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LI-FI:Light Fidelity
APURVA
Department of Electronics and Communication Engineering Suresh gyanvihar university, Jaipur(Rajasthan) apurva.chandndergupt@gmail.com
Abstract: Li-Fi stands for Light-Fidelity. The technology is very new and was proposed by the German physicist Harald Haas in 2011. Li-Fi provides transmission of data through illumination by sending data through an LED light bulb that varies in intensity faster than human eye can follow. In this paper, the authors will discuss the technology in detail and also how Wi-Fi can be replaced by Li-Fi. Wi-Fi is useful for general wireless coverage within buildings while Li-Fi is ideal for high density wireless data coverage in confined areas where there are no obstacles. Li-Fi is a wireless optical networking technology that uses light emitting diodes (LEDs) for transmission of data. The term Li-Fi refers to visible light communication (VLC) technology that uses as medium to deliver high-speed communication in a manner similar to Wi-Fi. Li-Fi provides better bandwidth, efficiency, availability and security than Wi-Fi and has already achieved high speeds in the lab. In the present paper the authors will give a detailed study on Li-Fi technology, its advantages and its future scope.
Keywords: Light Fidelity; LED; VLC; Wi-Fi; Bandwidth.
I. I NTRODUCTION
Professor Harald Haas, the Chair of Mobile Communications at the University of Edinburgh, is recognized as the founder of Li- Fi. He coined the term Li-Fi and is the co-founder of pureLiFi. He gave a demonstration of a Li-Fi prototype at the TED Global
conference in Edinburgh on 12 th^ July 2011. He used a table
lamp with an LED bulb to transmit a video of a blooming flower that was then projected onto a screen. During the talk, he periodically blocked the light from the lamp with his hand to show that the lamp was indeed the source of the video data. Li- Fi can be regarded as light-based Wi-Fi, i.e. instead of radio waves it uses light to transmit data. In place of Wi-Fi modems, Li-Fi would use transceivers fitted with LED lamps that could light a room as well as transmit and receive information. It
makes use of the visible portion of the electromagnetic spectrum which is underutilized. Li-Fi can be considered better than Wi-Fi because there are some limitations in Wi-Fi. Wi-Fi uses 2.4 – 5 GHz radio frequencies to deliver wireless internet access and its bandwidth is limited to 50-100 Mbps. With the increase in the number of Wi-Fi hotspots and volume of Wi-Fi traffic, the reliability of signals is bound to suffer. Security and speed are also important concerns. Wi-Fi communication is vulnerable to hackers as it penetrates easily through walls. In his TED talk, Professor Haas highlighted the following key problems of Wi-Fi that need to be overcome in the near future:
a. Capacity: The radio waves used by Wi-Fi to transmit
data are limited as well as expensive. With the development of 3G and 4G technologies, the amount of available spectrum is running out.
b. Efficiency: There are 1.4 million cellular radio masts
worldwide. These masts consume massive amounts of energy, most of which is used for cooling the station rather than transmission of radio waves. In fact, the efficiency of such stations is only 5%.
c. Availability: Radio waves cannot be used in all
environments, particularly in airplanes, chemical and power plants and in hospitals.
d. Security: Radio waves can penetrate through walls.
This leads to many security concerns as they can be easily intercepted.
Li-Fi addresses the aforementioned issues with Wi-Fi as follows:
a. Capacity: The visible light spectrum is 10,
times wider than the spectrum of radio waves. Additionally, the light sources are already installed. Hence Li-Fi has greater bandwidth and equipment which is already available.
b. Efficiency: LED lights consume less energy and are
highly efficient.
c. Availability: Light sources are present in all
corners of the world. Hence, availability is not an issue. The billions of light bulbs worldwide need only be replaced by LEDs.
d. Security: Light of course does not penetrate through
walls and thus data transmission using light waves is more secure.
