Mini project presentation on:
Saif aziz absar(1RV11EE047)
Vijeth V S (1RV11EE060)
Date of presentation: 05/05/2014
In present scenario, Radio waves are being used in communication
systems. But visible light can be used to transmit data more faster
Wi-Fi is great for general wireless coverage within buildings,
whereas Li-Fi is ideal for high density wireless data coverage in
confined area and for relieving radio interference issues.
Li-Fi comprises a wide range of frequencies and wavelengths, from
the infrared through visible and down to the ultraviolet spectrum.
Here a sinusoidal signal has been transmitted from one device to
another through visible light.
LI-FI stands for Light-Fidelity.
LI-FI is transmission of data through illumination ,
i.e, sending data through a LED light bulb that
varies in intensity faster than human eye can
Li-Fi can be thought of as a light-based Wi-Fi. That
is, it uses light instead of radio waves to transmit
And instead of Wi-Fi modems, Li-Fi would use
transceiver-fitted LED lamps that can light a room
as well as transmit and receive information.
Wi-Fi (Wireless Fidelity) uses 2.4-5GHz RF to deliver wireless Internet
access and its bandwidth is typically limited to 50-100 megabits per
Optical wireless technologies sometimes called visible light
communication (VLC) and more recently referred to as Li-Fi (Light
Fidelity) on the other hand, offer an entirely new paradigm in
wireless technologies in terms of communication speed, flexibility
The main objective of the project is to provide an
efficient, low cost, secure, digitally controlled and fast
data transfer technique which can be used as an
alternative for conventional data transfer technique Wi-
At the same time the project also lets us to use more
efficient light source i.e., LED.
Our project also aims at a communication tool in public
places which comes up with transfer of data at a faster
rate over a wide spectrum.
The technology truly began during the 1990's in countries like Germany, Korea,
and Japan where they discovered LED's could be switched on & off to send
At TED, Haraald Haas demonstrated a data rate of transmission of around
10Mbps – comparable to a fairly good UK broadband connection. Two months
later he achieved 123Mbps.
On 12th July 2011, he used a table lamp with
an LED bulb to transmit a video of blooming
flowers that was then projected onto a screen
behind him. During the event he periodically
blocked the light from lamp to prove that the
lamp was indeed the source of incoming data.
LED i.e, Light emitting diode can be switched on and off at a
faster rate. The operating speed of LED is less than 1 μs, which the
human eye can’t detect, causing the light source to appear
This invisible on-off activity enables a kind of data transmission
using binary codes.
Switching on the LED is a logical ‘1’, switching it off is a logical
It is possible to encode data in the light by varying the rate at
which LED’s flicker on and off to give different strings of 1s and 0s.
Modulation is so fast that human eye doesn’t notice.
Design of LI-FI
Li-Fi architecture consists numbers of Led bulbs or
lamps, many wireless devices such as PDA, Mobile
Phones, and laptops. Important factors we should
consider while designing Li-Fi as following:
• Presence of Light
• Line of Sight(Los)
• For better performance use fluorescent light & LED
The original information proposed to be sent was data packets consisting
of text or voice information, this would then be decimated by a suitable
ADC or any other converter to produce data bits which were to be
modulated on a suitable algorithm, keeping primarily noise immunity in
The original idea was to modulate the sinusoidal signal using BPSK
technique and use two DSK kits to transmit the sine wave. But since it
required a 100KHz ADC and DACs, which are hardly available, two arduino
processors were used instead of DSK kits.
The sinusoidal signal is given from signal generator to the arduino to which
an LED is connected.
The sinusoidal signal is sampled using arduino at a
particular sampling frequency and then it is given to the
The LED blinks according to sampled signal and thus the
signal is converted to digital signal.
The signal transmitted by the LED is received by a
photoreceptor which is connected to another arduino.
The signal received is decoded and is given to a low pass
The output of the low pass filter is observed in a CRO which
is a sinusoidal signal.
