Light Fidelity (Li-Fi) is a bidirectional, high-speed and fully networked wireless communication technology similar to Wi-Fi. The term was coined by Harald Haas[1] 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.[2]
Technology details[edit]
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.[3] 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.[4]
Visible light communications (VLC) works by switching the current to the LEDs off and on at a very high rate,[5] 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.[6] The light waves cannot penetrate walls which makes a much shorter range, though more secure from hacking, relative to Wi-Fi.[7][8] Direct line of sight is not necessary for Li-Fi to transmit a signal; light reflected off the walls can achieve 70 Mbit/s.[9][10]
Li-Fi has the advantage of being useful in electromagnetic sensitive areas such as in aircraft cabins, hospitals and nuclear power plants without causing electromagnetic interference.[7][11][8] 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.[12] The visible light spectrum is 10,000 times larger than the entire radio frequency spectrum.[13] Researchers have reached data rates of over 224 Gbit/s, which is much faster than typical fast broadband in 2013.[14][15] Li-Fi is expected to be ten times cheaper than Wi-Fi.[6] Short range, low reliability and high installation costs are the potential downsides.[4][5]
PureLiFi demonstrated the first commercially available Li-Fi system, the Li-1st, at the 2014 Mobile World Congress in Barcelona.[16]
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.[17][18]
History[edit]
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.[20]
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.[21] Haas promoted this technology in his 2011 TED Global talk and helped start a company to market it.[22] PureLiFi, formerly pureVLC, is an original equipment manufacturer (OEM) firm set up to commercialize Li-Fi products for integration with existing LED-lighting systems.[23][24]
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.[25]
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.[26]
VLC technology was exhibited in 2012 using Li-Fi.[27] By August 2013, data rates of over 1.6 Gbit/s were demonstrated over a single color LED.[28] In September 2013, a press release said that Li-Fi, or VLC systems in general, do not require line-of-sight conditions.[29] In October 2013, it was reported Chinese manufacturers were working on Li-Fi development kits.[30]
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.[31] 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.[32]
Recent integrated CMOS optical receivers for Li-Fi systems are implemented with avalanche photodiodes (APDs) which has a low sensitivity. [33] In July 2015, IEEE has operated the APD in Geiger-mode as a single photon avalanche diode (SPAD) to increase the efficiency of energy-usage and makes the receiver more sensitive. [34] Also this operation could be performed as quantum-limited sensitivity that makes receivers detect weak signals from far distance. [33]
Commercialization[edit]
There are some startup companies around the world working on LiFi technology. Visible Light Communication (VLC) is another term that is sometimes used for this technology. Here is the list of companies developing LiFi technology:
PureLiFi is the main company in this field. They are developing LiFi luminaries with a French company named Lucibel.
The main startup company in US working on this technology is VLNComm. They have been funded by US Department of Energy and National Science Foundation.
OLEDComm is a French company working on LiFi. They have some products for indoor positioning.
LightPointe is a manufacturer of point-to-point Gigabit Ethernet Free Space Optics and Hybrid Optical-Radio Bridges, has recently started working on VLC.
i2cat, located in Barcelona, Spain is also working on location based system using visible light communication.
ByteLight which is recently acquired by the LED manufacturer Acuty Brands is developing location based services.
Nakagawa Lab in Japan
Basic6
Velmenni
Zero1
Axrtek
There are many big companies entertaining this technology: Qualcomm, GE, Panasonic, Philips, Samsung, OSRAM
Standards[edit]
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 wider bandwidth.
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.[35] 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.[citation needed]
The standard defines three PHY layers with different rates:
The PHY 1 was established for outdoor application and works from 11.67 kbit/s to 267.6 kbit/s.
The PHY 2 layer permits reaching data rates from 1.25 Mbit/s to 96 Mbit/s.
The PHY 3 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.[36]
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.[citation needed]
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.[37][38] 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. The first smartphones using this technology should arrive in 2015. This screen can also receive VLC signals as well as the smartphone camera.[39] The cost of these screens per smartphone is between $2 and $3, much cheaper than most new technology.[40]
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.[41]
Home & Building Automation[edit]
It is predicted that future home & building automation [42] will be highly dependent on the Li-Fi technology for being secure & fast. As the light cannot penetrate through walls hence the signal cannot be hacked from a remote location.