Table-1: Advantages of Li-Fi
Light LEDs produce more light per watt than do incandescent bulbs
ON- OFF Time
LEDs can light up very quickly
Toxicit y
Unlike fluorescent lamps, LEDs do not contain mercury Free Band
Li-Fi makes use of a free band that does not need any licensing High Speed s
It offers theoretical speeds in the order of Gigabits per second
Airlin es
Li-Fi can be used safely in aircrafts without affecting airline signals unlike Wi-Fi Health care
It can be integrated into medical devices and in hospitals as no radio waves are involved Under water
Wi-Fi does not work underwater but Li-Fi does and hence can be used for undersea explorations Traffic Contro l
Li-Fi can be used on highways for traffic control applications. Cars can have LED based headlights and
LED based backlights that can communicate with those of other cars and prevent traffic accidents Street Lamps
Every street lamp can be converted into a free data access point Spectr um
The issues of the shortage of radio frequency bandwidth can be sorted out by Li-Fi Relief
Frank Deicke, who leads Li-Fi development at Fraunhofer Institute for Photonic Microsystems in Dresden, Germany, has said that Li-Fi can achieve the same data rates as USB cables which is challenging for wireless technologies such as Bluetooth and Wi-Fi. He also cites another advantage of Li-Fi being that the latency of Li-Fi is in the order of microseconds where as that of Wi-Fi is in the order of milliseconds. With the above benefits encouraging us to adopt this new technology, the actual need for Li-Fi can be confirmed from Cisco’s Visual Network Index which suggests that user demand is increasing faster than gains in spectral efficiency. By 2015, traffic from wireless devices is expected to exceed that from wired devices. Such increases in network traffic require significant changes in how we think of wireless communication and Li-Fi may be the change that we need.
Fig-1: Electromagnetic wave spectrum
avoidance and data acknowledgement protocols. The physical layer is divided into 3 types: PHY I, II, III and employ a combination of different modulation schemes.
In order to actually send out data by means of LEDs, it is required to modulate these into a carrier signal. The carrier signal consists of light pulses sent out at short intervals. The manner in which this is done depends on the modulation scheme employed.
Li-Fi systems use the following different modulation schemes:
1. On-Off Keying (OOK): The 802.15.7 standard uses
Manchester coding so that the period of positive pulses is same as the period of negative ones, however this doubles the bandwidth required for transmission. For higher bit rates, run length limited (RLL) coding is used which is spectrally more efficient. Dimming is supported by adding an OOK extension which adjusts the aggregate output to the correct level.
2. Variable Pulse Position Modulation (VPPM): PPM
encodes the data using the position of the pulse within a set time period. The duration of the period containing the pulse must be long enough to allow different positions to be identified. VPPM is similar to PPM but it allows the pulse width to be controlled to support light dimming.
- Colour Shift Keying (CSK): This is used if the illumination system uses RGB-type LEDs. By combining different colours of light, the output data can be carried by the colour itself and hence the intensity of the output can be near constant. Mixing of RGB primary sources produces different colours which are coded as information bits. The disadvantage is that it increases the complexity of the transceivers.
4. Sub-Carrier Inverse PPM (SCIPPM): This method is
divided into two parts (1) sub-carrier part and (2) DC part. The DC part is used only for lighting or indicating. When there is no requirement for lighting or indicating, SCPPM (Sub-Carrier PPM) is used in order to save energy.
5. Frequency Shift Keying (FSK): In this method, data is
represented by varying the frequencies of the carrier signal. Before transmitting two distinct values (0 and 1), there needs to be two distinct frequencies.
6. SIM-OFDM (Sub-Carrier Index Modulation OFDM):
This is a new approach to transmission in which an additional dimension is added to conventional 2D amplitude/phase modulation (APM) techniques such as quadrature amplitude modulation (QAM) and amplitude shift keying (ASK). The key idea is to use the sub-carrier index to convey information to the receiver.
3.2 Usage Models
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 light‘s frequency with each frequency encoding a different data channel. Such advancements promise a theoretical speed of 10 Gbps – meaning one can download a full high- definition film in just 30 seconds
For giga-speed technologies, the Li-Fi Consortium defined Giga Dock, Giga Beam, Giga Shower, Giga Spot and Giga MIMO models to tackle different user scenarios for wireless indoor and indoor-like transfers of data. Giga Dock is a wireless docking solution that includes wireless charging for smart phones tablets or notebooks, with speeds up to 10 Gbps. Meanwhile, the Giga Beam model is a point-to-point data link for kiosk applications or portable-to-portable data exchanges. Thus a two-hour full HDTV movie (5 GB) can be transferred from one device to another within four seconds.
