Visible Light Communication - Tutorial -

Visible Light Communication

- Tutorial -

Visible Light Communication

- Tutorial -

2008. 03. 172008. 03. 17

Samsung ElectronicsSamsung Electronics

802.15 DCN: 15-08-0114-00-0000

2/29802.15 DCN: 15-08-0114-00-0000

Storyline(Tutorial on Visible light communication)

VLC introductionIdentity : Definition, Differentiation from other standardsHistory : VLC related activities in historyMotivation : LED infra, No regulation, No interference, Security…

LED introductionLED technical evolutionLED market evolutionLED applications/advantagesLED modulation characteristics (B+Y, RGB, RCLED)

VLC potential applicationVLC applicable services (Indoor, ITS, NFC) VLC categorization (I2M, M2M, M2F)VLC killer application

Indoor LBS High-speed video streaming

VLC demo Demo map PI, IB, VL (including movie)

SummaryTechnical issues (Oxford)

Source, Channel, ReceiverLink simulationLink ExperimentSystem resultTechnical challenge

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Outline

Part 1 (Samsung)

VLC introduction

LED introduction

VLC potential application

Part 2 (Oxford univ.)

VLC components

Technical challenges

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VLC introduction

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 and electronic devices

Unregulated : no room to use more radio frequency

Using in the restricted area : aircraft, spaceship, hospital

Eye safety

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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 KiteIn Battle

VLC history

VLCVLC

6/29

Information delivery through reflection by mirror (Heliograph)

The use of fire or lamp

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

Traffic light : signal discrimination by color (Walk/Stop)

Morsecode

VLC history – Low speed

7/29

Bell’s Photophone (1880)

• Optical source : sunlight

• Externally modulation by vibrating mirror

• Receiver : parabolic mirror with crystalline selenium cells

• 700 ft (213m) sound transmission

VLC history - Photophone

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

http://www.freespaceoptic.com/

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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 : contribution 15-07-0623-01, AT&T Labs discussed the Terahertz spectrum band which covers 300 GHz to 10 THz. • This mmWave WPAN will operate in the new and clear band including 57-64 GHz unlicensed band • The millimeter-wave WPAN will allow high coexistence (close physical spacing) with all other microwave systems in the 802.15 family of WPANs

Frequency band for VLC

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Data

rate

(bps)

115K

4M

100M

480M

16M

50M

UFIR

FIR

IR

VIR

VLC

HDR UWBHDR UWB

1 113

Distance (m)

2 6 20 50

UWBUWB

802.11a802.11a

802.11b802.11b

BluetoothBluetooth

ZigBeeZigBee

VLC Characteristic

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VLC Characteristic

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-LOS

Interference

LOS

Security

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

(mW/Mbps)

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VLC vs. RF Characteristic

Property VLC RF

Bandwidth Unlimited, 400nm~700nm Regulatory, BW Limited

EMI No High

Line of Sight Yes No

Standard IG-VLC Yes

Hazard NoYes (H2O reaction to

2.4GHz)

Mobile

To

Mobile

Visibility (Security) Yes No

Power Consumption Relative low Medium

Distance Short Medium

Power Budget Tight Medium

Infra

to

Mobile

Security Yes No

Infra LED Illumination Access Point

Mobility Limited Yes

Coverage (Distance) Short (~10m)Wide (Short ~ Long Range)

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VLC motivation

Communication community trendUbiquitous (Connect each other everywhere, every time)

Security

LED trendLED technology (efficiency, brightness)

LED Cost

Environmental trendHealth

Energy saving

Intrinsic characteristic of VLCVisibility

No interference / No regulation

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Outline

Part 1 (Samsung)

VLC introduction

LED introduction



VLC components


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LED technical evolution

Source: Credit Suisse, 2006.11.2Brightness / Power ratio

Co

st /

Bri

gh

tne

ss r

atio

Incandescent Lamp

Halogen Lamp

HID (High-Intensity Discharge)

Fluorescent Lamp

LED

LED

LED

LED

Performance and Price comparison

2003

2005

2010

2015

50 100 1500

1

10

100

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Air PollutionsUNFCCC (United Nations Framework Convention on Climate Change), Kyoto Protocol to the UNFCCC

(Dec. 1997)Decreasing CO2(10 k ton/year, 2002 at Korea)

Waste Materials & Environmental HazardsRoHS (Restriction of the use of Certain Hazardous Substance): 1, July 2006.

