Li-Fi Techonology - · PDF fileInternational Journal of Engineering Technology, Management and Applied Sciences December 2014, Volume 2 Issue 7, ISSN 2349-4476

International Journal of Engineering Technology, Management and Applied Sciences
www.ijetmas.com December 2014, Volume 2 Issue 7, ISSN 2349-4476
45 Priti Mankar, Manisha Mankar
Li-Fi Techonology
Priti Mankar, Department of Elect.Engineering ,PIIT,New Panvel,NaviMumbai, Maharashtra
Manisha Mankar, Department of E&C, MIT,Gondia,Maharashtra
ABSTRACT
Now a days many people are using internet to accomplish their task through wired or wireless
network. As number of users get increased in wireless network speed decreases proportionally.
Though Wi-Fi gives us speed up to 150mbps as per IEEE 802.lln, it is still insufficient to
accommodate number of desired users. Li-Fi is a latest technology that makes use of LED light
which helps in the transmission of data much faster and flexible than data that can be transmitted
through Wi-Fi. Light Fidelity is a branch of optical wireless communication which is an
emerging technology. By using visible light as transmission medium, Li-Fi provides wireless
indoor communication. The bit rate achieved by Li-Fi cannot be achieved by Wi-Fi.
Keywords Li-Fi, LED, Wi-Fi, VLC
INTRODUCTION In simple terms, Li-Fi can be thought of as a light-based Wi-Fi. That is, it uses light instead of
radio waves to transmit information. 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. Since simple
light bulbs are used, there can technically be any number of access points. The basic ideology
behind this technology is that the data can be transmitted through LED light whose
intensity varies even faster than the human eye. As the transmission of the data takes
place through the light emitting diodes (LEDs) the amount is comparatively small .In modern
times, it is called as the optimized version of WI-FI .The advantageous thing is the wireless
communication which decreases the cost enormously.
DR.HARALD HASS, who is considered to be the father of Li-fi from university of Edinburgh,
UK says that the heart of this technology lies in the intensity and the potential of the light
emitting diodes. As there are more and more devices coming up day-by-day the signals are
being clogged up due to heavy traffic, there arose a need for an error free transmission
technology. And the solution to this problem was the Li-fi technology. It has been designed in
such a way that it overcomes the disadvantages that occurs during the usage of Wi-Fi.
The demonstration took place using two Casio smart phones. The data was made to exchange
between the phones using light. Even though the distance was nominal, it is sure that there
would be a rapid increase in the distance of transmission.
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1. WORKING TECHNOLOGY
1.1 Light Fidelity:
Li-Fi technology is a wireless communication system based on the use of visible light between the blue
(670 THz) and red (480 THz). Unlike Wi-Fi which uses the radio part of the electromagnetic spectrum,
Li-Fi uses the optical spectrum. The principle of Li-Fi is based on sending data by amplitude modulation
of the light sources in a well-defined and standardized way. Li-Fi is typically implemented using white
LED light bulbs at the downlink transmitter. These devices are normally used for illumination only by
applying a constant current. However, by fast and subtle variations of the current, the optical output can
be made to vary at extremely high speeds. . All one has to do is to vary the rate at which the LEDs flicker
depending upon the data we want to encode. Further enhancements can be made in this method, like using
an array of LEDs for parallel data transmission, or using mixtures of red, green and blue LEDs to alter the
lights frequency with each frequency encoding a different data channel. Such advancements promise a
theoretical speed of 10Gbps meaning one can download a full high-definition film in just 30 seconds.
1.2 Data Transmission:
The working procedure is very simple, if the light is on then transmits a digital 1; if its off
transmit a 0. The LEDs can be switched on and off very quickly which gives nice opportunities
for transmitting data. Information can therefore been coded in the light by varying the rate at
which the LEDs flicker on and off to give different strings of 1s and 0s. This method of using
rapid pulses of light to transmit information wirelessly is technically referred to as Visible Light
Communication (VLC), though its potential to compete with conventional Wi-Fi has inspired
the popular characterization Li-Fi.
Fig 1: Li-Fi works
1.3 Visible Light Communication:
At first Radio waves, it is expensive and less secure. Infrared, due to eye safety regulation can
only base with low power. Gama rays cannot be used as they could be dangerous. Ultraviolet
light is good for place without people, but otherwise dangerous for the human body .But, visible