Fig-4 : Array of led
Giga Shower, Giga Spot and Giga-MIMO are the other in-house communication models. On one side, a transmitter or receiver is mounted into the ceiling connected to, say, a media server. On the other side are portable or fixed devices on a desk in an office, in an operating room, in a production hall or at an airport. Giga Shower provides unidirectional data services via many channels to multiple users with gigabit-class communication speed over several meters. This is like watching TV channels or listening to different radio stations where no uplink channel is needed. In case Giga Shower is used to sell books, music or movies, the connected media server can be accessed via Wi-Fi. To process payment through via mobile device. giga spot and giga shower MIMO are optical wireless single- and multi- channel Hot Spot solutions offering bidirectional gigabit-class communication in a room, hall or shopping mall for example
a. (b)
Fig-5: (a) Giga shower, (b) Giga spot
3.3 Implementation of Li-Fi:
The main components of a simple system based on Li-Fi are:
i. High brightness LED which acts as the communication
source
ii. Silicon photodiode which serves as the receiving
element
Data from the sender is converted into an intermediate data representation i.e. byte format and then converted into light signals which are emitted by the transmitter. The light signal is received by the photodiode at the receiver side. The reverse process takes place at the destination computer to retrieve the data back from the received light. LEDs are employed as the light sources. The model transmits digital signal by means of direct modulation of the light. The emitted light is detected by an optical receiver.
Source Computer: Data Reading Module F 0 E 0 Data Conversion
Module F 0 E 0 Transmitter Module
Destination Computer: Receiver Module F 0 E 0 Data Interpretation
Module F 0 E 0 Data Display (GUI)
The different components serve the following functions:
Data Conversion Module – converts data into bytes so that it can be represented as a digital signal. It can also encrypt the data before conversion.
Transmitter Module – generates the corresponding on-off pattern for the LEDs.
Receiver Module – has a photo diode to detect the on and off states of the LEDs. It captures this sequence and generates the binary sequence of the received signal
Data Interpretation Module – converts data into the original format. If encryption was done, it also performs decryption.
The Li-Fi Consortium provides the fastest wireless data transfer technology presently available. Our current solutions offer effective transmission rates of up to 10 Gbps, allowing a 2 hour HDTV film to be transferred in less than 30 seconds. This can be extended to several 100 Gbps in future versions
(vii) Smart Lighting
Street lamps can in the future be used to provide Li-Fi hotspots and can also be used to control and monitor lighting and data.
(viii) Mobile Connectivity
Laptops, tablets, smart phones and various other mobile devices can interconnect with each other using Li-Fi, much like they interconnect today using Wi-Fi. These short range links provide very high data rates as well as increased security.
(ix) Toys
Several toys consist of LED lights and these can be utilized to implement low-cost communication in order to build interactive toys.
(x) RF Spectrum Relief
Li-Fi networks can be used to relieve the radio spectrum off of excessive capacity demands of cellular networks.
(xi) RF Avoidance
Li-Fi can be used as a solution to any situation in which hypersensitivity to radio frequencies is a problem and radio waves cannot be used for communication or data transfer.
(xii) Indoor Wireless Communication
Li-Fi is very well suited for indoor wireless communication and data transmission. Li-Fi makes use of a free, unlicensed spectrum and is not affected by RF noise. Moreover, most indoor locations would have a sufficient amount of light sources and provide additional security since Li-Fi as previously discussed cannot penetrate through walls.
(xiii) Retail Analytics
Li-Fi can find wide application in retail analytics. Most retail stores consist of a rich lighting environment comprising of abundant sources of light which may be utilized for Li-Fi. Li-Fi could be used to track the behaviour of individual shoppers. Since most customers nowadays possess smartphones, Li-Fi could be used to connect to these smartphones to link up the people, product and purchasing, and thereby greatly simplify the overall shopping process.
(xiv) Casinos
Like retail stores, casinos also have rich lighting environments which could be easily harnessed for Li-Fi, which can find application in the large amount of video monitoring equipment that most casinos employ.
(xv) Hidden Communications
Li-Fi is extremely useful for applications in which communications must be hidden. These involve various military and defense-based communications as well as communications in hospitals.
(xvi) Line of Sight Applications
Li-Fi can also be used in situations where line of sight makes a difference, such as in vehicle to vehicle communication as previously discussed as well as in indoor GPS systems.
