The attached power point presentation mention the working principle, modulation methods used, advantages, disadvantages and applications of Li-Fi. The material will be useful for KTU final year B Tech students who prepare for the subject EC 405, Optical Communications.

1. 1
Light Fidelity
(Li-Fi)
MEC

2. 2
Contents
• Introduction.
• Li-Fi Working.
• Wi-Fi Limitations
• Li-Fi Advantages.
• Li-Fi Modulation Schemes.
• Li-Fi Applications.

3. 3
Li-Fi
• Professor Harald Haas, the Chair of
Mobile Communications at the University
of Edinburgh - founder of Li-Fi.
• Prof. Haas coined the term Li-Fi, co-
founder of pure LiFi.
• Li-Fi regarded as light-based Wi-Fi.
• Use of visible portion of electromagnetic
spectrum.
• Prof. Haas demonstrated a Li-Fi prototype
at TED Global conference, Edinburgh on
12th July 2011.

4. 4
Li-Fi
• Prof. Haas used a table lamp with an LED
bulb to transmit a video of a blooming
flower that was then projected onto a
screen.
• Haas periodically blocked light from the
lamp with his hand to show that the lamp
was indeed the source of video data.
• Li-Fi use transceivers fitted with LED
lamps that could light a room as well as
transmit and receive information.

5. 5
.

6. 6
Li-Fi Building Blocks

7. 7

8. 8
Wi-Fi Limitations
• Use of 2.4 – 5 GHz radio frequencies to
deliver wireless internet access.
• Bandwidth limited to 50-100 Mbps.
• Reliability drops with increase in the
number of Wi-Fi hotspots and volume of
Wi-Fi traffic.
• Security and speed concerns.
• Wi-Fi vulnerable to hackers, penetrates
easily through walls.

9. 9
Wi-Fi Challenges
 Capacity:
• Spectrum scarcity with the arrival of 3G,
4G and higher.
 Efficiency:
• Radio masts consume massive amounts
of energy, more energy needed for cooling
the station rather than transmission of
radio waves, station efficiency only 5%.

10. 10
Wi-Fi Challenges
 Availability:
• Radio waves cannot be used in all
environments, like in aircrafts, chemical
and power plants and in hospitals
 Security:
• Penetrates through walls, can be
intercepted.
 Latency:
• Of the order of ms.

11. 11
Li-Fi Scores
 Capacity:
• Visible light spectrum 10,000 times wider
than radio spectrum. Li-Fi has greater
bandwidth and readily available
equipments.
 Efficiency:
• LED lights consume less energy, highly
efficient.

12. 12
Li-Fi Scores
 Availability:
• Light sources easily available.
 Security:
• Light does not penetrate through walls.
• Data transmission more secure.
 Latency:
• Of the order of μs.
 Li-Fi modelled after protocols established
by IEEE 802 workgroup.

13. 13
Spectrum Usage

14. 14

15. 15

16. 16
“Li-Fi can achieve the same data rates as
USB cables which is challenging for wireless
technologies such as Bluetooth and Wi-Fi”.
- Frank Deicke, Head of Li-Fi development,
Fraunhofer Institute for Photonic Microsystems,
Dresden, Germany

17. 17
Li-Fi Working

18. 18

19. 19
Visible Light Communication
• Method of using rapid pulses of light to
transmit information wirelessly.
• Uses visible light between 400 THz (780
nm) and 800 THz (375 nm) as the optical
carrier for data transmission and for
illumination.
• Data rates of greater than 100 Mbps using
high speed LEDs with multiplexing.
• IEEE 802 workgroup defines physical
layer (PHY) & media access control (MAC)
layer for VLC/Li-Fi.

20. 20
Visible Light Communication
 MAC layer:
• supports 3 multi-access technologies:
peer-to-peer, star configuration and
broadcast mode.
• handles physical layer management
issues such as addressing, collision
avoidance and data acknowledgement
protocols.

21. 21
Li-Fi Modulation Schemes
• Physical layer divided into 3 types: PHY I,
II, III and employ a combination of different
modulation schemes.
• On-Off Keying.
• Variable Pulse Position Modulation.
• Colour Shift Keying.
• Sub-Carrier Inverse PPM.
• Frequency Shift Keying.
• Subcarrier Index Modulation OFDM.

22. 22
Visible Light Communication
• Parallel data transmission LED arrays.
• Each LED transmits a separate stream of
data, increase in VLC data rate.
• Lights to be kept on to transmit data, can
be dimmed that they are not visible to
humans but still be capable of transmitting
data.

23. 23
On-Off Keying
• Manchester coding - period of positive
pulses = period of negative pulses.
• Doubles the bandwidth required for
transmission.
• For higher bit rates, spectrally more
efficient run length limited (RLL) coding
used.
• Dimming supported by adding OOK
extension to adjust aggregate output to
the correct level.