Applications[edit]
Security[edit]
In contrast to radio frequency waves used by Wi-Fi, lights cannot penetrate through walls and doors. In a meeting or living room condition, with some prevention on transparent materials, like curtains on window, the access of a Li-Fi channel is constrained in that room.[43]
Underwater Application[edit]
Most remotely underwater operated vehicles (ROVs) use cables to transmit command, but the length of cables then limits the area ROVs can detect. However, as light wave could travel through water, Li-Fi could be implemented on vehicles to receive and send back signals. [44]
While it is theoretically possible for Li-Fi to be used in underwater applications, its utility is limited by the distance light can penetrate water. Significant amounts of light do not penetrate further than 200 meters. Past 1000 meters, no light penetrates.[45]
Hospital[edit]
Many treatments now involve multiple individuals, Li-Fi system could be a better system to transmit communication about the information of patients. [46] Besides providing a higher speed, light waves also have little effect on medical instruments and human bodies. [47]
Vehicles[edit]
Vehicles could communicate with one another via front and back lights to increase road safety. Also street lamps and traffic signals could also provide information about current road situations.[48]
Li fi technology - A complete overview
1. CONTENTS Present Scenario Introduction Basic Concepts How Li-Fi Works? Li-Fi Construction Comparisons Advantages Limitations Solutions to problems Conclusion
2. Wireless data is growing exponentially… YouTube In 2011, ~ 140 views for every person on earth (over 1 Trillion views) 72 hours of video are uploaded to YouTube every minute 25% of global YouTube views come from mobile devices Internet video traffic is growing at 48% CAGR
3. …leading to RF Spectrum Shortage
4. Present Scenario 1.4 Million 5 Billion Radio Spectrum is congested but the demand for wireless data double each year .Every thing, it seems want to use wireless data but the capacity is drying up.
5. How to fix the problem? Identify new spectrum, or Enhance spectrum reuse (smaller cells), or Both measures jointly
6. Introduction Li-Fi is a VLC, visible light communication, technology developed by a team of scientists including Dr. Gordon Povey, Prof. Harald Haas and Dr. Mostafa Afgani at the university of Edinburgh. Li-Fi is now part of the Visible Light Communication (VLC) PAN IEEE 802.15.7 standard. “Li-Fi” is typically implemented using white LED light bulbs. LI-FI is transmission of data through illumination ,sending data through a LED light bulb that varies in intensity faster than human eye can follow.
7. Why only VLC ?
8. Basic Concepts LED i.e. Light emitting diode can be switched on and off faster since operating speed of LED 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: switching on and LED is a logical ‘1’, switching it off is 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.
9. How Li-Fi Works?
10. Li-Fi Construction Fig. : LIFI Block Diagram The LI FI product consists of 4 primary sub-assemblies: • Bulb • RF power amplifier circuit (PA) • Printed circuit board (PCB) • Enclosure
11. Comparison with Wi-Fi
12. Advantages Capacity Availability Efficiency Easy To Use Fast Data Transfer Harmlessness Low-cost
13. Limitations/Challenges Light can't pass through solid objects, and thus the signal may be lost Connectivity while moving Multiuser support Dimming Shadowing
14. Solutions to Challenging problems Solution for connectivity The solution is called “handover”, using which the user is transferred from one BS to another Handover is done in the area that two BS’s have common coverage The user can be transferred from one light source to another in the area that is under the coverage of both
15. Contd.. Solution for multiuser support One solution is time division multiplexing (TDM) Each frame is divided into equal time slots Each user transmit data in one time slot in a predefined order The other solution is code division multiple access (CDMA) Codes are assigned to users Each user transmit its data using the assigned signature pattern It is used in 3G and 4G cellular networks
16. Contd.. Solution for shadowing As shown before, the impulse response in VLC systems has two parts When the line-of-sight (LOS) part (which is received via direct path) is blocked, the impulse response is only the second part Then the data can be recovered using the second part which is indeed the received data from the indirect paths (multipath signal)
17. Conclusion Li-Fi will make are lives more technology driven in the near future. With its magic of light it can make our world a greener, safer, cleaner and moreover a brighter place to live.
18. References http://en.wikipedia.org/wiki/Li-Fi http://teleinfobd.blogspot.in/2012/01/what-is-lifi.html technopits.blogspot.comtechnology.cgap.org/2012/01/ 11/a-lifi world/ www.lificonsortium.org/ the-gadgeteer.com/2011/08/29/li-fi-internet-at-the-speed-oflight/ http://www.digplanet.com/wiki/Li-Fi Visible-light communication: Tripping the light fantastic: A fast and cheap optical version of Wi-Fi is coming”, Economist, dated 28Jan 2012
19. Thank You All
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