Light Fidelity (Li-Fi):

Li-Fi  is a bidirectional, high-speed and fully networked wireless communication technology similar to Wi-Fi. The term was coined by Harald Haas and is a form of visible light communication and a subset of optical wireless communications (OWC) and could be a complement to RF communication (Wi-Fi or cellular networks), or even a replacement in contexts of data broadcasting.

It is wire and uv visible-light communication or infrared and near-ultraviolet instead of radio-frequency spectrum, part of optical wireless communications technology, which carries much more information, and has been proposed as a solution to the RF-bandwidth limitations.

LiFi is the use of the visible light portion of the electromagnetic spectrum to transmit information at very high speeds. This is in contrast to established forms of wireless communication such as Wi-Fi which use traditional radio frequency (RF) signals to transmit data.

Contents:

·         1.Technology details

·         2.History

·         3.Standards

·         4.Working of Li-fi Technology

·         5.Reasons to promote Li-Fi Technology

·         6. Advantages and challenges of Li-Fi

·         7. Difference between Li-Fi and Wi-Fi

Technology Details:

This OWC technology uses light from light-emitting diodes (LEDs) as a medium to deliver networked, mobile, high-speed communication in a similar manner to Wi-Fi. The Li-Fi market is projected to have a compound annual growth rate of 82% from 2013 to 2018 and to be worth over $6 billion per year by 2018.

Visible light communications (VLC) works by switching the current to the LEDs off and on at a very high rate, too quick to be noticed by the human eye. Although Li-Fi LEDs would have to be kept on to transmit data, they could be dimmed to below human visibility while still emitting enough light to carry data. The light waves cannot penetrate walls which makes a much shorter range, though more secure from hacking, relative to Wi-Fi. Direct line of sight is not necessary for Li-Fi to transmit a signal; light reflected off the walls can achieve 70 Mbit/s.

Li-Fi has the advantage of being useful in electromagnetic sensitive areas such as in aircraft cabins, hospitals and nuclear power plants without causingelectromagnetic interference. Both Wi-Fi and Li-Fi transmit data over the electromagnetic spectrum, but whereas Wi-Fi utilizes radio waves, Li-Fi uses visible light. While the US Federal Communications Commission has warned of a potential spectrum crisis because Wi-Fi is close to full capacity, Li-Fi has almost no limitations on capacity. The visible light spectrum is 10,000 times larger than the entire radio frequency spectrum. Researchers have reached data rates of over 10 Gbit/s, which is much faster than typical fast broadband in 2013. Li-Fi is expected to be ten times cheaper than Wi-Fi. Short range, low reliability and high installation costs are the potential downsides.

PureLiFi demonstrated the first commercially available Li-Fi system, the Li-1st, at the 2014 Mobile World Congress in Barcelona.

Bg-Fi is a Li-Fi system consisting of an application for a mobile device, and a simple consumer product, like an IoT (Internet of Things) device, with color sensor, microcontroller, and embedded software. Light from the mobile device display communicates to the color sensor on the consumer product, which converts the light into digital information. Light emitting diodes enable the consumer product to communicate synchronously with the mobile device.

History:

Harald Haas, coined the term "Li-Fi" at his TED Global Talk where he introduced the idea of "Wireless data from every light".^[19] He is Chairman of Mobile Communications at the University of Edinburgh and co-founder of pureLiFi.

The general term visible light communication (VLC), whose history dates back to the 1880s, includes any use of the visible light portion of the electromagnetic spectrum to transmit information. The D-Light project at Edinburgh's Institute for Digital Communications was funded from January 2010 to January 2012. Haas promoted this technology in his 2011 TED Global talk and helped start a company to market it. PureLiFi, formerly pureVLC, is an original equipment manufacturer(OEM) firm set up to commercialize Li-Fi products for integration with existing LED-lighting systems.

In October 2011, 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.

