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Li-Fi and Other Visible Light Communications (VLC) Standards

I have been writing about LiFi and other light based communications for a while but it looks like these are finally being standardised and have a potential to be used in commercial devices for communications.

The first thing to mention here is that like there are different brand names for Wi-Fi (like Wi-Fi 5, Wi-Fi 6, etc.), we probably need different names for LiFi. In fact I am not even sure if we write LiFi as one word or Li-Fi. LiFi Tech News describes the technologies as follows:

ITU-T G.9991 standard is the 1st LiFi standard specifying the system architecture, physical (PHY) layer and data link layer (DLL) for high-speed indoor LiFi transceivers, the LiFi access points within LED and infrared lamps.

There are also at least 3 IEEE standards that are being developed to bring LiFi to the mass market. These are the IEEE 802.11bb, IEEE 802.15.7 and IEEE 802.15.13.

IEEE 802.11bb defines one medium access control (MAC) and several physical layer (PHY) specifications for wireless connectivity for fixed, portable, and moving stations (STAs) within a local area. In the near future, it could allow converting any existing WiFi chip solution into a Light Communication solution by adding cheap external circuitry.

IEEE 802.15.7 supports high-data-rate visible light communication up to 96 Mb/s by fast modulation of optical light sources which may be dimmed during their operation. IEEE 802.15.7 provides dimming adaptable mechanisms for flicker-free high-data-rate visible light communication.

IEEE 802.15.13 defines the protocol and compatible network equipment for optical wireless communications and its operation as an optical wireless personal area network (OWPAN) supporting data rates of multiple Gbit/s for wireless speciality applications. The standard defines a medium access control (MAC) layer operating in beacon-enabled or non-beacon-enabled mode and three physical layers (PHYs) enabling low complexity, low power, and high throughput.  It uses light wavelengths from 10,000nm to 190 nm in optically transparent media for optical wireless communications. The standard is capable of delivering data rates up to 2.192 Gb/s at distances in the range of 200 m unrestricted line-of-sight. It is also designed for point-to-point and point-to-multipoint communications and adaptation to varying channel conditions. This standard provides the following new technologies outlined below, which are not included in 802.15.7:

  • Mobility support between LiFi cells and between LiFi and RF
  • Higher data rates through better technologies
  • Up to 10 Gb/s short-range using RGBY LEDs
  • Several 100 Mb/s single-colour in wide beams (a few meters)
  • Discrete multi-tone (DMT, also denoted as DC-OFDM)
  • Closed-loop rate adaptation
  • Multiple-input multiple-output (MIMO) and distributed multi-user MIMO

The chart in the image above (source) shows a comparison between the three IEEE technologies.

The tweet above points to a a recent article in IEEE Spectrum. One thing we may definitely be able to conclude from the article is that LiFi is spelled as Li-Fi. Quoting from the article:

Li-Fi uses variations in the intensity of light to transmit data. The changes are so fast that they are not perceptible to people.

Light waves have frequencies more than 1,000 times greater than radio waves. This means they allow more than 1,000 more channels for communications, which can enable significantly more bandwidth for data. At the same time, Li-Fi does not experience interference from competing radio signals, as do Wi-Fi and 5G devices.

Currently, Li-Fi devices are capable of blazing speeds of 1 Gbps. Research also suggests they can achieve 100 Gbps rates with a multiplexing strategy that simultaneously encodes data on the red, green, and blue channels within a white LED. Multiple lights can make up a single network, letting one move around a space from light to light without interrupting the connection. A clear line of sight is not always needed between the receiver and transmitter—reflections off walls and other surfaces can also carry data.

The new standard for Li-Fi, IEEE 802.11bb, is designed to provide a global framework to deploy light-based devices that are compatible with each other. It was ratified in June.

Critically, the standard was developed for Li-Fi to work alongside Wi-Fi. For instance, with pureLiFi’s Light Antenna ONE—the world’s first device compliant to the new standard—Li-Fi simply appears as if it was another band of Wi-Fi. The module is only 14.5 millimeters wide—smaller than a dime—and designed for integration with existing Wi-Fi chipsets into smartphones, tablets, televisions, virtual reality headsets and more. It can achieve data rates of 1 Gbps or more from a range of 20 centimeters to 3 meters.

For the many devices that do not have Li-Fi antennas built into them, the NEON module from Fraunhofer HHI is a dongle that can attach to laptops and other devices via USB.

In terms of home, office and other indoor applications, pureLiFi has its Li-Fi Cube Gateway, a portable hotspot that can plug-and-play to a network via Ethernet, Powerline or Power over Ethernet. Compliant with the new standard, it can deliver a link of up to 250 Mbps and can sit on a table, rest on an adjustable stand or mount on a ceiling, wall or shelf.

There are outdoors applications for Li-Fi as well—it can work even in sunlight. Fraunhofer HHI has an outdoor Li-Fi point-to-point link that can supply 1 Gbps over 100 meters and 500 Mbps over 200 meters.

Check out the complete article which also contains links to the products it's talking about.

This article from The Verge is also a fantastic place to start on this topic. It points to this presentation, 'IEEE 802 Standards on Light Communication' that details 802.15.13 as well as 802.11bb.

Here is a playlist from Fraunhofer Heinrich Hertz Institute (HHI) that contains all the details about VLC and Li-Fi:

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