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Visible Light Communications Professor Z. Ghassemlooy Professor Z. Ghassemlooy Optical Communications Research Group School of Computing, Engineering and Information Sciences Northumbria University United Kingdom

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SLIDE 1

Visible Light Communications

Professor Z. Ghassemlooy

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Professor Z. Ghassemlooy

Optical Communications Research Group School of Computing, Engineering and Information Sciences Northumbria University United Kingdom http://soe.northumbria.ac.uk/ocr/

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 2

Presentation Outline

  • Visible Light Communications
  • Light Sources

– Light Emitting Diode – Organic Light Emitting Diode

2

– Organic Light Emitting Diode

  • Equalisation
  • Results
  • Summary

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 3

What is the Problem? Radio Spectrum Famine

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  • Smart phones - we used them to:
  • Stream YouTube, Facebook videos
  • watch TV
  • download and store music and movies
  • photos
  • books
  • games
  • and sometimes talk to each other
  • Consume radio bandwidth
  • We are already feeling the pinch

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 4

What is the Problem? Network Power Usage

Wireless Access Wireless Access Fixed Access Fixed Access

(W) (W)

10 10 100 100

Wireless Access Fixed Access

(W)

10 100 Bell Labs Analysis

  • Wireless (RF) data is a rapidly

growing problem:

  • 10% per year improvement in

wire line equip. efficiency (Moore’s law).

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Metro Edge Metro Edge Core Core

Power /user (W Power /user (W

0.1 0.1 2010 2010 0.01 0.01 1 2015 2015 2020 2020

Metro Edge Core

Power /user (W

0.1 2010 0.01 1 2015 2020 law).

  • Assumes 9% per year

improvement in wireless (RF) access.

  • Wireless RF access power could

grow by a factor of 100 in 10 years.

  • By 2020 wireless RF access power

consumption dominates network.

  • M. Kavehrad,, The Pennsylvania State University, USA

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 5

xDSL

  • Copper based (limited bandwidth) - Phone and data combine
  • Availability, quality and data rate depend on service provider

RF

  • Spectrum congestion (license needed to reduce interference)
  • Security worries (encryption?)
  • Lower bandwidth than optical bandwidth
  • At higher frequencies atmospheric conditions attenuation

(rain) /absorption (oxygen gas) limits link to ~1km

frequency bands: 7, 18, 23, 35, 60, 66 GHz

Access Network Technology

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(rain) /absorption (oxygen gas) limits link to ~1km Cable

  • Shared network resulting in quality and security issues
  • Low data rate during peak times

FTTH

Satellite  Expensive

  • Limited bandwidth

OWC

  • 100 Mb/s, but Costly
  • Right of way required - time consuming

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 6

Access Network Technology - FTTH

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Fibre reaches further into Europe with over 2 million subscribers by 2010

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SLIDE 7

Access Network Technology – Radio

  • ver Fibre

core network feeder fibre distribution fibres (4-12 fibres) WiMAX UWB LTE femtocell ONT core network feeder fibre distribution fibres (4-12 fibres) WiMAX UWB LTE femtocell ONT

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

OLT network feeder fibre (4-12 fibres) FDH SSMF ONT 3PLAY distribution OLT network feeder fibre (4-12 fibres) FDH SSMF ONT 3PLAY distribution

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SLIDE 8

What is the Solution? Transmission by Light

  • Unregulated bandwidth (>540 THz), when

and where needed.

  • Over the last 20 years deployment of

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

  • Over the last 20 years deployment of
  • ptical fibre cables in the backbone and

metro networks have made huge bandwidth readily available to within

  • ne

mile

  • f

businesses/home in most places. But, HUGE BANDWIDTH IS STILL NOT AVAILABLE TO THE END USERS.

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SLIDE 9

Optical Wireless Communications

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Sunlight reflection

Source: Discovery Channel

Flame

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 10

OWC - Transmission Windows

Pave)amb-light >> Pave)signal (Typically 30 dB with no optical filtering)

er/unit wavelength

0.6 0.8 1 1.2

Sun Fluorescent Incandescent

Above 1400 nm - almost completely absorbed by the eye cornea Below 1400 nm: focused onto the retina, power levels must be limited for

10

IR UV

Wavelength (m) Normalised power

0.2 0.4 0.6 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

1st window IR 2nd window IR

must be limited for eye safety

VLC

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 11

Wireless – Technology and Standards

10 Gbps 1 Gbps

Fibre width MM wave communications

100 Gbps

Optical

FSO10G (WDM)

