review on light fidelity (li-fi) · pdf fileinternational journal of engineering technology,...

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.comMay 2017, Volume 5, Issue 5, ISSN 2349-4476

226 Sona Sharma, Ankita Singha

Review on Light Fidelity (Li-Fi)

ABSTRACT:Li-Fi stands for Light-Fidelity. Li-Fi technology was proposed by the German physicist - Harald

Haas, which provides transmission of data through illumination by sending data through an LED light bulb

that varies in intensity faster than the human eye can follow. This paper focuses on developing a Li-Fi based

system and analyses its performance with respect to existing technology. 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 provides better bandwidth, efficiency, availability and security

than Wi-Fi. By leveraging the low-cost nature of LEDs and lighting units there are many opportunities to

exploit this medium, from public internet access through street lamps to auto-piloted cars that communicate

through their headlights. Haas envisions a future where data for laptops, smart phones, and tablets will be

transmitted through the light in a room [1].

Keywords: High-brightness LED, Li-Fi, photodiode, Wi-Fi, wireless communication.

INTRODUCTION

In the present day scenario, the transfer of data from one place to another is considered as a day to day

significant task. As a large number of devices access the internet simultaneously, therefore the current

wireless network that connect us to the internet provides slow speed. With the limitation of fixed available

bandwidth, it becomes cumbersome for these networks to provide high data rates and secured network [1].

The available radio spectrum below 10 GHz has become exhausted due to the ever increasing demand for

wireless data communication. The wireless communication industry has responded to this problem by

considering the radio spectrum above 10 GHz. However, according to the Friis free space equation 2fL

as the frequency (f) increases, the path loss (L) increases. In addition, at higher frequencies blockages and

shadowing are more difficult to overcome in terrestrial communication. Hence, the systems must be designed

to enhance the probability of line-of-sight (LOS), typically by using very small cells (about 50 m in radius)

and by using beamforming techniques. From the system capacity perspective, requirement for small cells is

not an issue because reducing cell sizes has been the major contributor for enhanced system performance in

current cellular communications. This concept leads to Li-Fi technology [2].

Li-Fi is referred to as “Light Fidelity” and is an outcome of 21st century. Li-Fi is a continuation of the

trend to move toward higher frequency spectrum has brought about a great revolution in the field of wireless

communication. It can be classified as nanometre-wave communication system and provides bi-directional

multiuser communication. The basic idea behind this technology is that the data can be transmitted through

the LED light whose intensity varies even faster than the human-eyes. Li-Fi is a form of visible light

communication and a subset of Optical Wireless Communications (OWC) which includes infra-red and ultra-

violet communications as well as visible light. But Li-Fi based communication system differs from Visible

light communication (VLC) system as VLC is only applicable for point to point communication system

whereas Li-Fi is a proper wireless based networking system which supports point to multipoint

Sona Sharma

Student

Jaypee Institute of Information Technology

Noida, India

Ankita Singha

Student

Jaypee Institute of Information Technology

Noida, India




communication[3]. However, Li-Fi is unique in the sense that the same visible light energy can be used for

illumination and communication.

The drawback of traditional Wi-Fi routers is that multiple devices in a space can interfere with each other

whereas Li-Fi can use multiple lights in a room without interference, therefore it is known as the optimized

version of Wi-Fi. It could be a complement to RF communication as it is 100 times faster than some Wi-Fi

implementations, reaching a speed of 224 gigabits per second [4].

With Li-Fi, it is possible to encode the data into the light by varying the rate at which the LED‟s flicker ON

and OFF which cannot be noticed by the human eye [4].

1. WHAT’S IDEA OF Li-Fi

1.1 Why it is called Li-Fi

The word Li-Fi is similar to Wi-Fi but it transmits the data through the wireless optical networking technology

which uses light-emitting diodes (LEDs). The Li-Fidoes not require line of sightfrom transmitter to receiver

and unlike Wi-Fi, Li-Fi signals are not subjected to electromagnetic interference[5].

