What is Li-Fi and how does it work? Li-Fi is a new method of wireless communication, which may replace or augment traditional wireless technologies (e.g. Wi-Fi, 4G). Interest in Li-Fi took off after a 2011 TED talk titled “Wireless data from every light bulb” and excitement in the technology has been growing ever since . The key difference between Li-Fi and Wi-Fi is the method used to transmit signals. In Li-Fi, the signal is sent using visible or infrared light, while in Wi-Fi the signal is sent using invisible radio waves.
To understand the advantages and disadvantages of Li-Fi, it is instructive to look at a basic Li-Fi set up. The schematic to the right shows how a laptop could connect to the internet via Li-Fi. The ceiling hub is analogous to a Wi-Fi router and is connected to the internet. Connected to the ceiling hub are a LED (to send signals) and a detector (to receive signals). The desktop hub in the figure is like a Wi-Fi modem integrated into a laptop and receives the Li-Fi signal and turns it into an internet connection for the laptop. The desktop hub also has its own LED to send signals.
In this system, signals from the ceiling hub are sent downward by flickering the LED on/off. LEDs can be turned on/off extremely fast, which enables high data transfer speeds. Furthermore, because the LED flickers so quickly, people in the room would just see normal steady illumination from the ceiling LEDs. The detector in the desktop hub detects when the light turns on/off and thus downloads information. In a way, the flickering light is like extremely high speed Morse Code. For the laptop to upload data to the internet, the LED in the desktop hub sends signals up to the detector on the ceiling. The LED in the desktop hub is likely to transmit data with infrared light (not visible to the human eye) so that the laptop user is not annoyed by an upward shining light. Overall the basic components and power requirements are similar to those needed for Wi-Fi .
What are the main pros and cons of Li-Fi? The potential advantages of Li-Fi technology over Wi-Fi are higher speed, fewer interference issues, better security, safer use in sensitive environments, more frequencies for communication, and better location service. These advantages all stem from the use of visible light instead of radio waves to transmit the signal. Theoretically, Li-Fi can achieve speeds >100 Gbps, while commercially available Wi-Fi routers struggle to achieve speeds above 1 Gbps and 4G and Bluetooth connections max out at much less than 1 Gbps . Thus, the higher transfer speeds could make Li-Fi advantageous for applications that require very high bandwidth wireless connections. As most people have experienced, Wi-Fi and 4G also suffer reliability issues in high traffic and densely populated areas. A Li-Fi network will not have such an issue since the data density of a Li-Fi signal is ~1,000x higher than that of Wi-Fi, and the bandwidth of visible light is ~10,000x larger than that of radio waves . As far as security is concerned, a Li-Fi signal is hard to intercept because you must be able to see the light in order to receive the signal. Thus, a signal inside a closed room is contained and cannot be snooped on by people in the next room. Another advantage of Li-Fi is safety in settings with sensitive equipment that can be affected by radio waves. The last advantage of Li-Fi is precise location tracking. Since Li-Fi signals do not travel through walls, ceilings, or floors, determining the location of a user on a Li-Fi network is relatively simple (they must be near the LED).
The disadvantages of Li-Fi are its requirement for light of sight of the signal, its low range, and the lack of market products and infrastructure. First and foremost, a signal can only be transmitted if the detector is able to visibly see the light signal. This means a Li-Fi enabled laptop would lose its connection if a piece of paper were placed over the Li-Fi detector, and a Li-Fi enabled phone would not receive a signal when in the user’ pocket. Unlike Wi-Fi where the signal propagates through the walls of a space, it is much more difficult to maintain a Li-Fi connection as someone moves throughout a building. Another issue is the limited range of Li-Fi. Li-Fi range is affected by the background level of light, so it is more difficult to send a signal outdoors because the sun can overwhelm the Li-Fi signal. Thus, in brightly lit buildings or outside, many LEDs would be needed to cover a space in Li-Fi signals. Lastly, there are few products available today to enable Li-Fi. The currently available Li-Fi system from pureLiFi (LiFi-X) achieves a speed of around 0.05 Gbps and a significant amount of further development is needed to increase speed and decrease cost . Lastly, no laptops or cellphones have integrated equipment to utilize Li-Fi, so devices would need dongles or peripherals to send/receive Li-Fi signals.