Pb, Hg, Cd, Cr6+, Polybrominated biphenyls(PBB), Polybrominated diphenyl eters(PBDE)

WEEE (Electrical and Electronic Equipment ) Producer Responsibility

Energy saving effectElectricity at Korea

278 TWh(2002), 7.2 % of USA20% for Lighting:55.6 TWh50% saving by LED:27.8TWhEnergy Saving Effect:

3 Nuclear Stations (1GW/day) 2 B$/year

Source: KOPTI (The Korea Photonics Technology Institute)

LED driver

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LED Market Forecast

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

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LED application

Economicalefficiency

Back LightingBack Lighting Mobile PhoneMobile Phone

Home applicationsHome applications

digital devicedigital device

TFT LCD TV TFT LCD TV

General General LightingLighting

CommunicatCommunicationion

DisplayDisplay

General Lighting General Lighting

Task LightingTask Lighting

Signal LampSignal Lamp

VLCVLC

Mobile to MobileMobile to Mobile

Infra to MobileInfra to Mobile

Exterior, interior Exterior, interior

displaydisplay

Sign & Sign & Architecture Architecture

displaydisplay

LED screenLED screen

LED Applications

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LED modulation characteristics

R+G+B LEDB + Phosphor LED RCLED

~40 Mb/s ~100 Mb/s ~500 Mb/s

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Outline

Part 1 (Samsung)

VLC introduction

LED introduction



VLC components


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VLC application

BandwidthBandwidthSecuritySecurity

CoverageMobility

IRIRU

VU

V

780nm

380nm

1nm

100μm

RF

RF

3cm

1m

visi

ble

visi

ble

PeripheralInterface

LAN

BankingBanking Door LockDoor Lock In PlaneIn PlaneDigital Digital

HospitalHospital

ITS (Navigation)ITS (Navigation)SAMSUNG

Sign BoardSign Boarde-booke-book

VisibleLAN

RFProhibited

InformationBroadcast

SecuritySecurity

E-display

Contents Contents MachineMachine

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Indoor applicationIndoor application

Mobile-to-MobileMobile-to-Fixed

LED Illumination Infrastructure

Mobile-to-InfraFixed-to-Infra

Ubiquitous

Security

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Requirements (Indoor application)Requirements (Indoor application)

Mobile to Mobile Mobile to Fixed Mobile to Infra Fixed to Infra

Link Bi-direction Bi-direction Bi or Uni Bi or Uni

Reach ~1m ~1m ~3m ~3m

Rate ~100M ~100M ~10M ~10M

Application Contents sharing File transfer

Video streaming

M-commerce

Indoor navigation

LBS

Networked robot

Data broadcast

Alternative IrDA, Bluetooth, UWB

IrDA, Bluetooth, UWB

WLAN

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Outdoor applicationOutdoor application

Vehicle-to-Vehicle

Traffic control Infrastructure

Vehicle-to-Infra

Outdoor advertising

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VLC application evolutionVLC application evolution

LED penetration

MobileDisplay

SignITS

Illumination

100MIndoor

10MIndoor

10MOutdoor

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Indoor navigation schemeIndoor navigation scheme

Uni-direction Bi-direction Hybrid Hot spot

Link

Rate Down : ~10k Down : ~10M

Up : ~100M

Down : ~10k

Up : ~10M

Down(light) : ~10k

Down(HS) : ~100M

Infra Lighting with optical ID

Lighting with optical ID

Receiver

In-building network

Routing server


RF access point

In-building network

Routing server


Hot spot

Mobile Receiver

Large storage

Map info

Routing software

Receiver

Transmitter

Receiver

RF connectivity

Receiver

Large storage

Routing software

Other service

LBS

Ad-hoc connection

LBS

Rx TRx Rx Rx

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High-speed High-speed high-security connectivity connectivity

What You See Is What You Send(WYSIWYS)

E-Contents Vending Machine

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Mobile to Mobile

(100Mbps,Samsung)

Music broadcasting

(6Mbps, Oxford Univ.)

Tx, Rx

(~30Mbps,Oxford Univ.)

Infra to Mobile

(10Mbps, Tamura Inc.)Infra to Mobile(VLAN)

(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 system

(100kbps, Hongkong Univ.)

Demonstrations

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VLC demonstrationVLC demonstration

100 Mb/s, 1mBidirection

20 Mb/s, 3mUnidirection

4 Mb/s, 3mBidirection

Mobile to mobile Infra to mobileInfra to mobile

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Mobile-to-mobile demo

PDA/UMPC

Spot @ 30 cm

What You See Is What You Send (WYSIWYS)

120 Mb/s, 1m, Full duplex

File transfer and video streaming

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Mobile-to-mobile (protocol)

D LSTS

Standby Transmitting

Beam guiding User alignmentDevice discovery Start steaming Temporal blocking

( < 8 sec.)Streaming end

D LS D LSTS D LSTS

SecondaryScreen

PrimaryScreen

Link

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Mobile-to-mobile (Link performance)

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 Mb/s 240 Mb/s

20 40 60 80 100 120-10

-5

0

5

10

0

2

4

6

8

10

Distance (cm)

