Li-Fi (Light Fidelity) –The Future Technology In Wireless Communication CHAPTER 1 INTRODUCTION Li-Fi is transmission of data through illumination by taking the fiber out of fiber optics by sending data through a LED light bulb that varies in intensity faster than the human eye can follow. Li-Fi is the term some have used to label the fast and cheap wireless-communication system, which is the optical version of Wi-Fi. The term was first used in this context by Harald Haas in his TED Global talk on Visible Light Communication. “At the heart of this technology is a new generation of high brightness light- emitting diodes”, says Harald Haas from the University of Edinburgh, UK,”Very simply, if the LED is on, you transmit a digital 1, if it’s off you transmit a 0,”Haas says, “They can be switched on and off very quickly, which gives nice opportunities for transmitted data.”It is possible to encode data in the light by varying the rate at which the LEDs flicker on and off to give different strings of 1s and 0s.The LED intensity is modulated so rapidly that human eye cannot notice, so the output appears constant. More sophisticated techniques could dramatically increase VLC data rate. Terms at the University of Oxford and the University of Edingburgh are focusing on parallel data transmission using array of LEDs, where each LED transmits a different data stream. Other group are using mixtures of red, green and blue LEDs to alter the light frequency Dept. of Computer Science & Engineering Page 1
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Li-Fi (Light Fidelity) –The Future Technology In Wireless Communication
CHAPTER 1
INTRODUCTION
Li-Fi is transmission of data through illumination by taking the fiber out of fiber
optics by sending data through a LED light bulb that varies in intensity faster than the
human eye can follow. Li-Fi is the term some have used to label the fast and cheap
wireless-communication system, which is the optical version of Wi-Fi. The term was first
used in this context by Harald Haas in his TED Global talk on Visible Light
Communication. “At the heart of this technology is a new generation of high brightness
light-emitting diodes”, says Harald Haas from the University of Edinburgh, UK,”Very
simply, if the LED is on, you transmit a digital 1, if it’s off you transmit a 0,”Haas says,
“They can be switched on and off very quickly, which gives nice opportunities for
transmitted data.”It is possible to encode data in the light by varying the rate at which the
LEDs flicker on and off to give different strings of 1s and 0s.The LED intensity is
modulated so rapidly that human eye cannot notice, so the output appears constant. More
sophisticated techniques could dramatically increase VLC data rate. Terms at the
University of Oxford and the University of Edingburgh are focusing on parallel data
transmission using array of LEDs, where each LED transmits a different data stream.
Other group are using mixtures of red, green and blue LEDs to alter the light frequency
encoding a different data channel.Li-Fi, as it has been dubbed, has already achieved
blisteringly high speed in the lab. Researchers at the Heinrich Hertz Institute in Berlin,
Germany have reached data rates of over 500 megabytes per second using a standard
white-light LED. The technology was demonstrated at the 2012 Consumer Electronics
Show in Las Vegas using a pair of Casio smart phones to exchange data using light of
varying intensity given off from their screens, detectable at a distance of up to ten metres.
In October 2011 a number of companies and industry groups formed the Li-Fi
Consortium, to promote high-speed optical wireless systems and to overcome the limited
amount of radio based wireless spectrum available by exploiting a completely different
part of the electromagnetic spectrum. The consortium believes it is possible to achieve
more than 10Gbps, theoretically allowing a high-definition film to be downloaded in 30
seconds.
Dept. of Computer Science & Engineering Page 1
Li-Fi (Light Fidelity) –The Future Technology In Wireless Communication
Figure-1.1: Li – Fi Environment
Dept. of Computer Science & Engineering Page 2
Li-Fi (Light Fidelity) –The Future Technology In Wireless Communication
Chapter-2
SYSTEM DESIGN
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. This very property of optical current is used in Li-
Fi setup. The operational procedure is very simple-,data from the internet and local
network is used to modulate the intensity of the LED light source if any undetectable to
the human eye. The photo detector picks up signal, which is converted back into a data
stream and sent to the client.
The client can communicate through its own LED output or over the existing
network. An overhead lamp fitted with an LED with signal-processing technology
streams data embedded in its beam at ultra-high speeds to the photo-detector. A receiver
dongle then converts the tiny changes in amplitude into an electrical signal, which is then
converted back into a data stream and transmitted to a computer or mobile device.
Dept. of Computer Science & Engineering Page 3
Li-Fi (Light Fidelity) –The Future Technology In Wireless Communication
Figure-2.1: Data Transmission Using LED
2.1 Methods of Visible Light Communication
Devices used for Visible Light Communication
Communication using Image Sensors
Devices used for Visible Light Communication
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Li-Fi (Light Fidelity) –The Future Technology In Wireless Communication
Transmitter Device Receiver Device
Figure-2.2: Methods of Visible Light Communication
Transmitter device of visible light communication
Visible Light LED
LED light intensity is modulated by controlling its current.
Data rate: low speed to very high speed (up to several hundred Mbps)
Figure-2.3: Visible Light LED
Fluorescent Lamp
FSK modulation of high frequency fluorescent light.
Data rate: up to several kilo bps.
Figure-2.4: Fluorescent Lamp
Receiver device of visible light communication
PIN photo diode
Dept. of Computer Science & Engineering Page 5
Visible Light
Li-Fi (Light Fidelity) –The Future Technology In Wireless Communication
A PIN diode is a diode with a wide, lightly doped 'near' intrinsic
semiconductor region between a p-type semiconductor and an n-type semiconductor
region. The p-type and n-type regions are typically heavily doped because they are used
for Ohmic contacts.
The wide intrinsic region is in contrast to an ordinary PN diode. The wide intrinsic
region makes the PIN diode an inferior rectifier (one typical function of a diode), but it
makes the PIN diode suitable for attenuators, fast switches, photo detectors, and high
voltage power electronics applications.
Operation:
A PIN diode operates under what is known as high-level injection. In other words,
the intrinsic "i" region is flooded with charge carriers from the "p" and "n" regions. Its
function can be likened to filling up a water bucket with a hole on the side. Once the
water reaches the hole's level it will begin to pour out. Similarly, the diode will conduct
current once the flooded electrons and holes reach an equilibrium point, where the
number of electrons is equal to the number of holes in the intrinsic region. When the
diode is forward biased, the injected carrier concentration is typically several orders of
magnitude higher than the intrinsic level carrier concentration. Due to this high level
injection, which in turn is due to the depletion process, the electric field extends deeply
(almost the entire length) into the region. This electric field helps in speeding up of the
transport of charge carriers from P to N region, which results in faster operation of the
diode, making it a suitable device for high frequency operations.