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March 2008 doc.: IEEE 802.15-<08/0114-01>

Submission

Project: IEEE P802.15 Working Group for Wireless Personal Area NProject: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)etworks (WPANs)Submission Title: [Visible Light Communication : Tutorial]Date Submitted: [9 March 2008]Source: [(1)Eun Tae Won, Dongjae Shin, D.K. Jung, Y.J. Oh, Taehan Bae, Hyuk-Choon Kwon, Chihong Cho, Jaeseung Son, (2) Dominic O’Brien (3)Tae-Gyu Kang] Company [(1)Samsung Electronics Co.,LTD, (2)University of Oxford, (3)ETRI]Address [(1)Dong Suwon P.O. Box 105, 416 Maetan-3dong, Yeongtong-gu, Suwon-si, Gyeonggi-do, 443-742 Korea, (2) Wellington Square, Oxford, OX1 2JD, United Kingdom, (3) 161 Gajeong-dong, Yuseong-gu, Daejeon, 305-700, Korea]Voice:[(1)82-31-279-5613,(3)82-42-860-5232], FAX: [(1)82-31-279-5130], E-Mail:[(1)[email protected], (2) [email protected], (3)[email protected]]Re: []

Abstract: [The overview of the visible light communication (VLC), application scenarios and demonstrations in the various are presented in this document. The research issues, which should be discussed in the near future, also are presented.]

Purpose: [Tutorial to IEEE 802.15]Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

Visible Light Communication

- Tutorial -

Visible Light Communication

- Tutorial -

2008. 03. 172008. 03. 17

Samsung Electronics

University of Oxford

ETRI

Samsung Electronics

University of Oxford

ETRI

2/64

Part 1 (Samsung)

VLC introduction

LED introduction

VLC potential application

Part 2 (Oxford Univ.)

VLC components

Technical challenges

Outline

3/64

VLC (Visible Light Communication)

: New communication technology using “Visible Light”.

Visible Light

: Wavelength between ~400nm (750THz) and ~700nm (428THz)

General Characteristic

Visibility : Aesthetically pleasing

Security : What You See Is What You Send.

Health : Harmless for human body

Unregulated : no regulation in optical frequency

Using in the restricted area : aircraft, spaceship, hospital

Eye safety

VLC introduction

4/64

1900s Current405 B.C. 1800s280 B.C. 1880~

FireFire

SunlightSunlight

LampLamp

LEDLED

Heliograph

Beacon

Fire

Pharos

Lighthouse

Ship-to-ship

Comm.

Photophone

By Bell

Traffic Light

/Signboard Light

800 B.C.

Burning Kite

In Battle

VLCVLC

VLC history

5/64

Information delivery using mirror reflection (Heliograph)

The use of fire or lamp

• Beacon fire, lighthouse, ship-to-ship comm. by Morse code

Traffic light : R/G/B color multiplexing (Walk/Stop)

Morsecode

VLC history - Low speed

6/64

Bell’s Photophone (1880)

• Optical source : sunlight

• Modulation : vibrating mirror

• Receiver : parabolic mirror

• Distance : 700 ft (213m)

Excerpted from: The New Idea Self-Instructor edited by Ferdinand Ellsworth Cary, A. M. (Monarch Book Company, Chicago & Philadelphia, 1904)

http://www.freespaceoptic.com/

VLC history - Photophone

7/64

Low Frequency(Long wavelength)

CoverageMobility

visibleIR UV

700nm 400nm100μm

RF

3cm1m 1nm

428THz 750THz3THz10GHz300MHz 300PHz

High Frequency(Short wavelength)

BandwidthSecurity

1mm

300GHz

IrDA

802.15.3c

IG-THz

IG-VLC802.11802.16

• IG-THz : 300 GHz to 10 THz (contribution 15-07-0623-01) • 802.15.3c : 57 GHz to 64 GHz• IrDA : 334THz(900nm) to 353THz (850nm)

Frequency band for VLC

8/64

VLC CharacteristicsData

rate

(bps)

115K

4M

100M

480M

16M

50M

UFIR

VFIR

FIR

VLC

1 113

Distance (m)

2 6 20 50

UWB

802.11a

802.11b

Bluetooth

ZigBee

FIR

SIR

9/64

1Mb/s, 1m

100Distance × Speed (m × Mb/s)

