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Visible light Communications or LiFi for, Internet of Things, Vehicular networks, Machine-to-Machine communication, 5G mobile and Underwater networks

It is predicted that LEDs will be the ultimate light source in the near future powering indoor illumination, outdoor lamps, traffic signs, advertising displays, car headlights/taillights, etc. Li-Fi, or light fidelity, promises to double their utility of light-emitting diodes (LEDs) by using their light as a medium to deliver networked, mobile, high-speed communication in a similar manner as Wi-Fi. Li-Fi has already achieved blistering speeds in the lab. Researchers at the University of Oxford have reached a new milestone in networking by using light fidelity (Li-Fi) to achieve bi-directional speeds of 224 gigabits per second (Gbps).

And now, scientists have taken Li-Fi out of the lab for the first time, trialling it in offices and industrial environments in Tallinn, Estonia, reporting that they can achieve data transmission at 1 GB per second – that’s 100 times faster than current average Wi-Fi speeds.

In future LiFi would make possible the extensive deployment of visible light communication for a wide range of short and medium-range communication applications including wireless, local, personal, and body area networks (WLAN, WPAN, and WBANs), vehicular networks, underwater networks and machine-to-machine (M2M) communication among others.

It works by switching LEDs on and off within nanoseconds to communicate data, which is too quick to be noticed by the human eye. The dual use of LEDs for illumination and communication purposes is a sustainable and energy-efficient approach and has the potential to revolutionize how we use light. Haas said. “In the future we will not only have 14 billion light bulbs, we may have 14 billion Li-Fis deployed worldwide for a cleaner, greener, and even brighter future.”

LiFi has started entering into mainstream. Dubai plans soon be the first city to fit its street lights with Li-Fi. The lamps are said to have cost Dubai $1000 each. Li-Fi is reportedly being tested in Dubai, by UAE-based telecommunications provider, du and Zero1. Du claims to have successfully provided internet, audio and video streaming over a Li-Fi connection.

Li-Fi pioneers pureLiFi already have two products on the market: Li-Flame Ceiling Unit to connect to an LED light fixture and Li-Flame Desktop Unit which connects to a device via USB, both aiming to provide light and connectivity in one device. What’s more, reports suggest that Apple may build future iPhones with Li-Fi capabilities.

Short range, low reliability and high installation costs are the potential downsides of LiFi. Researchers are now making efforts towards developing heterogeneous networks incorporating both WiFi and LiFi to make the best of the pros of both VLC and WiFi.  Operators say that 80% of the mobile traffic occurs indoors; therefore, the combination of LiFi and WiFi has great potential to be breakthrough technologies in future HetNets including the next generation (5G) mobile telecommunications systems

 

Light Fidelity or Li Fi

An LED lightbulb is a semi-conductor light source; this essentially means 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.

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 more than 250 times faster than superfast broadband. Li-Fi is expected to be ten times cheaper than Wi-Fi. The LED lights require so little energy; they can be powered by a standard ethernet cord. Inventor Harald Haas has also suggested that the smart lights could be powered by solar cells charging batteries.

Li-Fi emits no electromagnetic interference and so does not interfere with medical instruments, nor is it interfered with by MRI scanners. Thus, they can be used in electromagnetic sensitive areas such as in aircraft cabins, hospitals and nuclear power plants without causing electromagnetic interference.

Li-Fi could lead to the Internet of Things, which is everything electronic being connected to the internet, with the LED lights on the electronics being used as Li-Fi internet access points.

LEDs are also being widely used in outdoor lighting, traffic signs, advertising displays, car headlights/taillights, etc. Vehicles fitted with LED-based front and back lights can communicate with each other and with the road side infrastructure (RSI), i.e., street lamps, traffic lights, through the VLC technology.

