High-Tech Li-Fi Based on Age-Old Technologies

High-Tech Li-Fi Based on Age-Old Technologies

This piece was originally published in the September 2018 issue of electroindustry.

Thomas D. Little, PhD, Professor, Boston University Department of Electrical and Computer Engineering

Dr. Little is the associate director at the National Science Foundation Engineering Research Center for Light Enabled Systems & Applications (LESA)

Visible light communication (VLC) sounds like a newfangled notion, but it’s not.

The ancient Greeks shined light across the sky to communicate quick and urgent messages; in Boston, Paul Revere famously signaled “one if by land, two if by sea” using lantern-based semaphores; and Alexander Graham Bell developed his photophone to transmit speech on a beam of light in 1880.

Today, VLC refers to using the visible part of the optical spectrum to communicate data. With the invention of energy-efficient light-emitting diodes (LEDs) and laser diodes (LDs), it is possible to encode data into the visible spectrum to achieve very high rates, comparable to Wi‑Fi. Where Wi-Fi uses radio waves for transmission, Li-Fi (short for light fidelity) uses light. Li-Fi is often used to describe high-speed VLC in scenarios where Wi-Fi might also be used.

Emerging Standards for VLC include such camera-based techniques as CamCom (IEEE 802.15.7m), a proposed vehicular assistant technology that uses image sensor communication in intelligent transportation systems, and Li-Fi (IEEE 802.11lc and IEEE 803.15.13), which promote interoperability among solid state light sources. These Standards emerge from different technology standpoints, targeting a range of use cases.

A critical factor for these new technologies is the ability to exploit the visible spectrum. This has advantages and disadvantages. A big plus is the ability to piggyback on lighting functions so that wherever there is lighting, there can be data communications. This use is opportunistic, exploiting the “free” spectrum that is not otherwise used for communications. Light is also highly directional, and this property can be exploited to improve data security and to realize many private data links in close proximity.

On the negative side, VLC must conform to human factors, including freedom from flicker and glare, and must meet color rendering index (CRI) and light distribution goals.

VLC technologies have the potential to provide access to unused spectrum that will ensure growth in wireless capacity beyond the crowded radio frequency bands. VLC also promises to do this using deployed lighting, offering the potential to both use existing infrastructure and leverage the other features offered when lighting is computer controlled.

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