10

100

Power consumption

Speed

1000

50 Mb/s, 50m

500 Mb/s, 3m

4 Mb/s, 1m

10

1 SAMSUNGSAMSUNG

Non-LOSInterference

LOSSecurity

Directivity + SimplicityDirectivity + Simplicity Optical connectivity saves powerOptical connectivity saves power

(mW/Mbps)

VLC Characteristics

10/64

MaturedBeginning (IG-VLC)Standard

Coverage

Mobility

Infra

Visibility (Security)

Distance

Power Consumption

Visibility (Security)

WideNarrow

YesLimited

Access PointLED Illumination

NoYes

Infra to

Mobile

MediumShort

MediumRelative low

NoYesMobileTo

Mobile

YesNoHazard

NoYesLine of SightHighNoEMI

Regulatory, BW LimitedUnlimited, 400nm~700nmBandwidth

RFVLCProperty

VLC vs. RF Characteristics

11/64

Communication community trendUbiquitous (Connected anywhere, anytime)

Security

LED trendLED technical evolution (efficiency, brightness)

LED illumination infra

Environmental trendEnergy saving

No E-smog

Intrinsic characteristic of VLCVisibility

No interference / No regulation

VLC motivation

12/64

Part 1 (Samsung)

VLC introduction

LED introduction



VLC components


Outline

13/64

Source: Credit Suisse, 2006.11.2Brightness / Power ratio

Cos

t / B

right

ness

ratio

IncandescentLamp

HalogenLamp

HID (High-Intensity Discharge)

Fluorescent Lamp

LED

LED

LED

LED

Performance and Price comparison

2003

2005

2010

2015

50 100 1500

1

10

100

LED technical evolution

14/64

Environment protection

Kyoto Protocol : CO2 emission regulation

RoHS : Hg-free bulb

WEEE : Producer responsibility

Energy saving

Electricity in Korea

278 TWh(2002), 7.2 % of USA

20% for Lighting : 55.6 TWh

50% saving by LED : 27.8TWh

Energy Saving Effect:

3 Nuclear Stations (1GW/day)

2 B$/year

Source: KOPTI (The Korea Photonics Technology Institute)RoHS : Restriction of the use of Certain Hazardous SubstanceWEEE : Waste Electrical and Electronic Equipment

LED driver (environmental perspective)

15/64

LED

DRAM

NAND

NAND, DRAMLED ※CAGR :15%

Source: Deutsche Bank, 2007. 22002 2010 2006 2006

29.2 billion $

12.4 billion $

2017

LED

LED

6.3 billion $

11billion $

29 billion $

LED market comparison with NAND, DRAM

LED Market Forecast

16/64

Economicalefficiency

DisplayDisplay

Mobile deviceMobile device

LCD BLULCD BLU

LED displayLED display

IlluminationIllumination

OthersOthersITSITS

General Lighting General Lighting

Office LightingOffice Lighting

Street LightingStreet Lighting

Head/tail lightHead/tail light

Traffic signalTraffic signal

LED Applications

MedicalMedical

CommunicationCommunication

LED application

17/64

R+G+B LEDB + Phosphor LED RCLED

~40 Mbps ~100 Mbps ~500 Mbps

LED modulation characteristics

18/64

Part 1 (Samsung)

VLC introduction

LED introduction



VLC components


Outline

19/64

BandwidthBandwidthSecuritySecurity

CoverageMobility

IRIRU

VUV

780nm

380nm

1nm

100μm

RFRF

3cm

1m

visi

ble

visi

ble

PeripheralInterface

LAN

BankingBanking Door LockDoor Lock In PlaneIn PlaneDigital Digital

HospitalHospital

ITS (Navigation)ITS (Navigation)SAMSUNG

Sign BoardSign Boardee--bookbook

VisibleLAN

RFProhibited

InformationBroadcast

SecuritySecurity

E-display

Contents Contents MachineMachine

VLC application

20/64

Mobile-to-MobileMobile-to-Fixed

LED Illumination Infrastructure

Mobile-to-InfraFixed-to-Infra

Ubiquitous

Security

Indoor application

21/64

Bi or UniBi or UniBi-directionBi-directionLink

WLANIrDA, Bluetooth, UWB

IrDA, Bluetooth, UWB

Alternative

Data broadcastIndoor navigationLBSNetworked robot

File transferVideo streamingM-commerce

Contents sharingApplication

~10Mbps~10Mbps~100Mbps~100MbpsRate

~3m~3m~1m~1mReach

Fixed to InfraMobile to InfraMobile to FixedMobile to Mobile

Requirements (Indoor application)

