Electronics for You, April 2012
Li-Fi: A New Paradigm in Wireless
Lighting reaches nearly everywhere, so communications can ride along for nearly free. Think of a TV remote in every LED light bulb and you’ll soon realise the possibilities of communications using visible light—also dubbed as Li-Fi.
Dr Frank Deicke, Walter Kraus, Dr Josef Shwartz, Rudi Wiedemann
Most of us are familiar with Wi-Fi (Wireless Fidelity), which uses 2.4-5GHz RF to deliver
wireless Internet access around our homes, schools, offices and in public places. We have become quite dependent upon this nearly ubiquitous service. But like most technologies, it has its limitations.
While Wi-Fi can cover an entire house, its bandwidth is typically limited to 50-100 megabits per second (Mbps) today using the IEEE802.11n standard. This is a good match to the speed of most current Internet services, but insufficient for moving large data files like HDTV movies, music libraries and video games.
The more we become dependent upon ‘the cloud’ or our own ‘media servers’ to store all of our files, including movies, music, pictures and games, the more we will want bandwidth and speed. Therefore RF-based technologies such as today’s Wi-Fi are not the optimal way. In addition, Wi-Fi may not be the most efficient way to provide new desired capabilities such as precision indoor positioning and gesture recognition.
Optical wireless technologies, sometimes called visible light communication (VLC), and more recently referred to as Li-Fi (Light Fidelity), on the other hand, offer an entirely new paradigm in wireless technologies in terms of communication speed, flexibility and usability.
Visible light communications
Many people’s first exposure to optical wireless technology was VLC. This emerging technology offers optical wireless communications by using visible light. Today, it is seen as an alternative to different RF-based communication services in wireless personal-area networks. An additional opportunity is arising by using current state-of-the-art LED lighting solutions for illumination and communication at the same time and with the same module. This can be done due to the ability to modulate LEDs at speeds far faster than the human eye can detect while still providing artificial lighting.
Thus while LEDs will be used for illumination, their secondary duty could be to ‘piggyback’ data communication onto lighting systems. This will be particularly relevant in indoor ‘smart’ lighting systems, where the light is always ‘on.’
Other examples for outdoor use include intelligent traffic systems to exchange data between vehicles, and between vehicles and road infrastructure like traffic lights and control units. Alternatively, the LEDs’ primary purpose could be to transmit information while the secondary purpose of illumination would be to alert the user to where the data is being transmitted from.
In contrast to infrared, the so-called “what you see is what you send” feature can be used to improve the usability of transmitting data at shorter point-to-point distances between different portable or fixed devices. There, illumination can be used for beamguiding, discovery or generating an alarm for misalignment.
The premise behind VLC is that because lighting is nearly everywhere, communications can ride along for nearly free. Think of a TV remote in every LED light bulb and you’ll soon realise the possibilities of this technology.
One of the biggest attractions of VLC is the energy saving of LED technology. Nineteen per cent of the worldwide electricity is used for lighting. Thirty billion light bulbs are in use worldwide. Assuming that all the light bulbs are exchanged with LEDs, one billion barrels of oil could be saved every year, which again translates into energy production of 250 nuclear power plants.
Driven by the progress of LED technology, visible light communication is gaining attention in research and development. The VLC Consortium (VLCC) in Japan was one of the first to introduce this technology.
After establishing a VLC interest group within the IEEE 802.15 wireless personal-area networks working group, the IEEE 802.15.7 task group was established by the industry, research institutes and universities in 2008. The final standard was approved in 2011. It specifies VLC comprising mobile-to-mobile (M2M), fixed-to-mobile (F2M) and infrastructure-to-mobile (I2M) communications. There, the focus is on low-speed, medium-range communications for intelligent traffic systems and on high-speed, shortrange M2M and F2M communications to exchange, for example, multimedia data. Data rates are supported from some 100 kbps up to 100 Mbps using different modulation schemes.
Other standardisation groups are working on standardised optical wireless communication (OWC) solutions using visible and infrared light. The most important groups are IrDA with its new 10 Giga-IR working group, ISO and ICSA.
Li-Fi—the superset of VLC & Co.