Furthermore, LED-based RSI can be used for both signaling and broadcasting safety-related information to vehicles on the road. VLC is well positioned to address both the low latency required in safety functionalities (i.e., emergency electronic brake lights, intersection collision warning, in-vehicle signage, platooning) and high speeds required in so-called infotainment applications (i.e., map downloads and updates, media downloading, point of interest notification, high-speed internet access, multiplayer gaming, and cooperative downloading), according to Murat Uysal and Hatef Nouri, Ozyegin University, Turkey

 

LiFi internet breakthrough: 224Gbps connection broadcast with an LED bulb

Li-Fi has already achieved blistering speeds in the lab. Researchers at the University of Oxford have reached a new milestone in networking by using light fidelity (Li-Fi) to achieve bi-directional speeds of 224 gigabits per second (Gbps). The 224Gbps speed would technically allow for 18 movies of 1.5GB each to be downloaded in a single second.

“The link operates over ~3 m range at 224 Gb/s (6 x 37.4 Gb/s) and 112 Gb/s (3 x 37.4 Gb/s) with a wide field of view (FOV) of 60° and 36°, respectively. To the best of our knowledge, this is the first demonstration of a wireless link of this type with a FOV that offers practical room-scale coverage,” the report states.

Although Li-Fi has faster speeds than Wi-Fi, it has a very short range. Over longer distances, using LEDs originally intended for lighting, and in otherwise more realistic conditions, Li-Fi is slower than the speeds achieved in the lab. Anagnostis Paraskevopoulos and colleagues at the Heinrich Hertz Institute in Germany, for instance, managed to achieve data transmission ratesup to 500 megabits per second over distances of one to two meters and transmission rates up to 100 megabits per second over 20 meters.

 

China makes breakthrough in Li-Fi technology, with speed of 50 Gbps

A test conducted by the Ministry of Industry and Information Technology confirmed that the real-time traffic rate of a Chinese VLC system had reached 50 gigabytes per second (Gbps), the ministry announced Friday, has been reported by Xinhua.

IT expert and academic Wu Jiangxing said it will be possible to establish a huge VLC network based on the billions of bulbs and LED lighting facilities already around the globe.

“Every bulb can serve as a high-speed Internet access point (similar to a WIFI hotspot) after VLC technology is widely applied in the future,” said Wu, unable to give a specific time frame. “Imagine downloading several movies while you are waiting for a green light at a crossroad or surfing the Internet on planes and high-speed trains via the lights.”

The VLC system was developed by the People’s Liberation Army (PLA) Information Engineering University and has entered a phase of “integration and micromation in design.” The university succeeded in developing a wireless broadcasting system based on VLC in 2013.

LiFi based networking

But while point-to-point demonstrations have proven LiFi to be a serious alternative to RF-based communications, the technology’s real strength lies in networking. Detector-receiver arrays also house infrared diodes to provide an uplink connection back to the LED-based LiFi access point.

And by combining numerous micro-LED transmitters and receiver assemblies, the researchers can take LiFi beyond a straightforward point-to-point communications system, and create a multiple-input multiple-output (MIMO) transmission network. Transmitters and receivers can even be combined in a single unit to create a single-input, single-output link.

As Haas emphasizes: “The LiFi communications system can serve many users. It allows multi-user access, has an uplink and downlink, and allows handover.”

“The coverage of each LED lamp is up to 10 square meters and when you leave that space, you are illuminated by another lamp, handover takes place, and you don’t lose wireless connectivity,” he adds.

Haas is also confident ambient light will not interfere with transmissions as the receivers are only sensitive to the modulating LED light.

“Even the 100 Hz flicker from an incandescent light bulb is not an issue, as our modulation frequency starts at 1 MHz,” he says. “As long as fluctuations are outside our modulation, these aren’t an issue.”

Smart LED Bulbs Deliver Communication and Illumination

Researchers at Disney Research and ETH Zurich designed and implemented the system called EnLighting, that enables distributed and fully connected LED light bulbs to communicate through free space optics to interconnect devices within a room.  The researchers added a system-on-a-chip (SoC) running an embedded version of Linux to each bulb, as well as photodiodes to enable sensing of incoming signals and an additional power supply for the added electronics.