100 Mbps 10 Mbps 1 Mbps 200 m 50 m 500 m 1 km 5 km 15 km+

Microwave FSO

DSL Copper Cable

Link Range Bandw

Bluetooth WiMAX Optical WLAN

Analog FSO system Visible LED

Zig Bee EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 12

Visible LED

(bps) 50 M 100 M 400 M UWB 802.11a UFIR

Wireless – Technology and Standards

Visible LED

1 2 3 6 10 50 Distance (m) Data rate (b 115k 4 M 16 M Bluetooth ZigBee 802.11b 802.11a VFIR FIR SIR

http://www.ieee802.org/15/pub/TG7.html

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 13

Visible Light Communications

  • Features
  • Energy efficiency
  • Secured data communications
  • Secured data communications
  • No electromagnetic interference
  • Beam radiation directivity
  • Green communications
  • Added Value: Communications

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 14

2003 The Visible Light Communications Consortium (VLCC) – Japan 2008 “hOME Gigabit Access” (OMEGA) Project – EU - Develop global standards for home

VLC- When Did It All Start?

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

Develop global standards for home networking (infrared and VLC technologies). 2009 IEEE802.15.7 - Call for Contributions on IEEE802.15.7 VLC. 2011 Organic VLC – Northumbria University

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SLIDE 15

VLC Applications

 Airport & Station

  • Information for departure and arrival
  • signalling among, lighting infrastructure,

ground vehicles and aircraft  Store Arcade

  • Advertisement, electrical coupon

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 Signboard for illumination

  • Active advertisement, Menu

 Signal Lamp & Mobile

  • Transportation information

 Cafe/Home/Office

  • Internet, Home A/V network

 Aircraft & Hospital

  • Non-RF communication, Video

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 16

OW Apps: Broadband VLC

Indoor broadband broadcasting in Hospital / Supermarket / University / Office

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Source: Boston University

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 17
  • Established in 2003 by Japanese companies
  • Aims to standardize VLC Technology
  • Two standards proposed

– JEITA CP-1221

  • VLC systems (380 – 750 nm)
  • Range accuracy of 1 nm

VLC: Consortium (1/2)

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

  • Range accuracy of 1 nm
  • Subcarrier modulation
  • Range 1: 15 kHz- 40 kHz – Data communications
  • Range 2: 40 kHz – 1 MHz – Fluorescent light cannot use this

range, too slow and generate too much noise

  • Range 3: > 1 MHz – only for data transmission with special LEDs

Japan Electronics and Information Technology Industries Association

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SLIDE 18

VLC: Consortium (2/2)

  • Two standards proposed

– JEITA CP-1222 – VL ID systems

  • Subcarrier frequency: 28.8 kHz
  • Transmission rate: 4.8 kbps
  • Modulation: SC-4PPM

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

  • Modulation: SC-4PPM
  • Cyclic redundancy checks (CRC) for error

detection/correction

  • IEEE 802.15, Task Group 7 – Physical and media access

layer

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SLIDE 19

VLC: Technology

  • Every kind of light source could be used
  • LEDs are the preferred option
  • Up to 40 Mbps - Phosphorus LEDs can achieve up to 40 Mbps
  • Up to 100 Mbps - RGB LEDs
  • Up to 500 Mbps – Resonant cavity LEDs

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

  • Up to 500 Mbps – Resonant cavity LEDs
  • Use Bragg reflector (serving as a mirrors) to enhance the

emitted light

  • Offer spectral purity compared to conventional LEDs
  • Are energy efficient
  • Receivers:
  • Photodiodes
  • CCD and CMOS sensors
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SLIDE 20

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
  • Many Universities: Boston (USA), Oxford, Edinburgh,

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  • Many Universities: Boston (USA), Oxford, Edinburgh,

Northumbria, Keio (JP), Wonkwang & Chosun (SK), H H

  • Inst. (GER) + others
  • Siemens
  • France Telecom
  • EU COST Action 1101 (2011 – 2015) – more than 20

countries

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 21

General Lighting Sources

  • Incandescent bulb

– First industrial light source – 5% light, 95% heat – Few thousand hours of life

  • Fluorescent lamp

– White light – 25% light

5%

25%

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– Lifetime ~10,000s hours

  • Solid-state light emitting diode (LED)

– Compact – 50% light – More than 50,000 hours lifespan

  • Organic light emitting diode (OLED)

50%

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 22

Organic LED – State of the Art

  • Invented by Kodak in the 1980s
  • Intended for use in screens (brighter, thinner, faster, lighter and less

power consumption than LCDs)

  • Produced in large panels that illuminate a broad area.
  • Can be flexible with the relevant plastic substrate (create different shape)
  • 100% internal quantum efficiency (Fraunhofer IPMS – COMEDD, 2012)
  • Brightness 2.000 cd/m², 5mm thickness (Verbatim Velve, 2012)

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  • Brightness 2.000 cd/m², 5mm thickness (Verbatim Velve, 2012)
  • 120 lumen (~table lamp) (Philip Lumiblade GL350, 2012)
  • 80 lumen/watt with 20.000 hours of lifetime (LG, 2012)

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 23

Organic LED – Applications

High end smartphone display products: Super- AMOLED) (Samsung Galaxy S3 phone, 2012) 55 inch OLED HDTV (Samsung Electronics, 2012)

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

None of the commercial applications is for communications!

