Light Fidelity (Li-Fi) is a bidirectional, high speed , fully networked wireless communication technology similar to Wi-Fi. Li-Fi was first put forward by Professor Harald Haas,University of Edinburgh, during a TED Talk in 2011. Li-Fi is a form of visible light communication and a subset of optical wireless communications (OWC) and could be a complement to RF communication (Wi-Fi or Cellular network), or even a replacement in contexts of data broadcasting. It is so far measured to be about 100 times faster than some Wi-Fi implementations, reaching speeds of 224 gigabits per second.

1. Li-Fi

2.  Bidirectional, high speed, fully networked wireless
communication technology like Wi-Fi.
 First proposed by Professor Harald Haas, University
of Edinburg in 2011, that...
 Light bulbs can act as wireless routers.
 Will form visible light communication VLC.
 A subset of optical wireless communication OWC.
 Could be complement to RF communication Wi-Fi or
cellular network.
 Could even replace all for data broadcasting.

3.  It is about 100 times faster than some Wi-Fi systems.
 Speeds up to 224 gigabits per second.
 Can use visible light or infra red and near ultraviolet
spectrum.
 Uses LED as source.
 Current to LED is switched on/off at a rate too high
to be noticed by human eye.
 LED can be dimmed to below human visibility.
 It is short range communication as light can not
penetrate walls.
 Hence more secure from hacking.
 Direct line of sight not required as light reflects
from walls.

4.  VLC uses visible light between 400THz(780nm) to
800THz(375nm) as optical carrier for data
transmission and illumination.
 It uses fast pulses of light to transmit information
wirelessly.
 Main components of system are-
 A high brightness white LED as source.
 A silicon photodiode which is highly responsive to
visible wavelength region.
 LED is switched on/off to generate „1‟ and „0‟.
 As flicker rate is very high, it appears constant to
human eye.

5.  Light bulbs used as data communication medium to
PC, Laptop, Tablet and PDA .
 All devices have photo-detector connected to them.

6.  Unlike RF communication, LI-FI is very useful in
electromagnetic sensitive areas such as aircraft
cabins, hospitals, nuclear power plants..
 Li-Fi can work under water where Wi-Fi fails.
 Transmits on visible light spectrum, which is 10,000
times larger than entire RF spectrum.
 Data rates of over 10 Gbits/s is much faster than
typical fast broadband.
 Li-Fi is expected to be about 10times cheaper than
Wi-Fi.
 But Li-Fi has shorter range than Wi-Fi.
 Li-Fi is highly efficient as LED consumes less energy
as compared to Wi-Fi.
 No licencing required for Li-Fi.
 No harmful radiation for living beings in Li-Fi.

7.  Radio waves can penetrate through walls, hence can
be intercepted and misused, while light can not
penetrate walls, hence highly secure.
TECHNOLOGY SPEED DATA DENSITY
WIRED
Fire Wire (IEEE 1394)
(Apple)
800 Mbps *****
USB 3.0 5Gbps *****
THUNDERBOLT (Apple) 2 X 10 Gbps *****
WIRELESS (Current)
Wi-Fi-IEEE (802.11N) 150 Mbps *
Bluetooth 3 Mbps *
IrDA 4 Mbps ***
WIRELESS (FUTURE)
Wi-Gig 2 Gbps **
Giga-IR 1 Gbps ***
Li-Fi >10 Gbps ****

8.  Part of visible light communication is modelled after
IEEE802 group.
 As IEEE 802.15.7 is getting obsolete, it fails to
accommodate latest technological development in
field of optical wireless communication such as...
 Optical orthogonal frequency division multiplexing
O-OFDM optimized for-
 high data rates,
 multiple access
 energy efficiency
 New standards required for optical wireless
communication.

9.  However IEEE802.15.7 defines physical layer(PHY)
and media access control(MAC) layer.
 Standard delivers required data rates to transmit
audio, video and multimedia services.
 Standard accounts for
 Optical transmission mobility,
 Compatibility with lighting system of building,
 Interference due to ambient light
 MAC layer linking with other layers such as TCP/IP

10.  Defines three PHY layers with different rates:-
 PHY I established for outdoor application from 11.67Kbps
to 267.6Kbps.
 PHY II permits data rates from 1.25Mbps to 96Mbps.
 PHY III used for many emission sources with modulation
method colour shift keying(CSK). 12Mbps to 96Mbps
 Modulation method for PHY I and PHY II are on-off
keying(OOK) and variable pulse position
modulation(VPPM).
 Manchester coding for PHY I and PHY II includes
clock inside transmitted data by representing logic
“0” with OOK symbol „01‟ and logic “1” by OOK
symbol ‟10‟.
 Symbols sent with a DC component to avoid light
extinction during long runs of “0”s.