1.2 Li-Fi History

Harald Hass a professor of the university of Edinburgh who begin his research in the field in 2004, gave a

debut demonstration of what he call a LI-FI prototype at the TED Global conference in the Edinburgh on 12th

July 2011.He used a table lamp with a LED bulb to transmit the radio of video of blooming flower 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. At TED Global, Haas demonstrated the data rate

of transmission of around 10Mbps which is Comparable to a good UK broadband connection. After the two

months, he achieved speed of 123Mbps, thus the idea has been around for a while and various other global

teams are also exploring the possibilities [5].

1.3 What is Li-Fi?

Li-Fi is a wireless internet connection standard. However, rather than operating on radio waves, Li-Fi operates

using visible light waves. It provides a high speed, bidirectional networked, mobile communications in a

similar manner as Wi-Fi. Although Li-Fi can be used to off-load data from existing Wi-Fi networks,

implementations may be used to provide capacity for the greater downlink demand such that existing wireless

or wired network infrastructure may be used in a complementary fashion [4].

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.

Li-Fi uses protocols similar to the RF-band 802.11 protocols, with additional standards to eliminate the

impacts of interference and impacts of ambient lighting. However, the technology cannot be deployed in

outdoors in sunlight or in other odd conditions. Apart of this limitation Li-Fi belongs tothe Visible Light

Spectrum(VLC) which is 10,000 times bigger than the radio-wave spectrum and as it operates in a completely

different spectrum therefore is potentially much more energy efficient than Wi-Fi. The infrastructure for Li-Fi,

meanwhile, is already partially in place [4].

1.4 Principle of Li-Fi

The principle of Li-Fi is based on light modulation which certainly isn‟t a new concept, but Hass has utilized

this concept to enable connectivity through simple LED bulbs.

Li-Fi Architecture is based on the concept of Illumination and transmission. It consists of 3 major

components:

i) LED Lamp




ii) Special Li-Fi Microchip

iii) Photo Detector

Heart of Li-Fi technology is high brightness LED‟s. Light emitting diodes can be switched on and off faster

since operating speed of LED‟s is less than 1 μs, than the human eye can detect, causing the light source to be

appear continuously. This invisible ON-OFF activity enables a kind of data transmission using binary codes.

On Switching ON the LED represents a logical „1‟and switching OFF represents a logical „0‟. 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. A light sensitive device (photo detector) receives

the signal and converts it back into original data. This method of using rapid pulses of light to transmit

information wirelessly is technically referred as Visible Light Communication (VLC) [6].

1.5 Suggested Li-Fi Architecture

The idea for novel architecture of Li-Fi technology involves:

a) Main LED Unit (MLU)

b) Agent LED (AL)

c) Li-Fi cloud.

Fig 1:Li-Fi Suggested Architecture [6]

Fig 2: Li-Fi Cloud [6]

The MLU is extended to the ALs where every AL has their own Li-Fi cloud to provide internet and other

services connectivity through light. In this scenario the coverage area from a single node spread to the

multiple nodes in the form of agent LEDs (AL). The main line is connected to the MLU and further it is

extended to small nodes which are LED bulbs or lamps e.g. AL1, AL2, AL3 and AL4. The whole building is

covered by these small nodes and provides wide coverage through light. The user can access the internet with

little mobility inside the building as shown in Fig 1 & 2. The number of ALs depends on the requirements and

internal structure of the buildings [6].




1.5.1Li-Fi Attocell

The small cell concept, however, can easily be extended to VLC in order to overcome the high interference

generated by the close reuse of radio frequency spectrum in heterogeneous networks. The optical AP is

referred to as an Attocell. Since it operates in the visible light spectrum, the optical Attocell does not interfere

with the macro cellular network. The optical Attocell not only improves indoor coverage, but since it does not

generate any additional interference, it is able to enhance the capacity of the RF wireless networks. Li-Fi

Attocells allow for extremely dense bandwidth reuse due to the inherent properties of light waves. The

coverage of each single Attocell is very limited, and walls prevent the system from suffering from co-channel

interference between rooms. This precipitates in the need to deploy multiple access points to cover a given

space. However, due to the requirement for illumination indoors, the infrastructure already exists, and this

type of cell deployment results in the aforementioned very high, practically interference-free bandwidth reuse.

The user data rate in Attocell networks can be improved by up to three orders of magnitude.

