Li-Fi claims to be 100 times faster than standard Wi-Fi. But what exactly is it. Li-Fi is a bidirectional, high-speed and fully networked wireless communication technology similar to Wi-Fi. The term was coined by Scientist Harald Haas and is a form of optical wireless communications (OWC) and uses the visible spectrum as well as ultraviolet and infrared radiation. Li-Fi could be a complement to RF communication (Wi-Fi or cellular networks), or even a replacement in contexts of data broadcasting. It is currently being developed by many organisations all over the world. 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.
Who is Harald Haas?
Scientist Professor Harald Haas FRSE is German, Professor of Mobile Communications at the University of Edinburgh and is the person who coined the term Li-Fi. Haas was elected a Fellow of the Royal Society of Edinburgh in 2017. Someday the last leg of our communication networks might not depend on a modulated radio signal but on a modulated light signal from an LED bulb in a desk lamp or ceiling fixture. IEEE Senior Member Harald Haas has developed a visible light communication system he calls light fidelity, or Li-Fi, which relies on nanometer waves in the infrared and visible light part of the electromagnetic spectrum to transmit data generated by an LED bulb fitted with a microchip. Haas demonstrated in 2011 how light fidelity technology works in a TED Global talk. Viewers dubbed him the “father of Li-Fi.”
A professor of mobile communications at the University of Edinburgh, Haas established the LiFi Research and Development Centre at the school to conduct R&D on the technology. In 2012 he helped found pureLiFi, also in Edinburgh, to commercialize the technology. The company recently unveiled several products. Also Haas received the International Solid State Lighting Alliance’s outstanding achievement award for his “contribution to diversifying the applications of solid-state lighting technology.”
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 causing electromagnetic 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, Ultraviolet and Infrared. 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 224 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.
How it works
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. The system has two basic parts: an LED bulb that transmits modulated signals and a separate photo detector—a photodiode—connected to a computer or other Internet-enabled device that displays the decoded signals. Haas developed a transmission technique, called spatial modulation–orthogonal, frequency division multiplexing or SM-OFDM that enables a light source to transmit data rapidly and in an energy-efficient manner.
The LED bulb is a semiconductor light source, and the current supplied to it can be modulated—by a microchip that Haas’s team developed, which is placed in the bulb fixture, or luminaire. Light from the bulb can be intensity-modulated at high speed. The modulation is invisible to the human eye. Data is fed into the LED bulb, which sends data embedded in its light at rapid speeds to the photodiode, which is some distance away. Currently, that device is housed in a dongle pureLiFi recently introduced that plugs into a standard USB port.
The communication link behaves as seamlessly as do the radio signals of a Wi-Fi system, according to Haas. “Data rates in ideal conditions have been as high as 100 gigabits per second (Gb/s), which means approximately 12 full-length high-definition movies could be downloaded in a second,” he says.
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.
Step up from WI-FI
Li-Fi doesn’t interfere with other RF devices in the area. And increased data density—approximately 1,000 times the data density of Wi-Fi—reduces the need for users to share the wireless bandwidth with others. For security purposes, the visible light can be contained in a defined area: Just close the doors, pull down the window shades, and shut the drapes and you lock in your data. Unlike RF, the light won’t travel through walls. What’s more, the LED bulbs can be dimmed to such a point that they appear off, even while they’re still transmitting data, Haas says.
The light signals of an LED bulb do have a relatively short range compared with RF, he points out. So the farther away from the light source, the slower the speed. “You don’t have to be under the LED bulb to access Li-Fi, because the system can use light reflections from walls and other surfaces,” Haas says. “So, clearly, it is a non-line-of-sight technology.” Practical data speeds in his Li-Fi products have averaged 25 Mb. Unlike, RF, Li-Fi is unaffected by interference from cordless phones, microwave ovens, machinery, or similar sources.
Li-Fi vs Wi-Fi
While some may think that Li-Fi with its 224 gigabits per second leaves 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 light bulb is on at all times to provide connectivity, meaning that the lights will need to be on during the day.
Additionally, where there is a lack of light bulbs, 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, 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 smart watches; smart phones 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.
Who is investing in Li-Fi?
Li-Fi pioneer’s pureLiFi joined forces with French lighting company Lucibel to launch Li-Fi enabled products. PureLiFi introduced its first LiFi-X dongle February 2017. About the size and width of a business card, LiFi-X plugs into a computer’s USB port. An optical device that accepts signals from the LED bulb, the dongle holds a receiver that converts the light-intensity variations of the LED into an electric signal, which is then converted back into a data stream that is transferred to a computer. The dongle also contains a digital data modulator that works with an infrared LED to provide full duplex bidirectional wireless access at 43-Mb download and upload speeds.
Those are the highest practical data rates of the Li-Fi systems, Haas says. He notes that a single Li-Fi luminaire can communicate simultaneously with multiple dongles, for what’s referred to as multiuser access. Moreover, if a mobile device moves into the illumination area of another Li-Fi-enabled luminaire, the system invokes a seamless handover, so the device is always served by the best-placed luminaire.
Through a partnership with the French lighting manufacturer Lucibel, pureLiFi has built a Li-Fi system for office buildings. Included are luminaires that hold the LED bulbs as well as the modulating and demodulating circuits and digital signal processors that run the communication protocols as firmware. LED bulbs installed in the ceilings can be networked into the company’s IT architecture, so people using a computer or mobile device outfitted with the LiFi-X dongle can access data from office LEDs anywhere in the building.
The first Li-Fi-enabled system was installed in June 2016 throughout the 3,500 square meters of the Paris headquarters of Sogeprom, a real estate developer. A number of pilot projects are under way in Singapore, according to Haas, spearheaded by the country’s Info-communications Development Media Authority. The cost of each lighting system is now negotiated individually, says Haas, who expects costs to go down with volume.
Connected cars, the digital aircraft cabin, virtual and augmented reality applications, and the Internet of Things are other possible applications for Li-Fi, Haas says. For example, the technology could provide a bidirectional communication link between cars through their LED headlights and added sensors. And Li-Fi-enabled LED streetlights and traffic lights could communicate with driverless cars to keep them from crashing into each other.
“Li-Fi could also provide a big, fat data pipe for virtual-reality applications,” Haas says. “And it could be ideal for the Internet of Things, linking low-power sensors in industrial equipment or home appliances. “We are living in what author and economist Jeremy Rifkin called the ‘Third Industrial Revolution’ in his best-selling book of the same name. That revolution is all about data, and economies are built around data. Making sense out of data means you not only have to create, analyze, and process data, you also have to transmit it. All intelligent biological systems have a nervous system, and Li-Fi may provide the nervous system of our future smart world that will be full of artificial intelligence!
Scientist Professor Harald Haas
Professor Harald Haas, coined the term “Li-Fi” at his 2011 TED Global Talk where he introduced the idea of “Wireless data from every light”. He is a Chair Professor 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. Oledcomm, french company founded by Pr Suat Topsu from Paris-Saclay University.
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 GB/s across a light spectrum emitted by LED lamps.
Recent integrated CMOS optical receivers for Li-Fi systems are implemented with avalanche photodiodes (APDs) which has a low sensitivity. 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. Also this operation could be performed as quantum-limited sensitivity that makes receivers detect weak signals from far distance.
Like Wi-Fi, Li-Fi is wireless and uses similar 802.11 protocols; but it uses Ultraviolet, Infrared and visible light communication (instead of radio frequency waves), which has much bigger bandwidth. One part of VLC is modelled 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 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.
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. The 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.