A number of companies offer uni-directional VLC products, which is not the same as Li-Fi - a term defined by the IEEE 802.15.7r1 standardization committee.

VLC technology was exhibited in 2012 using Li-Fi. By August 2013, data rates of over 1.6 Gbit/s were demonstrated over a single color LED. In September 2013, a press release said that Li-Fi, or VLC systems in general, do not require line-of-sight conditions. In October 2013, it was reported Chinese manufacturers were working on Li-Fi development kits.

In April 2014, the Russian company Stins Coman announced the development of a Li-Fi wireless local network called BeamCaster. Their current module transfers data at 1.25 gigabytes per second but they foresee boosting speeds up to 5 GB/second in the near future. In 2014 a new record was established by Sisoft (a Mexican company) that was able to transfer data at speeds of up to 10 Gbit/s across a light spectrum emitted by LED lamps.

Standards:

Like Wi-Fi, Li-Fi is wireless and uses similar 802.11 protocols; but it uses visible light communication (instead of radio frequency waves), which has much widerbandwidth.

One part of VLC is modeled after communication protocols established by the IEEE 802 workgroup. However, the IEEE 802.15.7 standard is out-of-date, it fails to consider the latest technological developments in the field of optical wireless communications, specifically with the introduction of optical orthogonal frequency-division multiplexing (O-OFDM) modulation methods which have been optimized for data rates, multiple-access and energy efficiency. The introduction of O-OFDM means that a new drive for standardization of optical wireless communications is required.

Nonetheless, the IEEE 802.15.7 standard defines the physical layer (PHY) and media access control (MAC) layer. The standard is able to deliver enough data rates to transmit audio, video and multimedia services. It takes into account optical transmission mobility, its compatibility with artificial lighting present in infrastructures, and the interference which may be generated by ambient lighting. The MAC layer permits using the link with the other layers as with the TCP/IP protocol.

The standard defines three PHY layers with different rates:

·         The PHY I was established for outdoor application and works from 11.67 kbit/s to 267.6 kbit/s.

·         The PHY II layer permits reaching data rates from 1.25 Mbit/s to 96 Mbit/s.

·         The PHY III is used for many emissions sources with a particular modulation method called color shift keying (CSK). PHY III can deliver rates from 12 Mbit/s to 96 Mbit/s.

The modulation formats recognized for PHY I and PHY II are on-off keying (OOK) and variable pulse position modulation (VPPM). The Manchester coding used for the PHY I and PHY II layers includes the clock inside the transmitted data by representing a logic 0 with an OOK symbol "01" and a logic 1 with an OOK symbol "10", all with a DC component. The DC component avoids light extinction in case of an extended run of logic 0's.

The first VLC smartphone prototype was presented at the Consumer Electronics Show in Las Vegas from January 7–10 in 2014. The phone uses SunPartner's Wysips CONNECT, a technique that converts light waves into usable energy, making the phone capable of receiving and decoding signals without drawing on its battery. A clear thin layer of crystal glass can be added to small screens like watches and smartphones that make them solar powered. Smartphones could gain 15% more battery life during a typical day. This first smartphones using this technology should arrive in 2015. This screen can also receive VLC signals as well as the smartphone camera. The cost of these screens per smartphone is between $2 and $3, much cheaper than most new technology.

Philips lighting company has developed a VLC system for shoppers at stores. They have to download an app on their smartphone and then their smartphone works with the LEDs in the store. The LEDs can pinpoint where they are located in the store and give them corresponding coupons and information based on which aisle they are on and what they are looking at.

Working of Li-Fi Technology:

Li-Fi and Wi-Fi are quite similar as both transmit data electromagnetically. However, Wi-Fi uses radio waves while Li-Fi runs on visible light.

As we now know, Li-Fi is a Visible Light Communications (VLC) system. This means that it accommodates a photo-detector to receive light signals and a signal processing element to convert the data into 'stream-able' content.