Moreover, Li-Fi Attocells can be deployed as part of a heterogeneous VLC-RF network. They do not cause

any additional interference to RF macro- and picocells, and can, hence, be deployed within RF macro, pico

and even femtocell environments. This allows the system to vertically hand-off users between the RF and Li-

Fi subnetworks, which enables both free user mobility and high data throughput. Such network structure is

capable of providing truly ubiquitous wireless network access.

1.5.2 Cellular Network

The deployment of multiple Li-Fi Attocells provides ubiquitous data coverage in a room in addition to

providing nearly uniform illuminance. This means that a room contains many Attocells forming a very dense

cellular Attocell network. A network of such density, however, requires methods for intra-room interference

mitigation while there is no inter-room interference if the rooms are separated by concrete walls. The unique

properties of optical radiation, however, offer specific opportunities for enhanced interference mitigation in

optical Attocell networks. Particularly important is the inability of light to penetrate solid objects, which

allows interference to be managed in a more effective manner than in RF communication.

Fig 3: Illustration of signal contributions to cell-center regions and to conflicting regions [7].

Essential techniques for increasing wireless system capacity such as beamforming are relatively

straightforward to use in VLC as the beamforming characteristic is an inherent, device specific property

related to the field of view (FOV), and no computationally complex algorithms and multiple transmitting

elements are required. The application of multiple simple narrow-emission-pattern transmitters at each

attocellular AP results in significant co-channel interference reduction. The technique allows the cellular

coverage area to be broken down further into areas of low interference and areas that are subject to higher

interference – typically at the cell edges.




2. WORKING TECHNOLOGY OF Li-Fi

2.1Working of Li-Fi

A new generation of high brightness light-emitting diodes forms the core part of light fidelity technology. The

logic is very simple. If the LED is on, a digital 1 is transmitted. If the LED is off, a digital 0 is transmitted.

These high brightness LEDs can be switched on and off very quickly which gives us a very nice opportunities

for transmitting data through light.

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 side. 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 colours, to obtain data rates in the range of hundreds of megabits per second [1].

Fig 4: Working of Li-Fi [1]

Many other sophisticated techniques can be used to dramatically increase VLC data rate. Teams at the

University of Oxford and the University of Edinburgh are focusing on parallel data transmission using array

of LEDs, where each LED transmits a different data stream. Other groups are using mixtures of red, green and

blue LEDs to alter the light frequency encoding a different data channel.

2.2 Li-Fi Construction

The main components of Li-Fi system are as follows:

a) A high brightness white LED which acts as transmission source.

b) A silicon photodiode with good response to visible light as the receiving element.

The Li-Fi System consists of 4 primary sub-assemblies:

i) Printed Circuit Board (PCB)

ii) RF Power Amplifier circuit (PA)

iii) Bulb

iv) Enclosure.

Fig 5: Bulb sub-assembly [1]




i) The PCB: It Controlsthe electric inputs and outputs of the lamp and houses the microcontroller used to

manage different lamp functions.

ii) RF Power Amplifier circuit (PA): An RF (Radio-Frequency)signal is generated by the solid-state PA and is

guided into an electronic field about the bulb. The high concentration of energy in the electric field vaporizes

the contents of the bulb to a plasma state at the bulb‟scenter, this controlled plasma generates an intense

source of light.

iii) Function of The Bulb:At the heart of LIFI™ is the bulb sub-assembly where a sealed bulb is embedded in

a dielectric material. This design is more reliable than conventional light sources that insert degradable

electrodes into the bulb. The dielectric material serves two purposes; first as a waveguide for the RF energy

transmitted by the PA and second as an electric field concentrator that focuses energy in the bulb. The energy

from the electric field rapidly heats the material in the bulb to a plasma state that emits light of high intensity

and full spectrum.

iv) All of these sub-assemblies are contained in an aluminium enclosure [4].

2.3 Modulation Techniques in Li-Fi

In Li-Fi based system, Dimming based modulation schemes are most commonly used modulation schemes

which are single carrier based schemes. In dimming based modulation schemes desire data rate is achieve by

controlling the ON-OFF level of LED. On-off keying (OOK),Pulse Width Modulation (PWM),Pulse position

modulation (PPM), Variable pulse position modulation (VPPM),Overlapping PPM (OPPM) and optical

spatial modulation (OSM) are the main dimming based modulation schemes which can be implemented in Li-

Fi based system.

