LIFI: Light Fidelity - A Survey

LI-FI: LIGHT FIDELITY- A SURVEY

PRESENTED BY: SHIHA MOHAN

OUTLINE

IntroductionHistory of Li-FiPresent ScenarioRadio SpectrumWhy VLC?Working ProcessChallenges in ConstructionConclusion

References

IntroductionWhat is Li-Fi ?

Light-FidelityLI-FI is transmission of data through illumination, sending

data through a LED light bulb that varies intensity faster than human eye can follow.

Introduction

History of Li-FiThe technology truly began during the 1990's in countries like

Germany, Korea, and Japan where they discovered LED's could be retrofitted to send information.  Harald Haas continues to wow the world with the potential to use light for communication .

Prof. Harald HaasUniversity of Edinburgh.

Li-Fi

Present Scenario Radio Spectrum is congested but the demand for wireless data

double each year .Every thing, it seems want to use wireless data but the capacity is drying up.

1.4 Million Base Stations 5 Billion

Radio SpectrumIssues regarding Radio Spectrum

Electromagnetic Spectrum

Why VLC ?Radio

Waves

Infrared Rays

Visible Ray

s

Ultraviol

et Rays

X- Rays

Gama

Rays

Gama rays cant be used as they could be dangerous.

X-rays have similar health issues.

Ultraviolet light is good for place without people, but other wise dangerous for the human body.

Infrared, due to eye safety regulation, can only be used with low power.

HENCE WE LEFT WITH THE ONLY THE VISIBLE - LIGHT SPECTRUM.

Why only VLC ?

WHO CAN REPLACERADIO WAVES FOR

WIRELESSCOMMUNICATION ?

Li-Fi

Light - Fidelity

Working Process If the led is on, you transmit a digital 1, if its off you transmit a 0. The LEDs

can be switched on and off very quickly, which gives nice opportunities for

transmitting data. Hence all that us required is some LEDs and a controller

that code data into those LEDs. We have to just vary the rate at which the

LED’s . Flicker depending upon the data we want to encode . Thus every light source will works as a hub for data transmission .

How Li-Fi Works ?

How Li-Fi Works ?

On one end all the data on the internet will be streamed to a lamp driver when the led is turned on the microchip converts the digital data in form of light .

A light sensitive device (photo detector) receives the signal and converts it back into original data. This method of using rapid pulses of light to transmit information wirelessly is technically referred as Visible Light Communication .

Challenges in Construction

Loss of amplitude and phase.Flicker and color variation.Strong correlation of optical channels.Hard to achieve receive diversity.Hard to provide optical uplink services.Blockage of objects and shadowing.Limited coverage within opaque space.

In this study, it summarizes the state of art technologies to overcome the challenges.• Indoor optical wireless channel model

• VLC modulation with user satisfaction

• OFDM in VLC

• MIMO in VLC

• Multiple access and resource allocation

Indoor Optical Wireless Channel Model

θi = Irradiance angle w.r.t transmitter axis Ψi = Incidence angle w.r.t receiver angle

Ψmax = Field of View semi-angle of the receiver

θmax = Source radiation semi-angle

If optical detectors are symmetric

to the transmitter LED, VLC channels

remain highly correlated.

VLC Modulation Techniques with User Satisfaction

Intensity Modulation – Loss of amplitude and phase information

User Satisfaction –

• Dimming

• Illumination

• Dimming- by controlling the drive current

• Analog Dimming

• Digital Dimming

• PPM, VPPM, PWM, MPWM, MPPM

Three VLC Modulation methods for Multi-colored LED:

• Color Intensity Modulation (CIM)

• Color Shift Keying (CSK)

• Metameric Modulation (MM)

OFDM IN VLCOFDM techniques developed :

• Direct Current (DC) biased OOFDM (DCO-OFDM)

• Asymmetrically Clipped OOFDM (ACO-OFDM)

• Asymmetrically Clipped DC biased OFDM (ADO-OFDM)

MIMO IN VLCTo achieve high data rateNon-imaging MIMO – depends on symmetry of

receiver, inconsistentImaging MIMO – Light spatial diversity

• To mitigate ICI and system complexity – Optical Spatial Modulation (OSM)

MULTIPLE ACCESS AND RESOURCE ALLOCATION

Three user access schemes

• Distance-Prior (DP) – access nearest LED

• Service Aggregation (SA) – multiple LED serve one user

• Bandwidth-based (BB) – LED affordable bandwidthOptical Code Division Multiple Access (OCDMA) –

Balanced incomplete block designs code (BIBD)Optical beamforming system model

(A) SYMBOL GENERATION FOR CODED-MEPPM USING THE (1100100000000) OOC CODEWORD AND A (13,4,1)- BIBD

(B) THE RESULTING SYMBOL

OPTICAL BEAMFORMING SYSTEM MODEL

CONCLUSIONOutlined the state of the art research on Li-Fi

network.The concept of Li-Fi is currently attracting a great

deal of interest, not least because it may offer a genuine and efficient alternative to radio-based wireless.

As a growing number of people and their devices access wireless internet, the air waves are becoming increasingly clogged, making it more and more difficult to get a reliable, high-speed signal.

REFERENCES

 Xu Bao, Jisheng Dai, Xiarong Zhu. (Aug. 2015). Impact Factor: 0.96 · DOI: 10.1007/s11276-015-0889-0

Rahul R Sharma et al , Int.J.Computer Technology & Applications, Vol 5 (1),150-154 

National Telecommunications and Information Admission (NTIA). (2003). FCC frequency allocation chart. Available http://www.Ntia. doc.gov/osmhome/allochrt  

Kavehrad, M. (2010). Sustainable energy-efficient wireless applications using light. IEEE Communications Magazine, 48(12), 66–73.  

Visible Light Communications Consortium. http://www.vlcc.net/  

Home Gigabit Access (OMEGA). http://www.ict-omega.eu/  

IEEE 802.15 WPAN Task Group 7 (TG7) Visible Light Communication. http://www.ieee802.org/15/pub/TG7.html  

Li-Fi Consortium. http://www.lificonsortium.org/  

OBrien, D., Minh, H. L., Zeng, L., Faulkner, G., Lee, K., Jung, D., et al. (2008). Indoor visible light communications: Challenges and prospects. Proceedings of SPIE Free-Space Laser Communications VIII, 7091, 1–9.

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Doshi, M., & Zane, R. (2010). Control of solid-state lamps using a multiphase pulsewidth modulation technique. IEEE Transactions on Power Electronics, 25(7), 1894–1904. 15. Lee, K., & Park, H. (2011). Modulations for visible light communications with dimming control. IEEE Photonics Technology Letters, 23(16), 1136–1138.

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