An LED lightbulb is a semi-conductor light source meaning that the constant current of electricity supplied to an LED lightbulb can be dipped and dimmed, up and down at extremely high speeds, without being visible to the human eye.

For example, data is fed into an LED light bulb (with signal processing technology), it then sends data (embedded in its beam) at rapid speeds to the photo-detector (photodiode).

The tiny changes in the rapid dimming of LED bulbs is then converted by the 'receiver' into electrical signal.

The signal is then converted back into a binary data stream that we would recognise as web, video and audio applications that run on internet enables devices. 

The functioning of new Li-Fi technology is just simple. You will have a light source at one end like a LED and a photo detector (Light Sensor) on the other end.

As soon as, LED starts glowing, photo detector or light sensor on other end will detect light and get a binary 1 otherwise binary 0.  How can data be transmit via this new Li-F- technology?

Flashing a LED certain times will build up a message to transmit. Flashing of light is detected by the photo detector or light sensor and it will receive a message.

Now, think of several LEDs with some different colors, flashing together and building a huge information to transmit. It is observed that green laser with the red laser can transmit data at 1 GBPS.

Reasons to Promote Li-Fi Technologies:

A Li-Fi lthough the use of light in order to transmit data can be limited in comparison to radio waves, there is a great amount of possibilities that can be developed due to this technology. In essence, a single pixel of a monitor could transmit a single channel of information to a source. Although this technology is still in its infant stages, the usefulness of this Li-Fi technology has implications for a great amount of good.

1.    Distance - The sheer range of transmitting information could be worth the decrease in data speeds. The RONJA project in the Czech Republic can transmit a 10 Mbit/s Ethernet-type link just under a mile. As developments of this aspect continue, the range could be entirely up to the strength of the light which is emitting the information. Although the speeds are less than what they are for gigabit Ethernet, the power of the beam can allow DVD-quality streaming of video to any location connected to the Li-Fi device.

2.    Cost - Instead of running close to a mile worth of cable, the LED-powered Li-Fi connection could be used to beam the information directly to the destination. Using a point-to-point array, office buildings can stay connected to each other without the use of additional cables being laid from one access point to another. The only problem the two buildings would be faced with is obstruction by solid objects or dense weather patterns such as heavy fog or snow.

3.    Traffic Updates - Could you imagine having a car that uses a GPS system that receives information from traffic lights informing you of accidents and/or delays up ahead? There is a kind of system like that already in play for GPS navigational systems, but the traffic lights could be updating drivers using basic information or streaming video directly from news broadcasts.

4.    Game Consoles - An innovative idea would be to put sensors on a television in order to receive information from game consoles. This would allow the unit to be place literally anywhere within the room as long as there is a direct line of sight to the sensor. Could you imagine a game system like the Xbox using a Kinect and all of it being completely wireless except for the power going into the unit? That will be tackled once wireless energy is perfected for practical home use.

5.    Television Interaction - Instead of using apps or additional installations, you could theoretically hold your phone up as you sit on the couch and have every piece of information regarding the show or movie you are currently watching sent to your display – even recording directly to your mobile device. Of course, this may spawn some kind of copyright lawsuit because you are illegally copying a movie or television show, but you still get the idea. There are a number of reasons why investing in Li-Fi technology can have a great benefit to the future of wireless networking. Although there are a few aspects that need to be ironed out before it can be introduced on a wide scale of practicality, the future looks to be very promising. Even if the technology was merely developed as a small scale indoor application to “beam” information directly to a computer system without the use of Ethernet cable being strewn about the floor, visible-light communications could set the benchmark higher for wireless transmissions.

Advantages and challenges of Li-Fi Technology:

Best advantage of Li-Fi Technology will be accessing internet at high speed in those areas where optical fires are not easy to install. Many times while setting up a wi-fi route, you need to choose a specific spot to place your router so that on an average, it provides good connectivity in all your rooms.