What are the potential applications? The applications for Li-Fi must take advantage of the technology’s distinct advantages noted above. One cannot simply use Li-Fi in place of Wi-Fi for any given application and expect a boost in performance. Additionally, it may be the case that Li-Fi should not displace Wi-Fi at all and is better suited to supplement Wi-Fi for high bandwidth communication in areas with high traffic or in areas where Wi-Fi does not work well due to interference. That said, we believe Li-Fi may find applications in the following areas:
Indoor location tracking – If consumers have Li-Fi enabled devices and Li-Fi LEDs are installed throughout a building, one could accurately track where consumers are. The accuracy of the location tracking would be determined by the density of LEDs installed in the buildings (more LEDs, better accuracy). Additionally, Li-Fi could enable walking guides through cities or museums and real-time location based advertising to consumers.
High density wireless internet – Li-Fi could be used in sports stadiums, large conference rooms, or rooms/lobbies with large crowds. Since the data density is high, the Li-Fi network would be able to supply bandwidth to many users simultaneously.
Automotive applications – LED headlights and tail lights could provide a means of communication between vehicles and between vehicles and infrastructure. Li-Fi would provide a high speed wireless communication method in this scenario and could enables things like real-time map updates or routing information.
Areas where Wi-Fi struggles – Wi-Fi technology struggles to perform well in some structures because of interference issues. Examples include some parking garages, buildings with complex internal structures, and mine staffs. In these cases, Li-Fi could fill the gap and provide wireless communication.
Smart lighting and the Internet of Things – LED street lights or other lights inside or outside of buildings could provide wireless internet connectivity to users near the light sources. Using this method, street lights could provide wireless internet and sensors throughout cities could stream data to the cloud. The large bandwidth of visible light would allow many devices to communicate wireless without the fear of “spectrum crunch.”
Replacement for RFID/NFC technology – These technologies utilize radio waves to send and receive signals and are used to power things like Apple Pay and remote building access. A similar system based on Li-Fi would allow faster communication and could possibly be more secure from eavesdroppers.
RF sensitive environments – Environments such as hospitals, refineries, and mines are sometimes unable to use traditional radio frequencies for communication because of potential interference issues with equipment or because of fire concerns. Li-Fi could be used as a Wi-Fi replacement.
Who is working on Li-Fi? There are several companies working on Li-Fi technologies, but there are few, in any, commercial products available for purchase. pureLiFi is one of the better known Li-Fi focused startups having raised >$20M in funding. It has a prototype product and aims to enable ubiquitous, high-speed, secure data networks wherever there is LED illumination. Other startups include OLEDcomm (France), VLN Comm (USA), and Velmenni (Estonia).
Several large corporations have also shown interest in Li-Fi, though it is less clear what their intentions are and where they are in the technology development cycle. In 2015, Acuity Brands, a large lighting company, acquired ByteLight, a startup that was developing an indoor location service technology based partially on Li-Fi. Phillips is also interested in Li-Fi for smart lighting and for indoor location tracking and recently acquired Luciom, a French Li-Fi startup. Furthermore, Apple and Samsung have both been rumored to be exploring Li-Fi for future applications, but their intentions are unknown.
 http://www.techworld.com/big-data/what-is-li-fi-everything-you-need-know-3632764/, https://www.verizonwireless.com/archive/mobile-living/network-and-plans/4g-lte-speeds-compared-to-home-network/, https://en.wikipedia.org/wiki/Bluetooth
 http://theinstitute.ieee.org/members/profiles/learn-how-lifi-works-from-its-inventor-harald-haas, http://spie.org/newsroom/4773-high--speed-wireless-networking-using-visible-light