A new way to transmit data is coming that could radically change the way that devices talk to each other: LiFi. Short for Light Fidelity, LiFi uses visible light to send data, creating the link between router and device with invisible pulses of light. This type of Visible Light Communication (VLC) uses something that is present in pretty much every room: an LED lightbulb.
What is LiFi?
Li-Fi sounds like the an engineer’s fevered dream: it is fast, cheap, secure and simple to implement. Speeds of up to 10Gbps have been demonstrated in the lab, and products are now available that offer 10Mbps speed. It is cheap because it can use a modified LED lightbulb. It is secure because it only works where the light is visible: step out of the room and the signal is lost. It is simple to implement because it uses an existing technology: LEDs.
The basis of the technology is in turning the LED light on and off very fast. By switching an LED on and off millions of times a second, you can create a data signal that can be detected by a sensor, but which is invisible to the human eye. At the other end, another LED detects these pulses, and can send light pulses back in response, creating a bi-directional link. If you combine this with wired Ethernet or a WiFi network, you have an awesome combination: an Internet connection that uses visible light for the last link.
One way to think of this is like an Infra-Red remote control, but on steroids. Your IR remote works by turning an IR LED on and off at a frequency of about 38KHz, encoding data at a speed of up to 120bps. A sensor and a microcontroller in your TV detects this light, and converts it into commands. Some computers and PDAs in the 1990s used a faster standard called IrDA, which could send data at kilobit speeds. IrDA never really caught on, though, although the group behind it is working on new versions that could up the speed to 10Gbps.
Li-Fi uses a similar idea to IrDA, but with visible light instead of IR. This has the advantage of being a wider chunk of the electromagnetic spectrum, and with some clever encoding, the red, green and blue elements of modern white LEDs can be used to increase the amount of data that can be sent, a technique called Color Shift Keying (CSK). Because the data is being sent by LED light sources, it can also be focused. Literally: you can use lenses to direct the signal.
The proponents of this technology are planning to build networks using small LED devices on the ceiling of a room which they call attocells. Because they use visible light, these attocells can be shaped to transmit and receive over a very small (and focussed) angle, so they won’t interfere with each other like WiFi devices can. In a recent paper, the proponents of this technology claim that, in a typical 400 square meter office, this could deliver between 12 and 48Gbps to devices: significantly more than a WiFi or other wireless network that has to deal with interference from other similar devices.
Another interesting new development is combining a Li-Fi signal with a solar cell. With a bit of clever engineering, the solar cell can both power a small device and receive the Li-Fi signal. So, a device could receive both power and data from the same source, which could be very useful for Internet of Things devices or small sensors.
Are There Any Standards for Li-Fi?
At the moment, there are no real standards for Li-Fi. The systems that are currently available are partly based on the IEEE 802.15.7 standard that defines the physical layers of the network, but this is rather out of date. Standards are coming, though: the Li-Fi consortium is the main group working to create a WiFi-like standard that will provide the same sort of interoperability that WiFi devices have. There is no timeline for this at the moment, though.
How Can I Try Li-Fi?
There are two ways at the moment: buy one of the first devices, or make your own. PureLiFi was the first company to sell a LiFi device: the Li1st. Since then, the company has also added the LiFlame, a first version of their attocell concept. Using a device on the ceiling and a USB transceiver, it can send and receive data at up to 10Gbps.
The other alternative is to make your own. Disney Research has published a paper that shows how they built a Li-Fi like device into an existing light socket using an Atheros SoC board running Linux. Unfortunately, they have not published any schematics or code for this.
Hackaday reader [jpiat] has, though: his project uses an Arduino to control of an RGB LED light to send data using a modified 1-Watt LED light. His system only works in one direction, but it is very simple: the Arduino uses simple encoding on the data, and three data lines to control the LED. It is robust enough to send at a decent speed, though: he claims that it can manage an impressive 1kbps speed using a 1-Watt LED light to a distance of 3 meters. That’s an impressive glimpse of our Li-Fi future.