VLC represents only a fraction of what appears to be a much larger movement towards optical wireless technologies in general. This larger world has been dubbed ‘Li-Fi’ (Light Fidelity) by people such as Dr Harald Haas of Edinburgh University and organisations such as the Li-Fi Consortium.
In that connection, Li-Fi comprises several optical wireless technologies such as optical wireless communication, navigation and gesture recognition applied for natural user interfaces (Fig. 1). Thus it provides a completely new set of optical technologies and techniques to offer users add-on as well as complementary functionalities compared to well-known and established RF services. This could reach from a new user experience regarding communication speeds in the gigabitclass to bridge the well-known spectrum crunch, over to precise indoor positioning or controlling video games, machines or robots with entirely new natural user interfaces. Finally, these and many more could be merged to a full-featured Li-Fi cloud providing wireless services for other future applications
What Li-Fi stands for
Li-Fi comprises a wide range of frequencies and wavelengths, from the infrared through visible and down to the ultraviolet spectrum. It includes sub-gigabit and gigabit-class communication speeds for short, medium and long ranges, and unidirectional and bidirectional data transfer using line-of-sight or diffuse links, reflections and much more. It is not limited to LED or laser technologies or to a particular receiving technique. Li-Fi is a framework for all of these providing new capabilities to current and future services, applications and end users.
Within a local Li-Fi cloud several databased services are supported through a heterogeneous communication system. In an initial approach, the Li-Fi Consortium defined different types of technologies to provide secure, reliable and ultra-high-speed wireless communication interfaces. These technologies included giga-speed technologies, optical mobility technologies, and navigation, precision location and gesture recognition technologies.
For giga-speed technologies, the Li-Fi Consortium defined GigaDock, GigaBeam, GigaShower, GigaSpot and GigaMIMO models (Fig. 2) to address different user scenarios for wireless indoor and indoor-like data transfers. While GigaDock is a
wireless docking solution including wireless charging for smartphones, tablets or notebooks, with speeds up to 10 Gbps, the GigaBeam 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.
GigaShower, GigaSpot and Giga- MIMO are the other models for in-house communication. There a transmitter or receiver is mounted into the ceiling connected to, for example, 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. GigaShower provides unidirectional data services via several channels to multiple users with gigabit-class communication speed over several metres. This is like watching TV channels or listening to different radio stations where no uplink channel is needed. In case GigaShower is used to sell books, music or movies, the connected media server can be accessed via Wi-Fi to process payment via a mobile device. GigaSpot and GigaMIMO are optical wireless single- and multi-channel HotSpot solutions offering bidirectional
gigabit-class communication in a room, hall or shopping mall for example.
How Li-Fi works
Imagine yourself walking into a mall where GPS signals are unavailable but the mall is equipped with ceiling bulbs that create their own ‘constellation’ of navigation beacons. As the camera of your cellphone automatically receives these signals, it switches your navigation software to use this information to guide you to the ATM machine you’re
You conclude your ATM transaction and notice the GigaSpot sign for instant digital movie downloads. You pick out that new Tom Cruise movie using your phone’s payment facility, and then download within a few seconds the high-definition movie into the GigaLink flash drive plugged into the USB port of your smartphone.
As you walk away, your phone notifies you that the leather jacket Tom featured in the movie is on sale nearby. You walk over towards the show window and your image comes up on the screen, wearing that coveted jacket. You turn and pose while the image matches your orientation and body gestures for a ‘digital fitting.’ When you walk into the store, the clerk hands you the actual jacket in exactly your size.
On the verge of a breakthrough
First applications of Li-Fi have been put to use already, for example, in hospitals where RF signals are a threat due to interference problems with medical equipment such as blood pumps and other life supporting instruments. Axiomtek Europe presented such a product at the Embedded World exhibition in Nu?rnberg, Germany. The prototype of a mobile phone with an incorporated VLC system was presented by Casio at the Consumer Electronics Show in Las Vegas in January this year. In the coming years, we will see more Li-Fi products entering the market, both in the industrial as well as consumer markets.
The authors are co-founders of the Li-Fi Consortium — a non-profit organisation focusing on optical wireless technologies and fostering the Li-Fi cloud in general.