22/64

Vehicle-to-Vehicle

Traffic control Infrastructure

Vehicle-to-Infra

Outdoor advertising

Outdoor application

23/64

LED penetration

MobileDisplay

SignITS

Illumination

100MbpsIndoor

10MbpsIndoor

10MbpsOutdoor

VLC application evolution

24/64

Down(light) : ~10kbpsDown(HS) : ~100Mbps

Down : ~10kbpsUp : ~10Mbps

Down : ~10MbpsUp : ~100Mbps

Down : ~10kbpsRate

Link

LBS

ReceiverRF connectivity

Lighting with optical ID

RF access pointIn-building networkRouting server

Hybrid

ReceiverLarge storageRouting software

ReceiverTransmitter

ReceiverLarge storageMap infoRouting software

Mobile

LBSAd-hoc connection

Other service


Hot spot


ReceiverIn-building networkRouting server


Infra

Hot spotBi-directionUni-direction

Rx TRx Rx Rx

Indoor navigation scheme

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What You See Is What You Send(WYSIWYS)

E-Contents Vending Machine

High-speed high-security connectivity

26/64

Mobile to Mobile(100Mbps,Samsung)

Music broadcasting(6Mbps, Oxford Univ.)

Tx, Rx(~30Mbps,Oxford Univ.)

Infra to Mobile(10Mbps, Tamura Inc.)

Infra to Mobile (LAN)(4Mbps, Samsung)

Infra to Mobile, VLCC (Keio Univ., NEC, Toshiba, Sony, Matsushita, Casio etc. )(4.8kbps, illuminations, visible light ID, sign board, applications based on JEITA)

Sign board(10Mbps, Samsung)

LowLowspeedspeed

HighHighspeedspeed

LED array(~1Gbps, Keio Univ.)

Audio transmission(100kbps, Hongkong

Univ.)

Demonstrations

27/64

100 Mbps, 1mBidirection

20 Mbps, 3mUnidirection

4 Mbps, 3mBidirection

Mobile to mobile Infra to mobileInfra to mobile

VLC Demonstrations

28/64

PDA/UMPC

Spot @ 30 cm

What You See Is What You Send (WYSIWYS)

120 Mbps, 1m, Full duplex

File transfer and video streaming

Mobile-to-mobile demo

29/64

D LS TS

Standby Transmitting

Beam guiding User alignmentDevice discovery

Start steaming Temporal blocking( < 8 sec.)

Streaming end

D LS D LS TS D LSTS

SecondaryScreen

PrimaryScreen

Link

Mobile-to-mobile (protocol)

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20 40 60 80 100 120-10

-5

0

5

10

Distance (cm)20 40 60 80 100 120

-10

-5

0

5

10

Distance (cm)

Cov

erag

e (c

m)

120 Mbps 240 Mbps

20 40 60 80 100 120-10

-5

0

5

10

0246810

Distance (cm)

320 Mbps

-log(BER)

Mobile-to-mobile (Link performance)

31/64

RGB WDM transmission

20 Mbps, 3m, Uni-direction

Information broadcast from sign board

Infra-to-mobile demo

32/64

Transmitter (RGB Sign-Board) Receiver (Silicon PD)

Data Rate = 10 Mbps

Power Meter

-11

-10

-9

-8

-7

-6

-5

-4

0 1 2 3 4 5 6

RED

BLUE

GREEN

RED+BLUE

RED+GREEN

BLUE+GREEN

WHITE

SAMSUNG

Data Rate = 20 Mbps

Infra-to-mobile (Link performance)

33/64

Infra-to-mobile

TDMA-based P2MP

4 Mbps, 3 m, bi-direction

Secure indoor LAN

34/64

Downstream : White LED Upstream : LD

Infra-to-mobile (Link performance)

35/64

VLC introductionVLC historyMotivation

LED introductionLED technical evolutionLED market forecastLED applicationLED modulation characteristics