“LED light bulbs mounted on the ceiling or in free-standing floor lamps easily cover a room, serving as illumination while at the same time creating a room-area network that allows data exchange between light-emitting devices,” said Markus Gross, vice president at Disney Research, adding that even if the bulb is switched off, it can still serve as a receiver of signals from those devices.

“Interconnecting appliances, sensors and a wide variety of devices into the Internet of Things has many potential benefits, but using radio links to do so threatens to make the radio spectrum an even scarcer resource,” said Gross. “Visible light communication networks conserve the radio spectrum, while also making it difficult to eavesdrop for anyone out of line of sight of the network.”

Optical wireless communication (OWC) uses infrared, visible or ultraviolet bands to enable wireless connectivity. With its powerful features such as high bandwidth, low cost and operation in an unregulated spectrum, OWC can be, in some applications, a powerful alternative to and, in others, complementary to the existing wireless technologies. OWC systems operating in the visible band (390-750 nm) are commonly referred to as visible light communication (VLC).

Ultra-parallel visible light communications (UP-VLC)

Harald Haas from University of Edinburgh, along with researchers from the Universities of -Cambridge, Oxford, St. Andrews, and Strathclyde are pursuing ultra-parallel visible light communication, which would use multiple colors of light to provide high-bandwidth linkages over distances of a few meters. In the lab, as part of the Ultra-Parallel Visible Light Communications Project (UP-VLC), Haas and colleagues have reached blisteringly fast 10Gbit/s data transmission speeds.

Here they developed micro-LED arrays to transmit 3.5Gbit/s via each red, green and blue micro-LEDs in parallel. They also applied novel spatial modulation orthogonal frequency divisional multiplexing so the micro-LED elements within the array could beam thousands of streams of light in parallel, multiplying the volume of data transmitted at any one time, reports Rebecca Pool in SPIE.

Yet many commercial LEDs use a phosphor coating to convert blue light to white light, and this coating limits how fast the devices can be modulated, slowing down data rates. Haas isn’t fazed, saying: “Even with slow, phosphor-coated LEDs, we can exploit parallelism in the spatial dimension.”

“Laser LEDs have bandwidths up to 1 GHz, as opposed to 20 MHz for the phosphor-coated LEDs, so we can also encode data in the frequency domain to achieve fast data rates,” he says.

“LEDs have been the bottleneck in data rate so as part of this project, we wanted to develop a technology that would unlock the vast amount of data rates available in the visible light spectrum,” says Haas. “We’ve achieved 10Gbit/s with these LEDs, but can reach 100Gbit/s using red, green and blue laser diodes.”

Haas’s team has also created the first receiver chip for Li-Fi with integrated avalanche photodiodes on CMOS. The 7.8-square-millimeter IC houses 49 photodiodes. In an avalanche photodiode, a single photon striking the receiver produces a cascade of electrons, amplifying the signal.

According to Haas, a detector-receiver array may have direct line of sight with a LED transmitter, but will also receive “residual” light that has reflected off surrounding walls, objects, the ground and ceiling. “If you block the strongest incoming ray, residual light still reaches the receiver, and a good photodetector on the receiver side will still make sense out of the weakest of signals,” he says.

“We can achieve the sensitivity we need with off-the-shelf avalanche photodiodes and PIN diodes, but colleagues at Edinburgh have pioneered single-photon avalanche diodes,” he adds. “These detect single photons, achieving sensitivities that are orders of magnitude higher than those from off-the-shelf avalanche photodiodes.”

“Recently, by integrating CMOS electronics with GaN based micro-LEDs, we have developed CMOS-controlled color-tunable smart displays. The color-tunable LED pixels in these displays have a modulation bandwidth of 100 MHz, thus providing simultaneously a wavelength-agile source for high-speed visible light communications.”

The vision is built on the unique capabilities of gallium nitride (GaN) optoelectronics to combine optical communications with lighting functions, and especially on the capability to implement new forms of spatial multiplexing, where individual elements in high-density arrays of GaN based light emitting diodes (LEDs) provide independent communications channels, but can combine as displays.

