LiFi

HISTORY

• GrahamBell(1880) -Photophone

• Carl Zeiss Jena developed light speaking device.

• Invention of Lasers revolutionized free sapce optics in 1960.

• Gfeller (1978) – Wireless communication using optical spectrum

• Nakagawa laboratory (2003)- Transmission with LeDs.

• VLCC establishment in 2003• Jan 2010 : researchers from Siemens and

Fraunhofer Institute of Telecomm. demonstrated transmission at 500mbps

• December 2010 : St. Cloud Minnesota• July 2011 : live demonstration was presented

VLC

●COMPARISON OVER IR●COMPARISON OVER RF

●WHY LIFI?

Infrared CommunicationInfrared:• Used in devices such as notebook

computers, television remote controls and even some newer mobile phones

• Infrared Data Association (IrDA) has standardized over 30 specifications

VLC over IR• Narrow beam of VLC over IR

– Less opportunity for eavesdropping– Decrease in adjacent device

interference– beam blocked from illuminating more

than one device at once.

• Installation– Easier and cost effective

• Obstruction – VLC : Less obstruction– LOS component dominates thus effect of multipath is small

• Signal-to-noise ratio (SNR) – High SNR obtainable in VLC as a consequence of the illumination

requirements.

• Power Efficiency– VLC eliminates severe power efficiency loss

• Safety– IR causes potential visual safety problems

OVER RFRADIO FREQUENCY

– Wide usage in WLAN networks– Compromise information, interfere with

sensitive equipment

VLC over RF• Health Concerns – RF : radiation damage– VLC : no health concerns, no safety

regulations

• Carbon-dioxide footprint– VLC : Significantly reduced due to its

low energy consumption

• Radio wave interference– VLC : no interference with RF based systems exist

• Communication link– VLC: has better channel condition than Radio Frequency

(RF)

• Frequency allocation – VLC : Doesn’t have any frequency allocation issues

present in RF

• Bandwidth – VLC: Is not limited

• Visible Light Communication is not regulated

Why Li-Fi?

• Visible light LED will be used everywhere– The extensive use of LEDs render- an ideal

ubiquitous data transmitter

• Image sensors can be used as receivers– Accurate direction of incoming vector– Aids in applications where RF cannot be deployed

What is Li-Fi?

• Visible Light Communication through LEDs.

• Send data by flashing light at speeds-0s &1s

• Data rates upto 500Mbps

• Employs semiconductor devices containing a photodiode.

• Key aspect : Intensity modulation

• Termed as direct-detection

• Light Source – Optical Access Point

• Employs OFDM

Methods of VLC

METHOD I

METHOD II

Principles of communication using image sensor

WHITE LEDs• Long life span• High lighting efficacy and color

rendering index• Easy installation.• Low heat productivity. • Low maintenance cost• Energy saving• High safety• Start immediately. • No light pollution• Low light decay. • Green initiative. • Fast response

TECHNICAL ASPECTS OF THE SYSTEM DESIGN

Typical Block Diagram of a VLC system

Modulation/ Demodulation TechniquesOptical Carrier Schemes:

• Optical coherent receivers:– Detect the optical carrier phase.– Require a local oscillator, optical

mixer and optical filter.• LEDs emit incoherent light, signal

power is very less.• Viable modulation is intensity

modulation (IM).• Practical down-conversion technique is

direct detection (DD), much simpler to implement than coherent detection.

Electrical Modulation Techniques

• On-Off keying(OOK) , Pulse Position Modulation(PPM) – widely used in RF and IR communication

systems

– Multipath delay– Channel delay spread(ISI) – limits data

rate to 10Mbps– To overcome - additional receiver

complexity• Orthogonal Frequency Division

Multiplexing(OFDM)– Inherent robustness of OFDM against

multipath effects– Support high data rates without the

need for complex channel equalizers– Offers high bandwidth efficiency– Can easily combine with TDMA and

FDMA

OFDM

• Wireless data transmission technology

• Carrier centers are put on orthogonal frequencies

• ORTHOGONALITY - The peak of each signal coincides with trough of other signals

• Subcarriers are spaced by Δf=1/Ts• Total passband bandwidth will be B ≈ N·Δf (Hz)

Modulation

STANDARDIZATION EFFORTS• Visible Light Communications Consortium(VLCC) Purpose :

– To realize safe, ubiquitous telecommunication system using visible light through the activities of market research, promotion, and standardization.

• Two standards introduced by VLCC(2008): – To avoid fragmentation of proprietary protocols1. JEITA CP-1221 :

• Mainly used for transmitting information on identification and arbitrary data.

2. JEITA CP-1222 : • Differs from JEITA CP-1221 in that it is supposed to be only used

for communication purposes and is slightly more specific in its suggestions.

• IEEE standard - 802.15.7 (2011):– IEEE Standard for Local and Metropolitan Area

Networks– Was developed by Task Group 7 (TG7)– Proposes PHY/MAC Specification

Fig : IEEE 802.15.7 Standard Specification of MAC and PHY layers

Applications-Personal Area Communication

• Download of needed information for digital signage applications

IrDA and VLCC have been working together since Sept 2008 for a visible light communication using IrDA protocol stacks

• 100 Mbps Full-duplex multi-access VLC system

Implemented at Nakagawa Laboratory, JapanBased on 100 Mbps infrared LAN system (Standard proposed by

ICSA of ARIB)

• High-Speed Parallel Wireless VLC system using 2D Image Sensor and LED Transmitter

By Keio University and Sony Kihara Laboratory

• Communication using LED spotlight “Hikari Guide System” by Shimizu Corporation, Japan

• Visible light information broadcast system Prototype made by NEC and Matsushita Electric Works,

members of VLCC

• Application of VLC to ITS(Intelligent Transport System)

By VLCC and The Japan Traffic management Technology Asstn

• Information broadcast system using LED traffic lights

The Nippon Signal Co.Ltd and VLCC

• Multiple transmission using multiple colorsJoint project of Keio University and JVC

“Sound Spot”

Applications that enable users to know their locations in accuracy of several

meters• Global location service that uses VLC

Prototype made by NEC and Matushita Electric Works

• Flow planning survey system for a storeNakagawa laboratories , Inc

• Flow planning survey system for a store

Applications of location determination(in several millimeter accuracy)

• Three dimensional position measuring system using VLC

• Accurate position detection of a transmitter or a receiver

Applications that use augmented reality

• Augmented Reality of real world image added with personal info

• Lighthouse VLC

Applications where radio waves cannot be used

• Underwater VLCBy Rise, Nakagawa lab, Inc, Keio university, Oct 2010

LiFi Consortium• Non-profit organization devoted to introduce optical wireless

technology. • Charter members : a leading group of international technology

companies and research institutions in optical communication technology.

• Purposes:– Promote optical wireless communications up to the multi-

gigabit range– Inform potential implementers of the companies and resources

available to help them achieve their product goals– Create whole solutions in anticipation of customer needs– Coordinate with standardization groups and other industry

Wireless communication using visible light will change how we live, how we work, and how we communicate. It offers users virtually unlimited communication capability.

Being a ultra high-speed, high security, biologically friendly communications network it can allow the creation and expansion of seamless computing applications using very large bandwidth high-frequency pulsed light instead of radiowaves and microwaves. In the near future, this technology is predicted to revolutionize the commtn system being affordable and contention free. Thank you.