11.  Constant current of electricity supplied to an LED
light bulb can be varied up and down at extremely
high speed invisible to human eye.
 There is photo-detector to receive light signal and a
signal processing element to convert data into
streamable content.
 Data fed into an LED light bulb are sent at high
speed to photo-detector/photodiode to be converted
into electrical signal.
 Enhanced method is array of LEDs for parallel data
transmission to increase data rate.
 Or a mixture of red, green and blue LEDs to alter
light frequencies for data channel multiplexing.

13.  LED and photodiode are used to send and detect
light.
 Voltage regulator and level shifter on both side
to maintain voltage level.

14.  Prof. Harald Haas demonstrated in 2011,
transmission of video by LED light bulb with a speed
more than 10Mbps.
 In 2011, German scientists succeeded in creating
800Mbps wireless network by using normal red,
green, blue and white LED light bulbs.
 Subsequently, in 2012, Haas setup a company
pureLiFi with aim to become world leader in VLC.
 PureLiFi demonstrated the first commercially
available Li-Fi system, the Li-1st, at 2014 Mobile
World Congress in Barcelona.

15.  PureLi-Fi Demo had three Li-Fi access points, brick-
sized boxes attached to LED down-lighters covering
area of 20sq.m.
 Boxes turned light bulbs to wireless antenna.
 Dongle plugged into laptop or tablet, acts as wireless
modem to received data.
 Dongle plugged via USB also provided power.
 Dongle has sensor to catch light and infra red
component to send signal.
 Overhead lights also have networking component:
 for multiple users to connect to single light
source.
 To move from one light source to another without
losing connection.

17.  PureLiFi already have two products in market:
 Li-Flame Ceiling Unit to connect to an LED light
fixture.
 Li-Flame Desktop Unit which connects to a device
via USB
 PureLiFi is adding this functionality to off-the-shelf
light bulbs and plugging dongles to devices to
receive data.
 PureLiFi COO Burchardt aims to incorporate this
inside devices and LED bulb as application-specific
integrated circuit (ASIC) or System-on Chip(SoC)
module.

18.  Medical Electronics:- Radio waves block signals from
monitoring equipment in hospitals, especially OT.
 Li-Fi can be safely used in medical establishments
with 10000times more spectrum.
 Airlines: Wi-Fi hampers with working of airlines.
 High speed Li-Fi connections can be safely provided
inside airplanes for each seat.

19.  Smarter Power Plants : Power plants need fast
interconnected data system to monitor demand, grid
integrity, core temperature etc. without radiation
interference.
 Li-Fi could offer safe, abundant connectivity for all
such sensitive areas.
 It will give additional benefit of drastic power saving
in terms of technology and use of LED bulbs.

20.  On Road: Li-Fi can communicate with LED lights of
vehicles to reduce accidents.
 Street lamps can be changed to Li-Fi lamps to
transfer data.
 Road blocks and congestions can be controlled by
intimating the drivers about traffic.

21.  Under Sea: For under water ROVs, large cables
supply power and allow signal transmission with
vessels above.
 Limitation of length and risk of damage to wires.
 Sea exploring becomes efficient if instead of wires,
high powered lamps fitted at bottom, are used to
send Li-Fi signals to ROVs.
 Vessels can also use headlamps to communicate with
other vessels or land.
 Data processing and transfer becomes faster and
efficient.

22.  Under Sea:

23.  Multiuser Communication: Li-Fi helps to share
multiple information at a single instance.
 Broadcasting and multiple accessing can be made
available.
 Ceiling lights, street lights etc. can be used as
hotspots to spread internet using VLC at low cost.

24.  Under Li-Fi technology, every bulb can be made to
transmit data.
 Li-Fi will lead to cleaner, greener, safer and brighter
future.
 Will solve problems of RF bandwidth shortage.
 Li-Fi is authentic and very efficient alternative to RF
devices.
 Li-Fi and Wi-Fi are complementary technologies that
will work well in many situations.
 Line-of-sight is major drawback of Li-Fi outdoors.

25.  gimt.edu.in/clientFiles/FILE_REPO/2012/NOV/23/1353645362045/69.pdf
 www.ijedr.org/papers/IJEDRCP1401007.pdf · PDF
 https://en.wikipedia.org/wiki/Li-Fi
 www.sciencealert.com/li-fi-tested-in-the-real-world-for-the-first...
 www.sciencealert.com/li-fi-tested-in-the-real-world-for-the-first-time-is-1...
 www.lifi-centre.com/about-li-fi/what-is-li-fi-technology
 www.seminarsonly.com/computer science/Li-Fi-Technology.php