“We envisage ultra-high data density – potentially Tb/s/mm2 – arrays of LEDs driven via CMOS control electronics in novel addressing and encoding schemes and in compact and versatile forms.”

The emergence of VLC is in fact a result of recent development in solid state lighting technologies. New generations of LEDs have attractive features such as a long life expectancy, high tolerance to humidity, lower power consumption and reduced heat dissipation.

 

ASU’s white laser technology one of year’s top breakthroughs

Arizona State University electrical engineering professor Cun-Zheng Ning and his team have invented world’s first white laser, which could revolutionize communications, lighting and displays, is being recognized as one of the top 100 breakthroughs of the year by Popular Science magazine.

Their Nano photonics device is based on nanoscale materials, semiconductor that produces the white laser is formed into three segments that generate red, green and blue lasers that combine to create a pure white light. Growing the semiconductor on a nanoscale was the key to cracking the problem.
“Lasers are a hundred times faster than LEDs. That’s been demonstrated.”

 

 Underwater Submarine Communications

The Navy is interested in using Li-Fi to improve submarine communications, since radio waves travel poorly under water and current acoustic communications are slow. The underwater VLC in the blue/green spectral range (450 nm-550 nm) is able to achieve data speeds of hundreds of Mbps for short ranges (less than a hundred meter) complementing long range acoustic communication.

 

Metamaterials: Nanopatterned metamaterial boosts LED underwater communications

University of California, San Diego (UCSD) researcher Zhaowei Liu and colleagues have taken the first steps in developing high-modulation-rate blue and green LEDs for underwater optical communications.

They have created a hyperbolic metamaterial (HMM), consisting of layers of Ag and Si patterned with a grating and covered with Rhodamine 6G dye, that boosts the spontaneous-emission rate of a fluorescent light-emitting dye molecule—Rhodamine 6G (R6G)—by a factor of 76, as well as increasing the emission intensity of the dye by a factor of 80.1. Hyperbolic metamaterials are able to achieve plasmonic resonance in which electrons oscillate collectively within a material which, when aligned with fluorescent emission, can amplify the emission.

Gallium nitride (GaN)-based blue- and green-emitting LEDs can achieve extremely high modulation rates, currently they achieve less than 1 GHz. The next step for the researchers will be to pair the nanostructured metamaterial with GaN-based LEDs to develop a better light source for communication purposes. They hope to increase the rate at which information can be sent underwater via optical channels, such as between ships and submarines, submarines and divers, underwater environmental sensors and unmanned underwater vehicles.

But Haas cautiously praised Liu’s results, saying that they could help solve a challenge in the Li-Fi industry if they deliver. Off-the-shelf bulbs are optimized for visible light, not for communications, and so it’s only possible to modulate their intensity comparatively slowly. Liu and colleagues’ blink rate-boosting materials could be a boon. “These devices are perhaps able to provide a step towards the results we would like to achieve,” Haas said

Future Growth

According to the new market research report by MarketsandMarkets, the VLC market is expected to grow from USD 327.8 Million in 2015 to USD 8.50 Billion by 2020, at a CAGR of 91.8% between 2015 and 2020.

The growth of the VLC market is driven by factors such as faster and safer data transfer than other competing technologies, RF spectrum bandwidth crunch, no bandwidth limitation, less energy consumption, and greener, cleaner, and safer technology.

By 2020, the market share of the photodetector segment is expected to grow very rapidly: At present, only one-way communication is possible with the help of VLC, which requires the installation of LED and installation of some applications on phones and tablets, and a cloud server to maintain the storage platform. However, with the advent of two-way communication by the end of 2020, the market share of the photodetector segment, which includes photodiodes and image sensors, is expected to grow very rapidly.

 

The article sources also include:

http://www.techworld.com/big-data/what-is-li-fi-everything-you-need-know-3632764/

http://www.photonics.com/Article.aspx?AID=60893

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