If, all lights in your rooms will communicate each other and creates a bridge of wireless networks  to provide internet access. Then Li-Fi technology  would be the best optimum solution over Wi-Fi technology. Li-Fi technology can also be used to extend wireless networks at your home, office or university.

Li-Fi Technology can also be used to control traffic conditions by placing this new technology into the LEDs of cars. It can also be used with overhead lights of airplanes.

Besides these advantages, Li-Fi technology has several challenges to face. Li-Fi technology is requires a prefect line-of-sight to transmit data. Other major challenge to face by this new Li-Fi technology is, how optimally data can be transferred back to the transmitter.

LiFi vs WiFi-Basic difference between LiFi and WiFi:

                WiFi technologies.While some may think that Li-Fi with its 224 gigabits per secondleaves Wi-Fi in the dust, Li-Fi's exclusive use of visible light could halt a mass uptake. 

Li-Fi signals cannot pass through walls, so in order to enjoy full connectivity, capable LED bulbs will need to be placed throughout the home. Not to mention, Li-Fi requires the lightbulb is on at all times to provide connectivity, meaning that the lights will need to be on during the day.

What's more, where there is a lack of lightbulbs, there is a lack of Li-Fi internet so Li-Fi does take a hit when it comes to public Wi-Fi networks.

In an announcement yesterday, an extension of standard Wi-Fi is coming and it's called Wi-Fi HaLow.

This new project claims to double the range of connectivity while using less power. Due to this, Wi-Fi HaLow is reportedly perfect for battery powered devices such as smartwatches, smartphones and lends itself to Internet of Things devices such as sensors and smart applications. 

But it's not all doom and gloom! Due to its impressive speeds, Li-Fi could make a huge impact on the internet of things too, with data transferred at much higher levels with even more devices able to connect to one another. (See also: What is the Internet of Things?)

                What's more, due to its shorter range, Li-Fi is more secure than Wi-Fi and it's reported that embedded light beams reflected off a surface could still achieve

Following table mentions feature comparison between both:

Feature	LiFi	WiFi
Full form	Light Fidelity	Wireless Fidelity
Operation	LiFi transmits data using light with the help of LED bulbs.	WiFi transmits data using radio waves with the help of WiFi router.
Interference	Do not have any intereference issues similar to radio frequency waves.	Will have intereference issues from nearby access  points(routers)
Technology	Present IrDA compliant devices	WLAN 802.11a/b/g/n/ac/ad standard compliant devices
Applications	Used in airlines, undersea explorations, operation theaters in the hospitals, office and home premises for data transfer and internet browsing	Used for internet browsing with the help of wifi kiosks  or wifi hotspots
Merits(advantages)	Interference is less, can pass through salty sea water, works in densy region	Interference is more, can not pass through sea water,  works in less densy region
Privacy	In LiFi, light is blocked by the walls and hence will provide more secure data transfer	In WiFi, RF signal can not be blocked by the walls  and hence need to employ techniques to achieve  secure data transfer.
Data transfer speed	About 1 Gbps	WLAN-11n offers 150Mbps, About 1-2 Gbps can  be achieved using WiGig/Giga-IR
Frequency of operation	10 thousand times frequency spectrum of the radio	2.4GHz, 4.9GHz and 5GHz
Data density	Works in high dense environment	Works in less dense environment due to interference related issues
Coverage distance	About 10 meters	About 32 meters (WLAN 802.11b/11g), vary based on  transmit power and antenna type
System components	Lamp driver, LED bulb(lamp) and photo detector will make up complete LiFi system.	Requires routers to be installed, subscriber devices (laptops,PDAs,desktops) are referred as stations

Lifi is not the replacement of wifi technology. It can be considered as incredible companion of the wifi technology. It operates between 380 nm to 780 nm optical range. LiFi is used to exchange data incredibly rapidly and securely at much lower power level compare to WiFi.