Post on 02-Oct-2020
Up-and-Coming Li-Fi technology under Visible Light Communication
To transfer the data among multiple users in train
B.Anitha Vijayalakshmi 1, K. Ramkumar
2, A.Aruna3
1Assosiate Professor, Department of Electronics & Communication Engineering
Kings Engineering College
2Professor, Department of Computer Science and Engineering
Kings Engineering College
3Assistant Professor, Department of Electronics & Communication Engineering
Kings Engineering College
Abstract:
One of the essential demands in today‟s lives is sharing of information. With the continually
increasing traffic demand the accessible radio frequency (RF) spectrum with available frequency
was not able to support multiple users in delivering broad band and multimedia content. Wireless
fidelity (Wi-Fi) is great for general wireless exposure in less dense area, whereas light fidelity
(Li-Fi) is ideal for high density wireless data coverage in cramped area and for recreating radio
frequency interference issues. In onboard rail networks the delivering of smooth Wi-Fi access is
critical. The fifth generation (5G) visible light communication (VLC) technology includes
hundreds of terahertz of license free bandwidth, and uses the visible light spectrum in providing
high data rate and security. Li-Fi holds a great scope in future due to its outstanding speed. This
paper focuses on the smart way of data transfer to multiple users in train using Li-Fi technology
under VLC.
Key words: Multiple users, Li-Fi, Train, VLC
I. Introduction
The RF based wireless communication has been holdup due to the spectrum scarcity in RF
spectra. The practice of visible light spectrum is at a halt, intact in condition for communication.
The VLC harmonizes the RF-based mobile communication systems for underhanded high-
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capacity mobile data networks. The attention towards VLC using the wavelength of 380–780 nm
is due to its enormous communication bandwidth, unregulated spectrum, high data rate services,
and license-free predominantly. Obvious visible light signals don't infiltrate through the vast
majority of the surfaces in the earth so that it offers inborn remote correspondence security. In
where a VLC framework is conveyed, data might be contained inside the restricted space of the
particular premises. This for all intents and purposes takes out the possibility of casual
eavesdropping.
Customary fluorescent and incandescent light sources can be quickly supplanted by light
emitting diode (LED) because of its vitality efficiency and longer lifetime with the end goal of
brightening. The utilization of LEDs in VLC creates scope for communication together with
illumination. A LED as a transmitter and a photodiode (PD) as a detector can be comprehend in
VLC system. Coherent modulation/detection techniques are not possible in VLC due to the
incoherent emission of the LED. Therefore, intensity modulation with direct detection techniques
has to be used to encode data. In LEDs, data is modulated into the intensity of the light source
and transmission takes place across an optical wireless channel.
To ensure the passengers with real time multimedia information, access to social networks in
station or in train and to meet the traffic demand it‟s required to put in place the broadband
telecommunication networks, using a variety of technologies whether fixed or wireless [2].
Heterogeneity of networks like Wi-Fi, GSM-R, Satellite, 3G / 4G networks is becoming a real
headache for train operators and infrastructure managers [2]. The VLC technology combines
communication in addition to illumination and also affords security, intelligent lighting, indoor
localization and much more. In the future prospects of 5G wireless access networks the VLC
technology will show its greater impact due to its inherent advantages.
II. Issues with RF technology
a) Capacity: Wireless information is transmitted through radio waves which has constrained
transfer speed and costly.
b) Efficiency: There are 1.4 million cell radio base stations that expend monstrous measure of
vitality. In this way productivity of such base stations is just 5%.
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c) Availability: It isn't prudent to utilize cell phones in aeroplanes and at places like
petrochemical plants and oil pumps.
d) Security: Radio waves can penetrate through walls. They can be intercepted. If someone has
knowledge and bad intentions, they may misuse it [2].
The need to utilize visible light as medium depends on: Low usage cost – by basic establishment
methodology and installation of LEDs. Low support cost – by low power utilization and long
life-time of LEDs.
III. Visible light communication
The part of the VLC spectrum which is visible to the human eye is the visible light spectrum.
The band width of this range connects to 430-770 THz. Imagine that how a flash light can be
used to send the mores code. If the flash` light is made on and off very quickly according to the
binary data of user requirement we get a system wherein there is communication plus
illumination. The availability of the large bandwidth in VLC resolves the low bandwidth
problem in RF communication as illustrated in Fig. 1. The VLC receiver only receives signals if
they reside in the same room as the transmitter, therefore the receivers outside the room of the
VLC source will not be able to collect the signals and thus, it has the protection from security
issues that happens in the RF communication systems.
