Li-Fi

It’s impossible to avoid Wi-Fi in today’s world. It’s everywhere; your neighbors have it, it’s free in coffee shops, and essential for smartphones. We all know Wi-Fi, but what is Li-Fi? Li-Fi, like Wi-Fi, enables electronic devices like computers, laptops and smartphones to wirelessly connect to the Internet. Even though Wi-Fi was also originally intended for such devices, it is widely used today to connect all sorts of things: printers, televisions, speakers, headphones, and even running shoes! In simple terms, Li-Fi is equivalent to Wi-Fi, but using light waves instead of radio signals. Li-Fi uses the light waves from LED light bulbs – that are rapidly replacing incandescent light bulbs for their energy saving and safety - to transmit data so it provides illumination and wireless data communications. Imagine a modern LED light bulb – fitted with Li-Fi technology – in your living room, or office, or in a lamp on your desk, or by your bedside. Anywhere that is illuminated by the Li-Fi enabled LED, can also communicate via Li-Fi.

What Is LiFi?

The term LiFi was coined by Professor Harald Haas, and is recognized by the IEEE standardization committee for Optical Wireless Communications. LiFi is high-speed, bidirectional, networked and mobile wireless communications using light (as opposed to traditional radio frequencies). With LiFi technology, data travels in the visible light spectrum through LEDs.  This makes it possible to provide wireless internet access at speeds of over 100 Gbps, although this is still in the Lab. Although Li-Fi can be used to off-load data from existing Wi-Fi networks, implementations may be used to provide capacity for the greater downlink demand such that existing wireless or wired network infrastructure may be used in a complementary fashion.

LiFi is the use of the visible light portion of the electromagnetic spectrum to transmit information at very high speeds. This is in contrast to established forms of wireless communication such as Wi-Fi which use traditional radio frequency (RF) signals to transmit data.

With LiFi, data is transmitted by modulating the intensity of the light, which is then received by a photo-sensitive detector, and the light signal is demodulated into electronic form. This modulation is performed in such a way that it is not perceptible to the human eye.

LiFi is a category of Optical Wireless Communications (OWC). OWC includes infra-red and ultra-violet communications as well as visible light. However, LiFi is unique in that the same visible light energy used for illumination may also be used for communication.

How Does Li-Fi Work?

When a constant current is applied to an LED light bulb a constant stream of photons are emitted from the bulb which is observed as visible light. If the current is varied slowly the output intensity of the light dims up and down. Because LED bulbs are semi-conductor devices, the current, and hence the optical output, can be modulated at extremely high speeds which can be detected by a photo-detector device and converted back to electrical current. The intensity modulation is imperceptible to the human eye, and thus communication is just as seamless as RF. Using this technique, high speed information can be transmitted from an LED light bulb.

Radio frequency communication requires radio circuits, antennas and complex receivers, whereas Li-Fi is much simpler and uses direct modulation methods similar to those used in low-cost infra-red communications devices such as remote control units. Infra-red communication is limited in power due to eye safety requirements, whereas LED light bulbs have high intensities and can achieve very large data rates.

Ranjan Tyagi

Batch 2015-17

Symbiosis Institute of Telecom Management