To achieve higher data rate and to decrease the effect of distortion and interference, multicarrier modulation

can also be useful in Li-Fi based communication system but multicarrier modulation schemes are less energy

efficient. One of the most common schemes is OFDM but OFDM based signal is complex and bipolar in

nature so to implement OFDM for Li-Fi system some modifications are required in conventional technique for

better performance. Some of the OFDM techniques are the direct current (DC) biased optical OFDM (DCO-

OFDM), the asymmetrically clipped optical OFDM (ACO-OFDM) and the asymmetrically clipped DC biased

optical OFDM (ADO-OFDM).The DCO-OFDM adds a DC bias to the bipolar analoguesignal and clips any

remaining negative values insignal. If the DC bias is set a high value, the opticalSNR will become very large,

leading to low optical powerefficiency. ACO-OFDM is proposed to overcome the disadvantagesof DCO-

OFDM which transmits informationonly on odd subcarriers. Besides, the clipping noise is added only on the

even subcarriers, thus it will not interfere with the information on the odd subcarriers. Although ACO-OFDM

is power efficient, its drawback is the low spectrum efficiency which is half of DCO-OFDM and ¼ of

traditional OFDM provided the same digital modulation formats. The ADO-OFDM, combing both ACO-

OFDM and DCO-OFDM, combat their respective disadvantages. In this system, ACO-OFDM is transmitted

on the odd subcarriers and DCO-OFDM is transmitted on the even subcarriers. Therefore, ADO-OFDM

outperforms DCOOFDM in terms of power efficiency and outperforms ACO-OFDM in terms of spectrum

efficiency. The relationship between light emitted by LED and current is nonlinear so this nonlinearity based

nature of LED affects the performance of OFDM based modulation schemes [8].

There are some modulation schemes which are designed to support both purpose of communication and

illumination by using multicolored LEDs. Color shift keying (CSK) is a scheme in which signals are encoded

into color intensities emitted by red, green and blue (RGB) LEDs .The constant color is maintained by

mapping the transmitting bits in to instantaneous chromatics of LEDs to ensure constant luminous flux. CSK

has Reliability on LED performance due to constant luminous flux and has no flicker effect over all

frequencies. Metameric modulation (MM) modulates data in the visible spectrum while maintaining a

constant lighting state.MM has a better Color quality control and higher energy efficiency. Color intensity

modulation (CIM) provides dimming in color space. CIM also satisfy the need of color matching and

increases the data rate in signal space for multicolored LED based system [7].




3. MULTIUSER ACCESS IN Li-Fi

As a wireless broadband technology, Li-Fi can provide multiple users with simultaneous network access.

OFDM provides a straightforward method for multiuser access, i.e., orthogonal frequency division multiple

access (OFDMA), where users are served and separated by a number of orthogonal subcarriers. No fast fading

exists in Li-Fi systems and the indoor optical wireless channel shows the characteristic similar to the

frequency response of a low-pass filter. Hence, subcarriers with lower frequencies generally provide users

with high SNR statistics. Therefore, it is important in OFDMA to use appropriate user-scheduling techniques

to ensure that fairness in the allocation of resources(subcarriers) is maintained.

In order to enhance the throughput of cell edge users, non-orthogonal multiple access (NOMA) was proposed.

NOMA can serve an increased number of users via non-orthogonal resource allocation (RA), and it is

considered as a promising technology for 5G wireless communication. The power-domain multiplexing

scheme of NOMA is used. In this scheme, successive interference cancellation (SIC) is used at the receiver

side to cancel the inter-user interference.

3.1Multiuser Access in Single Li-Fi Attocell

The basic principle of downlink NOMA is shown in Figure6, where the LED broadcasts a super positioned

version of the messages intended for a group of users of interest. Based on power domain multiplexing, the

super positioned signal is given as a summation of signals, with each multiplied by a weighing factor. Due the

fact that the indoor LoS channel is largely deterministic and strongly related to the Euclidean distance of the

transmission link, the channel qualities or the signal-to-interference-plus noise ratios (SINRs) may fluctuate

significantly among users. For this reason, the interfering signal is detected and cancelled in a descending

order of the SINR at each receiver (excluding the user with the worst channel quality). Furthermore, in the

process of signal detection, the interfering signals whose power is smaller than the useful signal power are

treated as noise.