320 Mb/s -log(BER)

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RGB WDM transmission

20 Mb/s, 3m, Uni-direction

Information broadcast from sign board

Infra-to-mobile demo

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

Data Rate = 10 Mb/s

Power Meter

-11

-10

-9

-8

-7

-6

-5

-4

0 1 2 3 4 5 6

REDBLUEGREENRED+BLUERED+GREENBLUE+GREENWHITESAMSUNG

Data Rate = 20 Mb/s

Infra-to-mobile (Link performance)

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TDMA-based P2MP

4 Mb/s, 3 m, bi-direction

Secure indoor LAN

Infra-to-mobile

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Downstream : White LED

Upstream : LD

Infra-to-mobile (Link performance)

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Summary (Part 1)

VLC introductionIdentityVLC historyMotivation

LED introductionLED technical evolutionLED market forecastLED applicationLED modulation characteristics

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

Mobile-to-mobile Infra-to-mobile

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Part 1 (Samsung)

VLC introduction

LED introduction



VLC components


802.15 DCN: 15-08-0114-00-0000

Visible Light Communications

Dominic O’Brien, University of Oxford,

[email protected]

Contributions from Communications Group at Oxford

802.15 DCN: 15-08-0114-00-0000

Overview

> Visible Light Communications> Transmitter> Channel> Receiver

> Technical challenges> Higher bandwidth> Enabling mobility and reliability

> Conclusions

802.15 DCN: 15-08-0114-00-0000

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

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LED Modulation

> Opto-electronic response

Page 5

0 10 20 30 40 50-25

-20

-15

-10

-5

0

freq ( MHz)

Rel

ativ

e re

spon

se (

dB)

White response

Blue response

Measured LED small-signal bandwidth

sR dVL

sC

dC

V

I

Luxeon LED

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

SPICE Model

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Improvement of LED response

> Using blue-response only (blue filtering)

Page 10

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

(no

rmal

ised

)

~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

802.15 DCN: 15-08-0114-00-0000

Improvement of channel response

> Receiver equalisation

Page 11

Fitting falling time curve

Equalization

Measured LED impulse response

Improved LED transmission BW

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Improvement of LED bandwidth

> Pre-equalization: Resonant driving circuit

Page 12

0 10 20 30 40 50-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency ( MHz)

Res

pons

e no

rmal

ised

to m

axim

um(

dB)

C=2200pF white1000pF white680pF white330pF white68pF white

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

0 10 20 30 40 50 60

Bandwidth (MHz)

Tra

nsm

issi

on

(d

B)

A single resonant driving circuit

Multiple resonant points (normalized)

Bandwidth of 16 LED source

802.15 DCN: 15-08-0114-00-0000

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

Page 6

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VLC modelling

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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

802.15 DCN: 15-08-0114-00-0000

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

802.15 DCN: 15-08-0114-00-0000

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

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Optical receiver: constant radiance theorem

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

i

Ai

Ao

Aii<=Ao

Aii<=Ao

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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

2

P

ARFOM b

Detector Area A

Receiver sensitivity Pmin

Field of view 2Sr

Bit rate Rb

802.15 DCN: 15-08-0114-00-0000

Typical link: components

Page 22

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

2Rillum = 3 m

LLOS = 2 mReceiver

• Concentration lens

D = 50mm

F = 60mm

• Detection area

35 mm2

• Pre-Amp

• Post-Amp

(ampl. limiting)

Range

L = 2 m

Rillum = 1.5 m

Rcomm = 0.5 m

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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

Page 23

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

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Bandwidth improvement: post equalisation

> Pre- and post-equalization: single LED link

Pre-equalisation: experiment

Post-equalisation: simulation

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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)

Illuminating Source

Beamsplitter

ReceiverRetroreflectingTransceiver showing angle of rotation

Reader

Tag

Illuminating Source

Beamsplitter


Illuminating Source

Beamsplitter


Reader

Tag

802.15 DCN: 15-08-0114-00-0000

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

802.15 DCN: 15-08-0114-00-0000

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

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Retro-reflecting link demonstration system

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

Tag ReaderTag Reader

Demonstration system

802.15 DCN: 15-08-0114-00-0000

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

802.15 DCN: 15-08-0114-00-0000

MIMO VLC: simulation Model

Transmitting process

Receiving process

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MIMO VLC: simulation system

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MIMO VLC: preliminary Results

Page 31

Position of the receiverAggregate data rate is linearly proportional to the

number of channels and channel rate

802.15 DCN: 15-08-0114-00-0000

Future technical challenges

> Data rate> Equalisation> MIMO> Complex modulation

> Integration in infrastructure> Uplink

>Retro-reflecting link> RF/VLC integration

802.15 DCN: 15-08-0114-00-0000

Conclusions

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

>Challenges>Integration with Wireless infrastructure>Higher performance

Documents

Visible Light Communication - Tutorial -