.
Fig.1 Visible light spectrum
As an obvious light source can be utilized both for illumination and communication, in this
manner, it spares the further power that is required in RF communication. Keeping in perception
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the above advantages, VLC is one of the confident competitors on account of its highlights of
non-licensed channels, high bandwidth and low power consumption.
A. Feasibility of VLC technology
Global Positioning System (GPS) is a famous positioning system nowadays. In fact, the visible
light communication system could be installed into the street lamps. The blind spots problem in
GPS could be tackled. Also, the errors in detecting the actual position could be reduced. LED
commercial displays can be seen everywhere. The displays could be used as the wireless
communication transmitters [3]. As there is a rapid growth in population, the increase in the
number of devices accessing the wireless internet, the airwaves becoming increasingly clogged,
making it more and more difficult to get a reliable and high-speed data transmission. Li-Fi may
solve the above issues and overcome the shortage of radio frequency bandwidth and also allow
internet to be used in the places where traditional radio based wireless communication isn‟t
allowed such as aircraft or hospitals [4].
In Wi-Fi reduction in speed and the jamming take place which is today‟s problem as the number
of users are increasing and also waves create a harmful effect for living things. This jamming
problem get reduces to a great extent by using Li-Fi and such that we can precede towards the
cleaner, greener, safer and brighter future without radio wave. Li-Fi using LED‟s can be
encouraged to produce a safe and green technology. Li-Fi will bring out Li-Fi products for firms
installing LED-lighting systems. In future, data for laptops, Smartphone‟s, and tablets can be
transmitted through the light in a room by using Li-Fi [5].
Fig. 2: Li-Fi module
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LEDs switches speedily to “ON” and “OFF such that human eye cannot recognize the operating
speed of LEDs and thereby causing the light source to appear to be constantly ON. This
undetectable ON-OFF activity allows data transmission via binary codes. Switching ON an LED
is binary „1‟, switching it OFF is binary „0‟. It is conceivable to encode information in light by
fluctuating the rate at which LEDs flicker ON and OFF to give different strings of 1s and 0s.
Modulation is rapid to the point that people can't see it. A light sensitive device (photo detector)
then collects the signal and converts it again to original data.
B. Li-Fi technology
Li-Fi is a high hustle bi-directional completely connected, visible light wireless communication
system and is equivalent to Wi-Fi, which uses radio frequency for communication. The Wi-Fi
signals have the issue of interference with other RF signals. The objective of Li-Fi Consortium
is to encourage the Development and dissemination of optical remote advancements, navigation,
natural user interfaces and others. There are around 14 billion lights around the world, they
simply should be supplanted with LED ones that transmit information," says Haas. "We figure
VLC is a factor of ten times less expensive than Wi-Fi." Since it utilizes light rather than radio-
frequency signals, VLC could be utilized securely in Aircraft, combined into medical devices
and hospitals where Wi-Fi is prohibited, or even underwater, where Wi-Fi doesn't work by any
means. Li-Fi innovation utilizes a piece of the electromagnetic range that is as yet not
extraordinarily expended. The Visible Light Spectrum is in actuality particularly a part of our
lives for many years and does not have any real sick impact. Besides there is 10,000 times more
space accessible in this range and simply incorporating on the bulbs being used, it likewise
increases to 10,000 times greater accessibility as a framework, all inclusive.
IV. General purpose illumination with LED technology
The VLC technology‟s vital source is LED. Universally useful enlightenment for home, open
spots and enterprises request white or amber lighting. By and by, lighting organizations are
occupied with growing high power white LED bunches for such applications by accomplishing
comparable light yield as incandescent or fluorescent lamps while reducing power wastage. In
the years that took after, high brightness white LEDs were formed by mixing of high power blue
LED with yellow phosphors, white phosphor LEDs have recently reached luminous efficacies of
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150 lm/W. White Light from (R/G/B) LEDs directly mixes light in required proportions from
three i.e., red, green and blue (RGB) LEDs to produce white light of desired chromaticity. The
luminous efficacy of this “RGB” solution is very high, with about 29 lm/W.