6 inch E-paper on plastic (XGA, 14 gram, 0.7mm thickness), (LG, 2012) Solar OLED car (BASF, 2012) Flexible AMOLED display (Samsung patent, 2012)

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SLIDE 24

Device Structure - OLED

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New technology, expensive and short life time. It is, however, has high potentials

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 25

Device Frequency Response

  • 6
  • 4
  • 2
  • nse (dB)

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200 400 600 800 1000

  • 12
  • 10
  • 8
  • 6

Frequency (kHz) Respon

Measured frequency response of (Philips) Luxeon-star white LED Measured frequency response of (Philips) Lumiblade white OLED

But OLED modulation bandwidth is much smaller than LED, due to the device size

How to improve the OLED bandwidth?

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria ~3 MHz ~17 MHz ~160 kHz

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SLIDE 26

OLED - Electrical Characterisation

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Source: Lumiblade, Korea Institute of Industrial Technology

For lighting Large panel  better for illumination  larger capacitance For communications Larger capacitor value  slow response

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 27

OLED – Bandwidth Improvement

  • Bandwidth equalisation (Analogue)
  • Digital filtering
  • Complex modulation

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

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SLIDE 28

OLED – Bandwidth Improvement

(5)

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

Therefore the received optical signal The DC gain (Lambertain)

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SLIDE 29

OLED – 1st Order Equalisation

The external capacitor Ceq

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

capacitor Ceq minimises the effect of OLED capacitance

  • H. Le-Minh, D. C. O'Brien, G. Faulkner, L. Zeng, K. Lee, D. Jung and Y. Oh, "100-Mbit/s NRZ Visible Light Communications Using a Post-Equalized White

LED", IEEE Photonics Technology Letters, vol. 21, no. 15, pp. 1063-1065, 2009

eq eqC

R T 

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SLIDE 30

OLED – 1st Order Equalisation

Parameter Value OLED half angle ϕhp 36o Angle of irradiance 0o Drive current (600 lux for illumination) 80 mA

Table 1 Simulation Parameters

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

Angle of acceptance 0o Half angle field of view of the receiver 85o Transmission distance 5 cm Optical power 1 W PIN responsivity 0.2 A/W

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SLIDE 31

OLED – 1st Order Equalisation

Map of frequency response corresponding to different equalisers

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

Philip Lumiblade OLED ~£70

  • H. Le Minh, Z. Ghassemlooy, A. Burton, P. A. Haigh, and S.-K. Liaw, "Bandwidth Improvement for Organic Light Emitting Diodes Based Visible Light

Communications", IEEE Communications Letters, 2012 (submited)

  • H. Le Minh, Z. Ghassemlooy, A. Burton and P. A. Haigh, "Equalization for Organic Light Emitting Diodes in Visible Light Communications" IEEE

GLOBECOM, Workshop on Optical Wireless Communications in Houston, USA, 5-9 December, 2011

The equalized bandwidth is maximum when Ceq~1.5 nF over the wide range value of Req.

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SLIDE 32

OLED – 1st Order Equalisation

  • 4
  • 2

B)

0.01 0.02 0.03

Impulse response before equalisation OLED frequency response before/after equalisation

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200 400 600 800 1000

  • 12
  • 10
  • 8
  • 6
  • 4

Frequency (kHz) Response (dB) unequalised Eq1 (390 Ohm, 15nF) Eq2 (820 Ohm, 3.9nF)

5 10 15 20 25

  • 0.01

Time (us)

  • 0.5

0.5 1 1.5 2 4 6 8 x 10

  • 3

Time (us)

Impulse response after equalisation

Equalised bandwidth can be increased up to 6 times Loss due to equalisation is ~ 8.5 dB

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austria

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SLIDE 33

OLED – 1st Order Equalisation

Measurement condition:

  • Data NRZ PRBS, 2^10

– 1

  • OLED DC current

80mA

  • Link distance 5cm (at

BER performance

33

IEEE GLOBECOM 2011, Houston, USA, 05/12/2011

  • Link distance 5cm (at

that point the luminous level is 600 lux (standard for office illumination)

  • PIN PD, 15cm2 +

AD8015 TIA

  • Electrical bandwidth

0.8xDataRate

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SLIDE 34

OLED – 1st Order Equalisation Baseline wander

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

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SLIDE 35

OLED – Decision Feedback Equalization

  • Widely used in digital systems transmitting through BW-limited AWGN channels
  • Better performance than ZF and MMSE-based filter

