Vlc

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Visible Light Communication

Le Tien Anh - 80623864Nakagawa lab – Keio university

Advanced course in Digital Communications3rd July 2007

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Overview

1. Introduction

2. Technology

3. Applications

4. Conclusion

5. Question & Answer

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Characteristics

• What is VLC:– Stands for “Visible light communication”.– Communications of information using light that is visible to the

human eye.

• How is VLC:– Ubiquitous: Omni-presence.– Harmless for human body and electronic devices. Power has not

been limited.– The available visible light bandwidth is about 300THz (450-750

THz). It is considerably larger than the current available radio frequency bandwidth (about 300GHz)

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History

Radio waves

Microwave Infrared Ultra-Violet X-rays Gamma-rays

Visible light

Tribes used smoke, fire as

optical wireless communication

long ago

June 3, 1880, Alexander

Graham Bell transmitted the

first wireless telephone

message on "photophone”

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Difficulties

• Ambient interference: – Obstacles: Must obtain a LOS.– Interferences from other visible light sources

(sun, bulbs…)– Also suffer from the multi-path effect as light

reflects.

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Modulation schemes

• There are 4 popular baseband modulation schemes used in VLC:– Pulse Position Modulation (PPM):

• 2-PPM, 4-PPM.• I-PPM.

– Sub-carrier Pulse Position Modulation (SC-PPM):• SC-PPM.• SC-I-PPM.

– Sub-carrier Frequency Shift Keying (SC-FSK)– Sub-carrier Phase Shift Keying (SC-PSK)

• The main output uses OOK (on/off keying), one kind of Intensity Modulation-Direct Detection (IM-DD).

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Pulse Position Modulation (PPM)

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Adopted from: Ref [2]

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Sub-carrier Pulse Position Modulation (SC-PPM)

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Adopted from: Ref [2]

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SC-FSK/PSK

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Adopted from: Ref [2]

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Baseband modulation:PPM/I-PPM,

SC-PPM/SC-I-PPMSC-FSK/SC-PSK

Data Visible light modulation

Baseband demodulation:PPM/I-PPM,

SC-PPM/SC-I-PPMSC-FSK/SC-PSK

DataVisible light

demodulation

Limitations of the VLC technology Baseband modulationData RF modulation

Baseband demodulationData RF demodulation

BPF

BPF

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Applications

• Audio systems:– Silent concert

• Indoor:– VLC and PLC (power-line communication),– Smart super market,– Museum,– Hospital.

• Outdoor:– Intelligent Transport System

• Underwater

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Audio systems

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Indoor applications

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Adopted from Ref.[3]

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Outdoor applications

• ITS: Intelligent Transport System:– Pedestrians support:

• Roadside information terminal– Driver and passenger support:

• Toll collection,• Traffic information, road map…• Ground to train communications.

– Vehicles support:• Logistic.

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Conclusion

• VLC can lead to many interesting applications.

• No international standard or protocol has been developed.

• VLC still has to overcome many limitations both in the transmitter’s LED and in the receiver’s PD.

• “Best things in life are free”

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Questions and Answers

Thank you

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References

• [1]. M.Z.Afgani et.al. Visible light communication using OFDM. IEEE 2006.

• [2]. H.Sugiyama, S.Haruyama, M.Nakagawa. Experimental investigation of modulation method for visible-light communications.IEICE transection

• [3]. LED lamp http://en.wikipedia.org/wiki/Image:Ampoules.jpg

• [4]. NEC’s ITS

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