Dimming level: 40% Dimming level: 20%

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Next Subsection

1 Motivation 2 SmartVLC

Design Implementation

3 Evaluation 4 Conclusion

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Basic Requirements

❼ Smart lighting: fine-grained dimming levels ❼ VLC: optimized throughput

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• 1. Support Fine-grained Resolutions

Increasing the N in MPPM does NOT work!

N ↑ ⇒ Symbol Error Rate ↑

Symbol: N1 time slots

à large N

…

Symbol: N2 time slots 0.2 0.4 0.6 0.8 1

Dimming level of the LED

2 4 6

Symbol Error Rate (SER)

10-3

N=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.

t

25%

t

20%

t

30%

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 0.9

Dimming level of the LED (N=10)

0.2 0.3 0.4 0.5 0.6 0.7

Normalized data rate

After multiplexing (N = 10)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Dimming level of the LED (N=10)

0.2 0.3 0.4 0.5 0.6 0.7

Normalized data rate

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Basic Requirements

❼ Smart lighting: fine-grained dimming levels

SOLVED by multiplexing

❼ VLC: optimized throughput

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• 2. Increase System Throughput

Symbol definition

❼ S ∶< N,l >, N is number of slots, l is the brightness

e.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.

…

𝑇" 𝑂

",𝑚"

𝑇& 𝑂&,𝑚&

…

𝑇& 𝑂&,𝑚& Super-symbol: ⟨𝑇" 𝑂",𝑚" ,𝑛",𝑇& 𝑂&,𝑚& ,𝑛&⟩ 𝑇" 𝑂

",𝑚"

𝑢

Requirement: find the proper < N1,l1 > and < N2,l2 > to compose super-symbols for each required dimming level.

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• 2. Increase System Throughput

How to find < N1,l1 > and < N2,l2 >?

❼ Step 1: Collect available symbols 0.2 0.4 0.6 0.8 1

Dimming level of the LED

0.5 1 1.5 2 2.5

Symbol Error Rate (SER)

10-3 upper bound N=10 N=30 N=50

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• 2. Increase System Throughput

How to find < N1,l1 > and < N2,l2 >?

❼ 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 >?

❼ Step 3: Obtain the optimal combination via multiplexing and slope-based selection.

0.5 0.55 0.6 0.65 0.7

Dimming level of the LED

0.7 0.75 0.8 0.85 0.88

Normalized data rate

N = 10 N = 11 N = 12 N = 13 N = 14 N = 15 N = 16 N = 17 N = 18 N = 19 N = 20 N = 21

without multiplexing AMPPM (with multiplexing)

S(21,0.571) S(21,0.524)

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Basic Requirements

❼ Smart lighting: fine-grained dimming levels

SOLVED by multiplexing

❼ VLC: optimized throughput

SOLVED by AMPPM

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Recap

LED light Intensity 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 SmartVLC

Design Implementation

3 Evaluation 4 Conclusion

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• 3. Implementation

Available platforms

❼ High-end: USRP (≈ 5000✩), WARP (4900✩) ❼ Low-end: Arduino (≈20 e), BeagleBone Black (BBB, ≈65 e), Raspberry Pi (≈40 e)

BBB is selected in this project

❼ PRUs (similar to micro-controllers): BBB has two 200 MHz, 32-bit PRUs.

Used for sampling and operating LEDs.

Data Bridge

ARM PRU

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• 3. Implementation

Diagram of the front-end Transmitter and Receiver

Photodiode BBB MOSFET LED Power Ambient light Transmitter Photodiode Amplifier ADC BBB Receiver

Snapshot of the prototype Transmitter Receiver

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Next Subsection

1 Motivation 2 SmartVLC

Design Implementation

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 5

Distance (m)

20 40 60 80 100 120

Throughput (Kbps)

dimming level=0.18 dimming level=0.5 dimming level=0.7

Observations

❼ Reliable communication within 3.6 meters ❼ 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

10 20 30 40 50 60 70

Time (second)

50 60 70 80 90 100 110

Throughput (Kbps)

Ambient light: weak → strong

Observations

❼ 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 0.9

Dimming level of the LED

20 40 60 80 100 120

Throughput (Kbps)

AMPPM OOK-CT MPPM

Observations

❼ AMPPM outperforms OOK-CT (increases the throughput by 40% on average) ❼ 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 SmartVLC 25/26

Looking for PhD position!

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