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

sampled incoming signal μT is the μth sample of the bit period, T. The number of filter taps is given by n and τ is the oversampling rate typically τ ≥ T/2; we selected τ = T/2 for this test. cn and bn are the adjustable coefficients

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SLIDE 36

OLED – DFE

Parameter Value Data format OOK-NRZ PRBS length 2^10 - 1

Unequalised and baseline-wandered RC equaliser’s BER performance

Measured BER vs. Bandwidth at different illumination level (lux)

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

PRBS length 2^10 - 1 Number of feed- forward taps 18 Number of feed- back taps 9 Algorithm Least Mean Square (LMS) Algorithm step size 0.03

DFE’s BER performance

  • A. Burton, P. A. Haigh, H. Le Minh, Z. Ghassemlooy, S. Rajbhandari and S. K. Liaw, "A Comparative Investigation Study of Modulation and Equalization

Techniques for White-Light Emitting Organic Light Emitting Diodes Using in Visible Light Communications", IEEE Communications Magazine, 2012 (submitted)

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SLIDE 37

OLED – Complex Modulation

Multiple carrier modulation: Orthogonal Frequency Division Multiplexing

  • Carriers are orthogonal to each others
  • Each carrier is modulated by QAM, PSK etc.

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

  • Each carrier is modulated by QAM, PSK etc.
  • Equalisation in small band of modulation bandwidth is

feasible

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SLIDE 38

Discrete Multi-Tone Modulation

  • The subcarriers used must fulfill the orthogonality

condition, such that:

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where Tsym is the time domain DMT symbol time and the complex exponential frequency domain data is given by N is the number of subcarriers and k is the subcarrier under inspection.

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

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SLIDE 39

OLED + DMT – Experimental

  • M = 16 QAM
  • Number of useful subcarriers = 64

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

  • The distance over which the symbols are transmitted is set appropriately to fix the

luminance level to 440 lux (for office environment)

  • A simple one-tap frequency domain equalizer
  • A. Burton, P. A. Haigh, H. Le Minh, Z. Ghassemlooy, S. Rajbhandari and S. K. Liaw, "A Comparative Investigation Study of Modulation and Equalization

Techniques for White-Light Emitting Organic Light Emitting Diodes Using in Visible Light Communications", IEEE Communications Magazine, 2012 (submitted)

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SLIDE 40

OLED + DMT- Received Constellations

5 Mbps 3 Mbps

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

  • To improve the equalizer and achieve higher bit rates, a longer pilot

symbol should be transmitted to provide a better representation of the memoryless channel.

  • Since the noise is additive and Gaussian, the transmission of an

abundance of pilot symbols would reduce the effect of noise by simple averaging.

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SLIDE 41

OLED + DMT- BER

Forward error correction limit

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

Recoverable

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SLIDE 42

OLED - Challenges

  • OLED is under development, therefore challenges
  • Materials and device structures
  • Heavily calibrated for display purpose (unlike LED used for

signalling and illumination)

  • Expensive (~10/20 times costlier than the same performing LED)
  • Lack of a wide range of commercially available products

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  • Communications aspects
  • Light efficiency is low  large illumination panels are typically

fabricated  high capacitance thus limiting the device modulation bandwidth (100’s kHz)

  • Limited researches in data communications
  • Not yet being standardised

IEEE GLOBECOM 2011, Houston, USA, 05/12/2011

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SLIDE 43

OLED – Possibilities & Potential

  • Possibilities and Future Work
  • Higher data rate - 0-15 Mbit/s for standard 10BASE-T Ethernet

communications

  • Working with the manufacturers to improve the device response

time (newer display has faster response and wider dynamic contrast range)

  • Device modelling and characterisation to optimise the performance

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EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

  • Device modelling and characterisation to optimise the performance
  • Possible to adopt the existing VLC standard (IEEE 802.15/16)
  • FEC inclusion
  • Potentials and Opportunity
  • OLED is available in many displays, tablets and phones  new

areas of short-range and personal VLC applications and researches

  • Toward mobile and flexible VLC
  • Environmental friendly  potentially to be adopted in wide range of

VLC

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SLIDE 44

Acknowledgment

  • OCRG’s OLED / VLC team, Northumbria

University

  • EURASIP
  • Prof. Erich Leitgeb - TU Graz

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  • Prof. Erich Leitgeb - TU Graz
  • EU Cost Action IC 1101

EURASIP Lecture Series, 11 May 2012, TUG, Graz, Austeria

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SLIDE 45

3rd Colloquium on Optical Wireless

Thank you!

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3rd Colloquium on Optical Wireless Communications @ 8th IEEE IET International Symposium on Communication Systems, Networks and DSP 18 – 20 July 2012 Poznan, POLAND

IEEE GLOBECOM 2011, Houston, USA, 05/12/2011