Transforming ideas into light bulbs – LiFi

About 4 years ago, Harald Haas, a physicist and professor of mobile communications at the University of Edinburgh, was the first to coin the term Li-Fi, at a TED Talk during TEDGlobal 2011. Since then, millions of bits about this technology roamed the Internet, and many companies already started implementing it.

Who’s doing this already?

The history begins with a company named Velmenni, which has produced a light bulb that works with Li-Fi technology on a small scale. They are not the first to prove the technology works, nor the first to conduct a real-world experiment, but here’s their Jugnu Lighbulb demo.

Philips has developed a VLC (Visible Light Communication) system for shoppers at stores. People have to download an app on their smartphone and then it will interact with the LEDs in the store. The LEDs can pinpoint their location in the store and give them corresponding coupons and information based on which aisle they are on and what they are looking at.Philips-Connected-retail-lighting-system-infographicByteLight has developed a system similar to Philips’ lighting network, making LEDs “talk” to any smartphone and tablet with a camera and/or Bluetooth Smart technology that is “opened to listen”.

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The first VLC smartphone prototype was presented at CES in January 2014, Las Vegas. The phone uses the French SunPartner‘s Wysips CONNECT, a technique that converts light waves into usable energy, making the phone capable of receiving and decoding signals with low battery consumption.

How does Li-Fi work?

Research into VLC has been conducted since 2003, mainly in the UK, US, Germany, Korea and Japan. Experiments have shown that LEDs can be adapted both to accomplish their primary function, which is to emit light, but also to transmit data wirelessly.

VLC exploits a hack of human perception: light-emitting diodes can be switched on and off faster than the eye can detect, causing the light source to appear as “on” in a continuous fashion. Rapid on-off switching enables data transmission using binary code: Switch ON = “1”, Switch OFF = “0”.

A few Tech details

The basic technology that lies ground for Li-Fi is in fact an exploit of a weakness that OFDM (Orthogonal Frequency Division Multiplexing) has. OFDM’s high PAPR (Peak to Average Power Ratio) produces wide fluctuations in the signal. High PAPR results from the nature of the modulation itself, where multiple subcarriers/sinusoids are added together to form the signal to be transmitted. But Haas sorted this out to his advantage, and used it as base for the transmission technique called SIM-OFDM (Subcarrier-Index Modulation OFDM).

More specifically, SIM OFDM relates to adding an additional dimension to the conventional two-dimensional (2-D) amplitude/phase modulation (APM). The key idea of SIM is to employ the subcarrier-index to convey information to the receiver. Further experiments can be made using this method, with an array of LEDs for parallel data transmission, or by applying the mixtures of red, green and blue LED to alter the light’s frequency with each frequency encoding a different data channel.

The standard – IEEE 802.15.7

The standard defining the physical layer and media access control layer is able to deliver enough data rates to transmit audio, video and multimedia services. It takes into account optical transmission mobility, its compatibility with artificial lighting and the interference which may be generated by ambient lighting. The MAC layer permits using the link with protocol stacks such as TCP/IP.

Is there a catch?

The biggest downside Li-Fi has in comparison with classical WiFi is that once you are no longer in the range of the light source, you are no longer connected.

However, there is also a big win to having Internet distributed by light, and that is the fact that no one can steal your data without actually being in your house, so forget about passwords!

What’s next?

Well, Haas has furthered his research and came up with a new concept for Li-Fi, suitable for places lacking infrastructure – Solar LiFi, using off-the-shelf LEDs and solar cells. He presented the experiment in his latest TED Talk.

 

This is, in my opinion, the next step in IoT

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