• Consider a sinusoidal carrier. If it is modulated by a bi-polar bit
stream according to the scheme illustrated in Figure below, its
polarity will be reversed every time the bit stream changes polarity.
• This, for a sine wave, is equivalent to a phase reversal (shift). The
multiplier output is a BPSK 1 signal.
• The wave shape is ‘symmetrical’ at each phase transition.
• This is because the bit rate is a sub-multiple of the carrier frequency
• In addition, the message transitions have been timed to occur at a
zero-crossing of the carrier.
• The information about the bit stream is contained in the changes of
phase of the transmitted signal.
One DSK6713 kit
One Function generator
Two ARDIUNO processors
One visible light LED
one self designed low pass filter(2 resistors, 2 capacitors, bread board)
Smart Lighting: Any private or public lighting including street lamps can be used to
provide Li-Fi hotspots and the same communications.
Mobile Connectivity: Laptops, smart phones, tablets and other mobile devices can
interconnect directly using Li-Fi. Short range links give very high data rates and also
Hospital & Healthcare: Li-Fi emits no electromagnetic interference and so does not
interfere with medical instruments, nor is it interfered with by MRI scanners.
Aviation: Li-Fi can be used to reduce weight and cabling and add flexibility to seating
layouts in aircraft passenger cabins where LED lights are already deployed.
Underwater Communications: Due to strong signal absorption in water, RF use is
impractical. Acoustic waves have extremely low bandwidth and disturb marine life.
Vehicles & Transportation: LED headlights and tail-lights are being introduced. Street
lamps, signage and traffic signals are also moving to LED.
Location Based Services (LBS): Highly accurate location-specific information services
such as advertising and navigation that enables the recipient to receive appropriate,
pertinent information in a timely manner and location.
Li-Fi can solve problems related to the insufficiency of radio frequency
bandwidth because this technology uses Visible light spectrum that has
still not been greatly utilized.
High data transmission rates of up to 10Gbps can be achieved.
Since light cannot penetrate walls, it provides privacy and security that
Li-Fi has low implementation and maintenance costs.
It is safe for humans since light, unlike radio frequencies, cannot penetrate
human body. Hence, concerns of cell mutation are mitigated.
Extremely high color fidelity.
Dynamic Dark - Brightness modulation of lamp output to
enhance video contrast
Easy thermal management
Trouble-free integration into existing light engine platforms.
Wide spectrum over the visible wavelength range
Only works if there is direct line of sight (LOS) between the transmitter
Data transmission can be easily obstructed by opaque obstacles.
The use of very high frequencies (400-800THz) limits it to very short
distances and point to point communications only.
Interferences from external light sources like sun light, normal bulbs,
and opaque materials in the path of transmission will cause interruption
in the communication.
High installation cost of the VLC systems.
A major challenge facing Li-Fi is how the receiving device will transmit
back to transmitter.
Whenever the phototransistor is brought in line of sight of
LED and the output of low pass filter is observed in CRO, the
output obtained is as shown below.
It is observed that the above shown sinusoidal waveform is
replaced by random noise as soon as the phototransistor is
moved away from the line of sight of LED.
The possibilities are numerous and can be explored further. If
this technology can be put into practical use , every bulb can
be used something like a Wi-Fi hotspots to transmit wireless
data. Since light is the major source for transmission in this
technology it is very advantageous and implementable in
various fields that can’t be done with the Wi-Fi and other
technologies. Hence the future applications of the Li-Fi can
be predicted and extended to different plat-forms like
education fields, medical field, industrial areas and many
1) ‘Li-Fi: Data through Light’, The Institute of Engineers, Technorama
Magazine, Volume 62, pp. 41, December 2012.
2) http://www.newscientist.com/article/ will-lifi-be-the-new-wifi.html
4) ”Visible-light com-munication: Tripping the light fantastic: A fast and
cheap opti-cal version of Wi-Fi is coming”, The Economist, dated 28 Jan
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