rays is safe to use larger bandwidth. VLC is a data communication medium, which uses visible
light between 400 THz (780 nm) and800 THz (375 nm) as optical carrier for data transmission
and illumination. Fast pulses are used for wireless transmission.
Fig 2: VLC
1.4 Transfer medium (fiber optic): Generally, fiber optic cables are wires that transmit data through a extremely thin layer of glass
or plastic fiber threads. The relation between fiber optic thread and Li-Fi is that light signals
travel through these fibers in form of light and then translated to 1s and 0s, the data part.
However fiber optics are extremely expensive but massive bandwidth availability can do away
with that and hence may soon replace most existing wired cables and the change has already
started initiating.
2. DESIGN IF Li-Fi Li-Fi architecture consists numbers of Led bulbs or lamps, many wireless devices such as PDA,
Mobile Phones, and laptops. Important factors to consider while designing Li Fi as following:
1. Presence of Light must be line-of-sight.
2. Lamp driver where internet connection, switch and LED lamp connected.
3. For better performance use LED bulbs.
4. A photo detector received data.
The working of Li-Fi is very simple. There is a light emitter on one end, for example, an LED,
and a photo detector (light sensor) on the other. The photo detector registers a binary one when
the LED is on; and a binary zero if the LED is off. To build up a message, flash the LED
numerous times or use an array of LEDs of perhaps a few different colors, to obtain data rates in
the range of hundreds of megabits per second. The block diagram of Li-Fi system is shown in
Fig. 3.
3. COMPARISION BETWEEN LI-FI & WI-FI
Li-Fi is the name given to describe visible light communication technology applied to obtain
high speed wireless communication. It derived this name by virtue of the similarity to Wi-Fi. Wi-
Fi works well for general wireless coverage within buildings, and Li-Fi is ideal for high density
wireless data coverage inside a confined area or room and for relieving radio interference issues.
Table I shows a comparison of transfer speed of various wireless technologies. Table II shows a
comparison of various technologies that are used for connecting to the end user. Wi-Fi currently
offers high data rates. The IEEE 802.11.n in most implementations provides up to 150Mbit/s
although practically, very less speed is received.

Fig 3: Block diagram of Li-Fi system
TABLE I. COMPARISON OF SPEED OF VARIOUS WIRELESS TECHNOLOGIES
Technology Speed
Wi-Fi IEEE 802.11n 150 Mbps
Bluetooth 3 Mbps
IrDA 4 Mbps
Li Fi >1 Gbps
TABLE II. COMPARISON OF TECHNOLOGIES USED FOR CONNECTING TO THE END USER
Technology Connection Security Reach Cost Bandwidth
Expansion
Wi-Fi Wireless-
EMF Good Excellent High Limited
Hardwired Cables Excellent Fair High Limited
Li-Fi Wireless-
light Excellent Excellent Low Exceptional

4. BENEFITS OF LI-FI OVER WI-FI
1. Capacity Bandwidth: The visible light spectrum is plentiful (10,000 more than RF spectrum), unlicensed
and free to use. Data density: Li-Fi can achieve about 1000 times the data density of Wi-Fi because visible light
can be well contained in a tight illumination area whereas RF tends to spread out and cause
interference.
High speed: Very high data rates can be achieved due to low interference, high device
bandwidths and hig

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Li-Fi Techonology - · PDF fileInternational Journal of Engineering Technology, Management and Applied Sciences December 2014, Volume 2 Issue 7, ISSN 2349-4476