VLC potential applicationApplication categoryIndoor : Navigation, High-speed connectivityOutdoor : ITS, AdvertisingDemonstration

Demonstration overviewMobile-to-mobileInfra-to-mobile

Summary (Part 1)

36/64

Part 1 (Samsung)

VLC introduction

LED introduction



VLC components


Outline

37/64

Visible Light Communications

Dominic O’Brien, University of Oxford,

[email protected]

Contributions from Communications Group at Oxford

38/64

Overview

> Visible Light Communications> Transmitter> Channel> Receiver

> Technical challenges> Higher bandwidth> Enabling mobility and reliability

> Conclusions

39/64

VLC Sources

> Blue LED & Phosphor> Low cost> Phosphor limits bandwidth> Modulation can cause colour

shift

> RGB triplet> Higher cost> Potentially higher bandwidth> Potential for WDM> Modulation without colour

shift

Single chip LED spectrum RGB LED spectrum

40/64

LED Modulation

> Opto-electronic response

0 10 20 30 40 50-25

-20

-15

-10

-5

0

freq (MHz)

Rela

tive response (

dB

)

White response

Blue response

Measured LED small-signal bandwidth

sR dVL

sC

dC

V

I

Luxeon LED

Rs = 0.9727 ΩL = 33.342 nHCs = 2.8 nFCd = 2.567 nFtt = 1.09 ns

SPICE Model

41/64

Improvement of LED response

> Using blue-response only (blue filtering)

350 400 450 500 550 600 650 700 750 8000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Wavelength(nm)

Inte

nsity (

norm

alis

ed)

~130 ns

~25 ns

Measured optical spectrum Measured impulse response

> Issue: Only 10% of signal power is recovered⇒ Reducing SNR, link distance

> LEDs with more blue energy [1] could be used to gain more filtered power, however the balance of white colour is shifted

Blue filtering

[1] Grubor, J., et al., "Wireless high-speed data transmission with phosphorescent white-light LEDs", Proc. ECOC 07 (PDS 3.6), pp. 1-2. ECO [06.11], 16-20 Sep. 2007, Berlin, Germany

42/64

Improvement of channel response

> Receiver equalisation

Fitting falling time curve

Equalization

Measured LED impulse response

Improved LED transmission BW

43/64

Improvement of LED bandwidth> Pre-equalization: Resonant driving circuit

DC arm of Bias Tee

3.3342e-008HHigh-speed buffer

Resonant capacitor

Network Analyser

DC bias current from Laser driver

Luxeon LED

0 10 20 30 40 50-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency (MHz)

Response n

orm

alis

ed to m

axim

um

(dB

)

C=2200pF white

1000pF white

680pF white

330pF white

68pF white

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

00 10 20 30 40 50 60

Bandwidth (MHz)

Tran

smis

sion

(dB

)

A single resonant driving circuit

Multiple resonant points (normalized)

Bandwidth of 16 LED source

44/64

Channel modelling> Two propagation paths:> Line of sight (LOS): strong paths calculated using the illumination patterns

from LED arrays> Diffuse: modelled by assuming the room is equivalent to an integrating

sphere> Channel impulse response is calculated for each point in the room

45/64

VLC modelling

46/64

Room Power Distribution

> Assume > 1% modulation of

typical illumination power

> Typical receiver performance

> Conclusions> Very high SNR

available> SNRmin =

38.50dB> SNRmax =

49.41dB> Modulation limited

by source bandwidth

47/64

Noise sources

> Optical noise> Daylight

> Generates DC photocurrent> Blocked at receiver due to AC coupling > Creates shot noise

> Other optical sources> Fluorescent, Incandescent

> Creates electrical interference photocurrent harmonics

> Mitigated by> Optical filtering

> Wavelength is in band of desired signal> Electrical filtering

48/64

Optical receiver

> Receiver consists of> Optical filter

> Rejects ‘out-of-band’ ambient illumination noise

> Lens system or concentrator> Collects and focuses radiation

> Photodetector (or array of detectors)> Converts optical power to photocurrent

> Incoherent detection> Preamplifier (or number of preamplifiers)