Fig 6:Illustration of NOMA principle (two-user example) [2]

Consider the downlink Li-Fi transmission in a single Attocell, in which the optical access point (AP) is

located in the ceiling and K mobile users are uniformly scattered within a disc underneath. Without loss of

generality, all of the users are first indexed based on their channel conditions, so that h1≤ ・・・ ≤ hk≤

・・・ ≤ hK, where hkrepresents the opticalchannel gain between the k-th user and the Li-Fi AP. In order to

balance user data rate regardless of their geographical locations, the power partition parameters, denoted by ak,

are set so that users with poorer channel equalities are allocated more signal power (a1≥ ・・・ ≥ ak≥ ・・・

≥ aK), at the same time satisfying the total power constraint. Assuming perfect knowledge of the channel state

information (CSI) and SIC signal processing at the receiver side, the Shannon limit on spectral efficiency for

each user, denoted by τk, can be found as:




Kkah

Kk

ah

ah

kkk

K

ki

kk

kkk

)},1({log

,1

)(

1log

2

2

1

2

2

2

(1)

where, represents the transmit SNR at the Li-Fi AP.NOMA can enhance the performance of users at the cell

edge, without significantly deteriorating the performance of other users with better channel qualities [2].

3.2Multiuser Access in Li-Fi Attocell Networks

Fig 7: Illustration of combined use of NOMA and SDMA in a two-cell Li-Fi network. SIC is used to

eliminate interference [2].

Due to the overlapping coverage area of adjacent Li-Fi APs, the cell edge users will experience increased

interference fromneighbouringAttocells. As shown in Figure 8, cell edge user 1in Li-Fi Attocell 1 also

receives the unwanted signal transmitted from the AP in Li-Fi Attocell 2. Therefore, directly using NOMA in

a Li-Fi network cannot efficiently mitigate interference transmitted from adjacent Attocells. A solution to

enhance the performance of cell edge users in a Li-Fi network is the combination of NOMA and SDMA.

SDMA is based on a coordinated multi-point (CoMP)-aided joint transmission technique. Specifically, users

at different locations are served simultaneously with the use of transmit pre-coding (TPC). After the signal

propagating through the optical channel to the receiver side, inter-user interference ismitigated aided by TPC

and SDMA. Take Figure 8 as an example, since user 1 and user 3 can receive signals from both LED 1 and

LED 2, their “spatial signatures,” i.e., optical channel gains, are exploited for designing the TPC vector. As a

result, transmission links from both LEDs are added constructively to help enhance the performance of user 1

and user 3 at the cell edge. CoMP-aided SDMA requires the Li-Fi APs to have knowledge of both the

message data and CSI of user 1 and user 3. In such a Li-Fi network, only the cell edge users are coordinated

for joint transmission. Therefore, the added signalling overhead and complexity in exchange for enhanced

system performance are not significant. Different from Fig 6, where only user 2 needs to cancel the interfering

signal for user 1, in Fig 7, user 2 needs to cancel the pre-coded version of the signals intended for both user 1

and user 3 [2].




4.MODELLING Li-Fi NETWORKS

In a Li-Fi Attocell network, the placement of APs affects the system performance. The light signal from a

neighbouring AP causes interference which limits the SINR. Due to the use of LEDs, coherent transmission is

not possible, and data has to be encoded by means of IM/DD. As a consequence, the frequencies used are

between zero and typically 20MHzfor phosphor-coded commercial white LEDs assuming a blue filter at the

receiver, and between 60–100 MHz for micro-LEDs. In order to provide multiuser access and mitigate CCI,

the available bandwidth can be divided and shared among different optical APs according to the well-known

frequency reuse concept. Frequency reuse is modelled with a parameter Δ. For example, Δ = 3 means that the

available modulation bandwidth is divided into three equal parts and each part is assigned to an AP in a way

that the geometric re-use distance of the same part of the bandwidth is maximised. Since lighting and wireless

data communications are combined the placement of the optical APs is mainly determined by the lighting

design. The effect of the location of Aps is evaluated for four different scenarios as shown in Figure 8. The

models developed for cellular RF networks are used because the principal optimisation objectives are similar,

namely, complete and uniform signal coverage. Similarly, lighting in home and office environments is

designed to illuminate the entire space in a uniform manner. Figure 8 (a) shows the conventional hexagonal

topology widely used in RF cellular networks. This is an idealised model, in which APs are placed

deterministically to form a hexagonal shaped Voronoi tessellation. Another type of the deterministic model is

the square lattice topology, shown in Fig. 8 (c), where the formed Voronoi cells have squared shapes.