24. 24
Variable Pulse Position Modulation
• Encode data using pulse position within a
set time period.
• Pulse duration long enough to allow
different positions to be identified.
• Allows pulse width to be controlled to
support light dimming.

25. 25
Colour Shift Keying
• Used if illumination system uses RGB-type
LEDs.
• Output data carried by the colour itself.
• Output intensity can be near constant.
• Mixing of RGB primary sources produces
different colours which are coded as
information bits.
• Transceiver complexity increased.

26. 26
Sub-Carrier Inverse PPM
• Sub-carrier part and DC part.
• When there is no requirement for lighting
or indicating, Sub-Carrier PPM used to
save energy.
• DC part used only for lighting or indicating.

27. 27
Frequency Shift Keying
• Data represented by varying the
frequencies of carrier signal.
• Two distinct values (0 and 1) using two
distinct frequencies.

28. 28
Sub-Carrier Index Modulation
OFDM
• Use of sub-carrier index to convey
information to the receiver.
• Adds additional dimension to conventional
2D amplitude/phase modulation (APM)
techniques such as QAM and ASK.

29. 29
Limitations
• Light cannot pass through objects, if the
receiver is blocked, signal will immediately
be cut out.
• Need to switch to radio waves if light
signal is blocked.
• Reliability and network coverage.
• Interference from external light sources
like sunlight, normal bulbs and opaque
materials in the transmission path.

30. 30
Limitations
• High installation costs.
• Can’t have a light bulb to provide data to a
high-speed moving object.
• Still need Wi-Fi in case of obstacles
(trees, walls, structures) along the light
path.

31. 31
Criticisms
• Cannot work in the dark or if it is raining or
foggy.
• Not built into modern computers.
• Why people should switch to Li-Fi?
• Will take time before Li-Fi gains broad
acceptance.

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Challenges
• Driving illumination grade LEDs at high
speeds.
• Increasing data rate with parallelism/arrays.
• Achieving low complexity/low cost
modulation.
• Overcoming the line of sight constraint.
• Achieving seamless interoperability with other
networks.
• Making Li-Fi work in environments with little
or no light.

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Applications
 Line of Sight Applications:
- vehicle to vehicle communication.
- indoor GPS systems.
 RF Avoidance:
- solution for hypersensitivity to radio
frequencies.
- where radio waves cannot be used for
communication or data transfer.

34. 34
Applications
 Indoor Wireless Communication:
- use of a free, unlicensed spectrum.
- unaffected by RF noise.
- most indoor locations would have a
sufficient amount of light sources.
- secure since Li-Fi cannot penetrate
through walls.
 In interactive toys.

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Applications
 Mobile Connectivity:
- Laptops, tablets, smart phones and
other other mobile devices can
interconnect with each other.
- high data rates, increased security.
 RF Spectrum Relief:
- to relieve RF spectrum of excessive
capacity demands of cellular networks.

36. 36
Applications
 Smart Lighting:
- street lamps to provide Li-Fi hotspots.
- to control and monitor lighting and data.
 GigaSpeed Technology
- fastest wireless data transfer.
- transmission rates of up to 10 Gbps, can
be expanded to several 100 Gbps in future.
- 2 hour HDTV film ransfer in less than 30
seconds.

37. 37
Applications
 Hidden Communications:
- military and defense, communications in
hospitals.
 Casinos:
- casinos employ large amount of video
monitoring equipment.
- rich lighting environments could be
harnessed for Li-Fi.

38. 38
Applications
 Retail Analytics:
- rich lighting environment with
abundant light sources for Li-Fi.
- to track the behaviour of individual
shoppers.
- simplifies shopping process.
- Li-Fi to connect to smartphones to link
up people, product and purchasing.

39. 39
Applications
 Spatial Reuse:
- as alternative in areas of high density
wireless communication with 500 or
more users.
- to share some of the load of Wi-Fi.
 Smart Class Rooms:
- Visual inputs for each student.

40. 40
Li-Fi for Education

41. 41
Components of a Li-Fi Enabled
Smart Class
• Transmission Source: a high brightness
white LED.
• Receiving Element: a silicon photodiode.
• Server: database to store all the required
data.
• Interactive board: as an input device and a
monitor, control by touching the board,
connects with the computer and the
projector.

42. 42
Components of a Li-Fi Enabled
Smart Class
• Projector: to project image on to the
interactive board.
• Computer: with smart class applications
connected to the interactive board, server
and projector.
• More student attention.
• Li-Fi enabled connectivity, issues with
wired LAN resolved.

43. 43
Li-Fi Smart Class
• Wired LANs require drilling holes in the
wall, running cables in lofts, fitting sockets,
etc.
• Equipment expensive to install, time
consuming to setup, not flexible and
requires maintenance by skilled
technicians.
• Li-Fi enabled smart classes to solve the
problems.

44. 44
Thank You