This document provides an overview of Li-Fi (Light Fidelity) technology. It discusses the history of using light for data transmission. It also describes how Li-Fi works by transmitting data using variations in light intensity that are undetectable to the human eye. The document outlines some of the main challenges in Li-Fi construction, such as loss of signal and blockages. It surveys recent research focused on addressing these challenges through techniques like OFDM, MIMO, and multiple access schemes.

1. LI-FI: LIGHT FIDELITY- A
SURVEY
PRESENTED BY: SHIHA MOHAN

2. OUTLINE
Introduction
History of Li-Fi
Present Scenario
Radio Spectrum
Why VLC?
Working Process
Challenges in Construction
Conclusion
References

3. Introduction
What is Li-Fi ?
Light-Fidelity
LI-FI is transmission of data through illumination, sending
data through a LED light bulb that varies intensity faster
than human eye can follow.

4. Introduction

5. History of Li-Fi
The 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 Haas
University of Edinburgh.

6. Li-Fi

7. 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

8. Radio Spectrum
Issues regarding Radio Spectrum

9. Electromagnetic Spectrum

10. Why VLC ?
Radio
Waves
Infrared
Rays
Visible
Rays
Ultraviolet
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 ?

12. Li-Fi
Light - Fidelity

13. 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 .

14. How Li-Fi Works ?

15. 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 .

16. 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.

17. 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

18. 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.

19. VLC Modulation Techniques with User
Satisfaction
Intensity Modulation – Loss of amplitude and phase
information
User Satisfaction –
• Dimming
• Illumination

20. • Dimming- by controlling the drive current
• Analog Dimming
• Digital Dimming
• PPM, VPPM, PWM, MPWM, MPPM

21. Three VLC Modulation methods for Multi-colored
LED:
• Color Intensity Modulation (CIM)
• Color Shift Keying (CSK)
• Metameric Modulation (MM)

22. OFDM IN VLC
OFDM techniques developed :
• Direct Current (DC) biased OOFDM (DCO-OFDM)
• Asymmetrically Clipped OOFDM (ACO-OFDM)
• Asymmetrically Clipped DC biased OFDM (ADO-
OFDM)

23. MIMO IN VLC
To achieve high data rate
Non-imaging MIMO – depends on symmetry of
receiver, inconsistent
Imaging MIMO – Light spatial diversity
• To mitigate ICI and system complexity – Optical
Spatial Modulation (OSM)

24. 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 bandwidth
Optical Code Division Multiple Access (OCDMA) –
Balanced incomplete block designs code (BIBD)
Optical beamforming system model

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

26. OPTICAL BEAMFORMING SYSTEM MODEL

27. CONCLUSION
Outlined 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.

28. 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/

29.  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.
 Jungnickel, V., Pohl, V., Noenning, S., & von Helmolt, C. (2002). A physical model
for the wireless infrared communication channel. IEEE Journal on Selected Areas
in Communications, 20(3), 631–640.
 Fath, T., & Haas, H. (2013). Performance comparison of MIMO techniques for
optical wireless communications in indoor environments. IEEE Transactions on
Communication, 61(2), 733–742.
 Wilkins, A., Veitch, J., & Lehman, B. (2010). LED lighting flicker and potential
health concerns: IEEE standard PAR1789 update. In Proceedings of IEEE energy
conversations congress expo, Atlanta, GA, USA (pp. 171–178).
 Dyble, M., Narendran, N., Bierman, A., & Klein, T. (2005). Impact of dimming
white LEDs: Chromaticity shifts due to different dimming methods. In Proceedings
of SPIE, 5941, 59411H1–9.
 Audeh, M., & Kahn, J. (1994). Performance evaluation of L-pulse-position
modulation on non-directed indoor infrared channels. In Proceedings of IEEE
international conference on communication, Vol. 4. New Orleans, LA, USA, pp.
660–664.

30.  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.
 Suh, Y., Ahn, C. H., & Kwon, J. K. (2013). Dual-codeword allocation scheme for
dimmable visible light communications. IEEE Photonics Technology Letters,
25(13), 1274–1277.
 Lee, S. H., & Kwon, J. K. (2012). Turbo code-based error correction scheme for
dimmable visible light communication systems. IEEE Photonics Technology Letters,
24(17), 1463–1465.
 Kim, J., & Park, H. (2014). A coding scheme for visible light communication with
wide dimming range. IEEE Photonics Technology Letters, 26(5), 465–468.
 Wang, T. Q., Sekercioglu, Y. A., & Armstrong, J. (2013). Analysis of an optical
wireless receiver using a hemispherical lens with application in MIMO visible light
communications. Journal of Lightwave Technology, 31(11), 1744–1754.