The LEDs can create the white light illumination in two ways, the blue emitters with phosphor
layer and red–green–blue–amble (RGBA) emitters. The phosphor-based LEDs has enhanced
data rate, higher bandwidth than RGB LEDs. Recently, data rates in excess of 1 Gbps has been
reported using off-the-shelf phosphor-coated white LEDs and 3.4 Gbps has been demonstrated
with an off-the-shelf red-green-blue (RGB) LED. Another similar Gigabit/s wireless system with
phosphor-coated white LEDs has been demonstrated using a 4×4 multiple-input-multiple-output
(MIMO) configuration [6]. LED encourages with unmatched energy proficiency and life
expectancy. The acknowledgment of LEDs practice will be of steady in ascend in future because
of its conservative frame factor, diminished utilization of unsafe materials in outline and lower
warm age in long stretch of unremitting use.
Fig.3 LEDs installed in train
The LEDs are equipped in changing to various light intensity levels imperceptible by a human
eye at a very fast rate when comparable with older illumination technologies. The data will be
encoded in the emitting light and the photo detector referred as light sensor, receives the
modulated signals and decodes the data. This implies the LEDs can give out both the double
purpose of illumination and communication.
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V. Problem in employing Wi-Fi on onboard rail networks
In onboard rail networks the delivering of smooth Wi-Fi access is critical. Onboard environments
are inclined to vibrations, have constrained space and it requires altered wireless devices to
ensure system stability. The wireless devices used in onboard must make sure that each traveler
has dispensed adequate transfer speed and gave secured arrange access, without being on edge
about being hacked.
Fig.4 Problem of hacking
Most of the passengers in high-density trains, anticipate that web access is to read messages or
watch online recordings. The onboard network designers must think about the sort of utilizations
that travelers are habituated to practice over the web. So that they may eliminate the possibility
of the train‟s passengers troubled by unstable internet access. To ensure the safety in onboard
systems from hackers connected to the same network topology, the public network environments
must be protected and the privacy of passengers must be preserved for those who access the
train‟s Wi-Fi access point (AP)s.
Fig.5 Unstable connectivity in dense environment
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VI. System implementation:
In onboard train, the recommended block is shown in Fig. 3 [7] to provide effective data
transmission from the base station to receiving station.
Fig.5 Recommended block
The system has a Li-Fi RF driver to sense the signal from the base station using the medium of
light and the photo detector in the device captures the signal and passes the information to the
passengers. „1‟ is transmitted if the LED is on; if it‟s off the transmitted output is „0‟. LEDs can
be toggled on and off very quickly, such that it offers pleasant opportunities for transmitting
data. Li-Fi can‟t replace conventional radios altogether, but it could enhance the development of
wireless data transmission inside the train in terms of speed and make it easier to throw a
wireless signal to the multiple users without interruption.
Fig.6 Transmitter module
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Transmitter section consists of PC where the data input is given. The given input is encrypted by
Manchester coding. The encrypted data is stored in the low power microcontroller. The stored
data in the microcontroller is then fed to the Li-Fi module which consists of driver circuit and
LED. By varying the current given to the LED the optical output also varies at high speed. Thus
the binary data from PC is given to Li-Fi module where electrical signal is converted into light
signal.
Fig.7 Receiver module
Then the light signal is received into the receiver side which consists of photo detector. It
converts light signal to electrical signal. Then the binary data from photo detector is given in to
PC where the decryption is done. Thus the user can view the original form of files. The figure 8
shows the uninterrupted communication that can be supplied by Li-Fi under the avoidance of
problem of hacking.
Fig.8 Li-Fi supports uninterrupted communication
The figure 9 shows Li-Fi module for data transmission. In our work video file transmission at a
rate of 9.6 kbps has been achieved at a distance of 50 cm. The work has been carried out in
indoors.
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Fig.9 Li-Fi module for data transmission
VII. Conclusion
Visible light communication using Li-Fi technology will be the best solution in the future for
better illumination and communication inside trains using LED luminaire for lighting system.
The concept of Li-Fi is now inviting a great deal of interest. It offers a genuine and very efficient
substitute to radio-based wireless. Li-Fi is the optical wireless communication for data, audio and
video streaming in LEDs, this type of new invention can be stimulated to produce a safe and
green technology. Li-Fi is still in its incipient stages and thus offers tremendous scope for future
research and innovation.
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