Vlc

Visible Light Communication Le Tien Anh - 80623864 Nakagawa lab – Keio university Advanced course in Digital Communications 3rd 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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Introduction Technology Applications Conclusion Referenceｓ Q&A

History Tribes used smoke, fire as optical wireless communication long ago

June 3, 1880, Alexander Graham Bell transmitted the first wireless telephone message on "photophone ”

Visible light

Radio waves

Microwave

Infrared

Ultra-Violet

X-rays

Gamma-rays

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Introduction Technology Applications Conclusion Referenceｓ Q&A

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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Introduction Technology Applications Conclusion Referenceｓ Q&A

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). 6

Introduction Technology Applications Conclusion Referenceｓ Q&A

Pulse Position Modulation (PPM)

Adopted from: Ref [2] 7

Introduction Technology Applications Conclusion Referenceｓ Q&A

Sub-carrier Pulse Position Modulation (SC-PPM)

Adopted from: Ref [2] 8

Introduction Technology Applications Conclusion Referenceｓ Q&A

SC-FSK/PSK

Adopted from: Ref [2] 9

Introduction Technology Applications Conclusion Referenceｓ Q&A

Limitations of the VLC technology Data

Baseband modulation

RF modulation

BPF

Data

Baseband demodulation

RF demodulation

BPF

Data

Baseband modulation : PPM/I-PPM, SC-PPM/SC-I-PPM SC-FSK/SC-PSK

Visible light modulation

Data

Baseband demodulation : PPM/I-PPM, SC-PPM/SC-I-PPM SC-FSK/SC-PSK

Visible light demodulation

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Introduction Technology Applications Conclusion Referenceｓ Q&A

Applications • Audio systems: – Silent concert

• Indoor: – – – –

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

• Outdoor: – Intelligent Transport System

• Underwater 11

Introduction Technology Applications Conclusion Referenceｓ Q&A

Audio systems

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Indoor applications

Adopted from Ref.[3] 13

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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. 14

Introduction Technology Applications Conclusion Referenceｓ Q&A

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” 15

Introduction Technology Applications Conclusion Referenceｓ Q&A

Questions and Answers Thank you

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Introduction Technology Applications Conclusion Referenceｓ Q&A

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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