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Visible Light Communications

Hoa Le Minh and Zabih Ghassemlooy

Optical Communications Research Group (OCRG)

School of Computing, Engineering and Information Sciences

Northumbria University, United Kingdom

hoa.le-minh@northumbria.ac.uk 

(ERASMUS Framework)

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Presentation Outline

• Optical wireless communications backgrounds

• Visible Light Communications

 – Light Sources

 – Current technologies

 – Challenges

• Organic Light Source

•

Summary

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Why Optical Wireless?

RF spectrum:

crowded, expensive

OW spectrum:

free, large bandwidth

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Optical Wireless Applications

(short range)

• Traffic Communications

• Public data broadcasting

•

Indoor broadband broadcasting in Hospital/ Supermarket / University / Office

• Home Access Networks

•

Military Communications

“Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011 

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 Applications

Beam reflection (directional)

Source: Discovery Channel

Flame

Probably the first ever applications in visible light communications

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OW Apps: Indoor Broadband

Source: Oxford University

(OMEGA project)

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 Apps: Traffic Communications

FSO

M Kavehrad

PSU, USA

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Research in VLC

• VLCC (Casio, NEC, Panasonic Electric Works,

Samsung, Sharp, Toshiba, NTT, Docomo)

• OMEGA (EU Framework 7)

•

IEEE 802.15 Wireless Personal Area Network standards• Boston University

• Siemens

• France Telecom

• Oxford University• Edinburgh University

• Northumbria University

“Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011 

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General Lighting Sources

• Incandescent bulb

 – First industrial light source

 – 5% light, 95% heat

 – Few thousand hours of life

• Fluorescent lamp

 – White light

 – 25% light

 – 10,000s hours

• Solid-state light emitting diode (LED) – Compact

 – 50% light

 – More than 50,000 hours lifespan

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Light Source Spectrum

IRUV

Wavelength (m)

   N  o  r  m  a   l   i  s  e   d  p  o  w  e  r   /  u  n   i   t  w  a  v  e   l  e  n  g   t   h

0

0.2

0.4

0.6

0.8

1

1.2

 0  . 3  

 0  .4  

 0  . 5  

 0  . 6  

 0  . 7  

 0  . 8  

 0  . 9  

1  . 0  

1  .1  

1  .2  

1  . 3  

1  .4  

1  . 5  

Sun

Fluorescent

Incandescent

“Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011 

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LED  – Fundamental

Light Emitting Diode (LED)

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White-Light LED

•

LED types:RGB Blue chip + Phosphor OLED

Well-known technology, limited

use, problem with balancing

each R, G, B component to

create white light

Popular for today general

lighting, efficient and cheap

New technology,

expensive and short life

time. It is, however, very

potential

“Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011 

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VLC Transceivers

Input

data signal

Modulators LED array

LPF

Pre-

amplifierPD

 LDC

 R

Concentrator

Optical receiver

Transmitter

Recovered

data signal

DC arm

Inductance (Lseries) High-speed

buffer  

Resonant

Capacitor (C ) 

DC bias currentfrom Laser driver  

Luxeon LED, R  Signal

Bias Tee  A

Z

Individual LED driving circuit

DC current: for illumination (provide sufficient brightness)

Signal: Data for communications

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Pre-Equalisation

DataLED

DCcurrent

source

Bias-

TeeC1 

R 1 

PIN

Oscilloscope

Amplifier

Concentrator

Blue

filterPre- Equalizer

C2  Beam-

shaping lens

R 2 

driver 1

driver 2

driver 3

White

light Blue

light

10 20 30 40 50 60 70 80 90 10010

-6

10-5

10-4

10-3

10-2

10-1

Data rate (Mbit/s)

       B       E       R

 

Blue-filtering

Pre-Equalization

• 45 MHz equalized bandwidth achieved

• 80 Mbit/s OOK-NRZ transmission

VLC link configuration

Equalization

BER performance

“Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011 

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Cellular VLC

Transmitter

Board with core

Indoor channel

receiver

d1

H

r1

r2

θa

φ 

receiver

- User is highly mobile

- Cellular structure and cell handover strategy are being developed

- Cell size and transmit power are optimised

-36

-34

-33-32

-30

-28

-28-28

-28

-28

-28-26

-26

-26

-26

-26

-26

-24

receiver plane coordinate(mm)

  r  e  c  e   i  v  e  r  p   l  a  n  e  c  o  o

  r   d   i  n  a   t  e   (  m  m   )

-1000 -500 0 500 1000

-1000

-500

0

500

1000

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MIMO VLC Channel Matrix

Tx1 Tx2 Tx3 Tx4

4 Rx

44434241

34333231

24232221

14131211

 H  H  H  H 

 H  H  H  H 

 H  H  H  H 

 H  H  H  H 

 H 

Issue:

If there is a geometry symmetry

rank(H ) < 4

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Thank you

“Gheorghe Asachi” Technical University of Iasi Iasi Romania 13/06/2011