Compared with the hexagonal model, the square model is more suitable to model the regular lighting

condition in large offices and public areas. However, the indoor environment typically contains a large

number of „statically random‟ APs, such as ceiling luminaries, desktop lamps and even LED screens.

Therefore, using deterministic models to analyse the performance of such a network is no longer realistic.

Spatial point process provides more accurate and tractable solutions for network interference modelling.

Fig 8: A room of size 20 m × 20 m is considered. The circles in the figure represent the positions of the

optical APs, which are also the room lights, while the dots represent the positions of the terminals which

can be smartphones or ‘things’. Different deployment scenario studied: (a) Hexagonal network model.

(b) PPP network model. (c) square network model. (d) HCPP network model [2].

The homogeneous Poisson point process (PPP) is the most commonly used spatial model studied in ad hoc

networks, in which the number of APs is assumed to follow the Poisson distribution and the APs are

geographically independent of each other. The use of the PPP model for Li-Fi networks is shown in Figure 8

(b). However, in PPP two APs can be arbitrarily close to each other, which is unrealistic. Figure 8 (d) shows

the Mat´ern type I hard-core point process (HCPP) deployment scenario, which includes an additional

parameter c that controls the minimum separation between any two APs in order to address the limitation of

the PPP model in Figure 8 (b) [2].




5.COMPARISON OF Li-Fi AND Wi-Fi

The comparison between Li-Fi and Wi-Fi can be done on the basis of following parameters [4]:

Table 1: Comparison of Li-Fi and Wi-Fi [4]

Parameter Li-Fi Wi-Fi

Capacity Visible light 1000 times than Radio

waves

Radio waves form only a small fraction of the

entire EM spectrum

Efficiency More LEDs consume less energy and

highly efficient

Less Radio Base Stations consume high

amount of energy and most of the energy is

just wasted in cooling down those stations,

thus decreasing the efficiency

Availability Anywhere Limited because of harmful effects

Secure More secure because light waves

cannot penetrate through the walls

and cannot be intercepted by anyone

outside the illumination of LED i,e,

outside the room

Less secure because of high penetrating

power of radio waves

Development

Year

2011 1999

Speed 500Mbps, upto 10 Gbps,100 Gbps 11Mbps

Range 10 metres 10-20 metres

IEEE Standard 802.15.7 802.11b

Spectrum Range 430-770 Thz 3Hz-1000GHz

Network

Topology

Point to point Point to multi-point

Communication Based on Visible Light

Communication

Based on Radiation Frequency

Communication

Carrier Information carried over optical

intensities

Information carried on electric field

Architecture Attocell Femtocell

Modulation Direct Current biased Optical

Orthogonal Frequency Division

Multiplexing(DCO-OFDM)

Direct Sequence Spread Spectrum

Power

Consumption

Less More

Cost Less More

6.APPLICATIONS OF Li-Fi

The applications of Li fi technique in various fields are as follows [7]:

1. Airways: The communications of the airways are based on the radio waves, so that travel during the

airplane problem occurs in communication media. To overcome this problem Li-Fi tech is used. In aircraft

LED lights already deployed, by using this it gives light as well as internet. And no any issue to the aeroplane.




2. Green information technology: Green information technology nothing but the unlike radio waves and other

communication waves effects on human body, birds, etc. Li-Fi never gives these side effects.

3. Mobile connectivity: There are many mobile device like Laptops, smart phones, tablets which is required

high data rate for short range link also security. It is possible in the Li-Fi technology.

4. Applications in sensitive areas: For the safety purpose radio waves are not used in some areas such as

mines, petrochemical plants. In these areas we use the Li-Fi technology which is not harmful for the human.

5. Underwater communication: RF use is impractical dueto strong signal absorption in water. Acoustic waves

have low bandwidth and disturb marine life. Li-Fi is the best solution of this problem.