> Determines system noise performance> Post-amplifier and subsequent processing

Optical filter

Optical system

Photodetector

Amplifier

Output

Input radiation

49/64

Optical receiver: constant radiance theorem

> Optical ‘gain’ of receiver limited by required field of view

Ωi

Ωο

Ai

Ao

AiΩi<=AoΩο

AiΩi<=Ao2π

50/64

Receiver performance: figure of merit

> Receiver Figure of Merit (FOM)> Fibre systems

> Performance determined by sensitivity (given sufficient detector area)

> FOV usually not relevant> Free space systems

> Etendue crucial determinant

min

2P

ARFOM bπ=

Detector Area A

Receiver sensitivity

Pmin

Field of view 2π Sr

Bit rate Rb

51/64

Typical link: components

Transmitter

•16 Luxeon LEDs

• PILLUM = 1.5W

• LED pitch = 60 mm

• IDC = 220 mA

• Mod-index = 0.1

• 45o wide-beam lens

• 7 resonant freq.

• Flat BW of 25 MHz

Transmitter and receiver specifications

2×Rillum = 3 m

LLOS = 2 mReceiver• Concentration lens

D = 50mmF = 60mm

• Detection area35 mm2

• Pre-Amp• Post-Amp

(ampl. limiting)

RangeL = 2 mRillum = 1.5 mRcomm = 0.5 m

52/64

Typical link: illumination

Power distribution in receiving plane

-20

-25

-30

-35

-40

-25

x coordinate(m)

y co

ordi

nate

(m)

Received power in dBm/cm2

0.5 1 1.5 2 2.5 3 3.5 4

0.5

1

1.5

2

2.5

3

3.5

4

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30 35 40 45 5010-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

Data rate (Mbit/s)

BE

R

L = 2mL = 2.5m

Typical link: BER performance

Eye diagram

30 Mb/s

40 Mb/s

50 Mb/s

• System test in normal lighting condition (room filled with other high-power white light sources) • Longer distance ⇒ SNR penalty (BER)

NRZ

Flat BW ⇒ baseline wandering reduction

54/64

Bandwidth improvement: post equalisation

> Pre- and post-equalization: single LED link

Pre-equalisation: experiment

Post-equalisation: simulation

55/64

Retro-reflecting link

> Novel optical communications between reader and tag> Low power (tag has no source)> Long range (determined by illumination source )> Visibly secure (user can see beam of light)

θIlluminating Source

Beamsplitter

ReceiverRetroreflectingTransceiver showing angle of rotation

Reader

Tag


Beamsplitter



Beamsplitter


Reader

Tag

56/64

Retro-reflecting link: retro-reflectors

> Front surface reflector array on rigid plastic substrate> Metallised front face> Normal incidence reflection loss of 5.5dB (relative to

theoretical maximum)> Returns a polarisation state close to incident for all

angles of incidence

Schematic of retro-reflecting surface Photograph of surface

57/64

Retro-reflecting link demonstration system

Rx

Decode

2400bits/s data

Data 2400bits/s

Rx

LED TX

SLM Tx

2400 bits/s reader to tag2400 bits/s tag to reader

Data code

Data retime

Memory

PIC

Data codeMemory

PIC

Terminal program

Terminal program

58/64

Retro-reflecting link demonstration system

> Demonstrator> 2.4kb/s bi-directional communication over several metres

Tag ReaderTag ReaderDemonstration system

59/64

Future developments: optical MIMO

> RF MIMO> Scattering provides invertible H matrix and decorrelation

(capacity gain)> Difficult to shape radiation pattern with small antenna> Optical MIMO> No decorrelation> Invertible H matrix achieved by system and geometry

design> Simple low-cost elements (lenses) can provide high

directivity and/or complex beamshaping

60/64

MIMO VLC: simulation Model

Transmitting process

Receiving process

61/64

MIMO VLC: simulation system

62/64

MIMO VLC: preliminary Results

Position of the receiverAggregate data rate is linearly proportional to the

number of channels and channel rate

63/64

Future technical challenges

> Data rate> Equalisation> MIMO> Complex modulation

> Integration in infrastructure> Uplink

>Retro-reflecting link> RF/VLC integration

64/64

Conclusions

>VLC offers>High SNR channel>Intuitive alignment>Visibly secure channel

>Challenges>Integration with Wireless infrastructure>Higher performance

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