(xvii) Spatial Reuse
Li-Fi can act as an alternative in regions with high density wireless communication where 500 or more users may be contending for Wi-Fi. This would lead to low access speeds for the users. Li-Fi can be used to share some of the load of Wi-Fi.
V. CONCLUSION AND FUTURE SCOPE OF LI-FI
Li-Fi is still in its incipient stages and thus offers tremendous scope for future research and innovation. The following is a brief overview of some of the research work being conducted in the field and the future scope for this technology.
Researchers are developing micron sized LEDs which flicker on and off 1000 times faster than larger LEDs. They provide faster data transfer and also take up less space. Moreover, 1000 micron sized LEDs can fit into area required by 1 sq. mm large single LED. A 1 sq. mm sized array of micron sized LEDs could hence communicate 1000×1000 (i.e. a million) times as much information as a single 1mm LED. The Li-Fi Consortium asserts that it is possible to achieve speeds greater than 10Gbps. Researchers at the Heinrich Hertz Institute in Berlin, Germany, have achieved data rates of over 500 megabytes per second using a standard white-light LED.
Harald Haas’ group, with researchers from Universities of Oxford, Cambridge, Strathclyde and St. Andrews, are involved in a four-year, £5.8 million project funded by the Engineering and Physical Sciences Research Council. They are researching ultra-parallel VLC, which makes use of multiple colours to offer high-bandwidth linking over few meters. According to Haas, LEDs will evolve to more than just light sources and in the next 25 years, bulbs will have the processing power of modern cellphones. Illumination will only be one of its many purposes.
The Li-Fi Consortium recently demonstrated the use of red, green and blue LEDs as both emitters and photodiodes to detect light. They created a system that could send and receive data at rates of 110 Mbps. With unidirectional transmission, they achieved a rate of 155 Mbps. However, these speeds were achieved with regular LEDs. The Consortium has developed a
better LED which can provide data rates close to 4 Gbps while operating only on 5 milli-watts of optical output power and making use of high-bandwidth photodiodes at the receiving end. By enhancing the distance, using a simple lens, they can send data a distance of 10 meters at speeds of 1.1 Gbps. Mexican company Sisoft and researchers from the Autonomous Technological Institute of Mexico (ITAM) have developed a wireless technology that transmits data through light emitted from LED lamps while simultaneously lighting the room. The team started with audio and cabled up a protoboard table to a smartphone using the 3.5mm audio jack. The table converted the audio signal into a light signal transmitted by an emitter across the spectrum generated by an LED lamp. At the receiver, a receptor in a speaker captured the signal and converted it back to the original audio signal that was then played by the speaker. The principle is similar for wireless internet transmission but it makes use of a receptor designed to be placed above a router. The router contains an LED lamp for transmitting data so that anyone within the halo of the light emitted by the LED will be in transmission range. Sisoft claims to have used this technology to transmit data at 10 Gbps.
More recently, researchers at the University of Oxford employed Li-Fi to attain bi-directional speeds of 224 Gbps. These speeds would allow 18 movies (1.5 GB each) to be downloaded in a single second. The research used specialized broadcast LEDs and receivers which operated with different fields of view as well as bands that impact the data rates. The link operates over a range of about 3 meters at 224 Gbps and 112 Gbps with a wide field of view of 60° and 36° respectively, thereby offering practical room-scale coverage. These speeds far exceed the speeds offered by modern Wi-Fi (about 600 Mbps).
Li-Fi technology thus offers numerous benefits but there are certain barriers that must be overcome before it becomes a ubiquitous part of our lives. Criticisms of Li-Fi include complaints that it cannot work in the dark or if it is raining or foggy, that it is not built into modern computers and questions as to why people should switch to Li-Fi when Wi-Fi could perform similar tasks. However any new technology faces criticisms when first introduced and it will take time before Li-Fi gains broad acceptance. That being said, presently there are many international developers of VLC technologies including Intel, Siemens, CASIO, VLCC, Philips, Fraunhofer, Samsung, ByteLight and the Li-Fi Consortium. TIME magazine has also named Li-Fi as one of the 50 best inventions of 2011. Li-Fi could ultimately lead to the Internet of Things i.e. all electronic devices being connected to the Internet, with the LEDs on the electronics being used as Internet access points. The Li-Fi market is projected to have an annual growth rate of 82% from 2013 to 2018 and to be worth over $6 billion per year by 2018.
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