6. Traffic management: In traffic signals, LED and the Car light LEDs communicate with each other, which

can help in managing the traffic in better manner and the accidents number of decreased.

7. Medical application: In the operation theatres do not allow radio waves. It hazards to the patient‟s health.

To overcome this Li-Fi technology is used.

7.ADVANTAGES OF Li-Fi

Using of Li-Fi provides many advantages as below [6]:

1) Operates on Visible Light Spectrum having 10,000 times more spectrum bandwidth than current RF

spectrum.

2) Visible Light Spectrum is a free spectrum, there is no license process enabled for that by TROI. That

means free of license cost.

3) Visible Light Spectrum uses the Attocell, which not only improves the indoor coverage, but since it does

not generate additional interference, it is able to enhance the capacity of RF wireless networks.

4) Attocellhelps and being the bridge between RF and VLC Li-Fi Sub networks.

5) High Installment cost but low maintenance cost.

6) Uses the LED bulbs which is Cheaper than Wi-Fi

7) Less time & energy Consumption

8) Lower electricity Charges

9) Theoretical speed of 1.3 Gbps by using the different color LEDs we can achieve the more speed of 10

Gbps.

10) Longevity of LED bulb saves money

11) More Expose of VLC spectrum won‟t cause any health problems.

12) Secured access because of light penetration restriction through wall.

13) LiFi can be used as remote signal under water Ocean where RF will not work.

14) Can be used in Petrochemical plants where the RF usage is not secured.

15) Can be used in Hospitals where RF signals cannot be used.

16) Can be used in Auto Driven Cars to avoid the traffic / accident collisions.

17) Can be used in Streets to control the traffic signals also to form the Li-Fi Wi-Fi Network.

8.LIMITATIONS OF Li-Fi

The main problem is that light can‟t pass through objects, so if the receiver is inadvertently blocked in any

way, then the signal will immediately cut out. If the light signal is blocked, or when we need to use our device

to send information, we can seamlessly switch back over to radio waves [10].

1) Reliability and network coverage are the major issues to be considered by the companies while providing

VLC services. Filtering of Interference from external light sources like sun light, normal bulbs; and opaque

materials in the path of transmission work in progress.




2) High installation cost of the VLC systems can be complemented by large-scale implementation of VLC

though adopting VLC technology will reduce further operating costs like electricity charges, maintenance

charges etc.

3) Li-Fi uses light-emitting diodes (LEDs) which are rapidly gaining in popularity for standard light bulbs and

other domestic and commercial purposes. They are expected to be ubiquitous in 20 years. VLC is not in

competition with Wi-Fi, it is a complimentary technology that should eventually help free up much needed

space within the radio wave spectrum.

9. FUTURE TOWARDS Li-Fi

Future can be envisioned having light as transmitting medium to our laptops, smart phones and tablets. And

security wouldn‟t be snapped if the device can‟t access the data. Li-Fi has been in the news a bit recently, with

recent tests yielding wild promises of vastly improved wireless connection speeds and an end to internet

traffic congestion [4]

10.CONCLUSION

The concept of Li-Fi is currently attracting a great deal of interest, not least because it may offer a genuine and

very efficient alternative to radio-based wireless. As a growing number of people and their many devices

access wireless internet, the airwaves are becoming increasingly clogged, making it more and more difficult to

get a reliable, high-speed signal. The unique physical properties of light promise to deliver very densely-

packed high-speed network connections resulting in orders of magnitude improved user data rates. Based on

these very promising results, it seems that Li-Fi is rapidly emerging as a powerful wireless networking

solution to the looming RF spectrum crisis, and an enabling technology for the future Internet-of-Everything.

This may solve issues such as the shortage of radio-frequency bandwidth and also allow internet where

traditional radio based wireless isn„t allowed such as aircraft or hospitals [1].

REFERENCES

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[6]P. Bodke, “A Study on Li-Fi -Advanced Wireless Communication System”, International Journal of Advanced

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[7] U. Sawantet al. “A Review On LI-FI Technology”,International Journal of Scientific Research Engineering &

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34, no. 10, May 15, 2016.

[9] X. Baoet al. “Li-Fi: Light fidelity-a survey”, Springer Science+Business Media New York, 18 Jan. 2015.

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