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Light up the Fastest Era Ever100 times faster than Wi-Fi, Li-Fi generation begins
Shin Eun-soo 기자  |  sesoo0315@yonsei.ac.kr
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승인 2014.04.08  21:00:02
트위터 페이스북 구글 카카오스토리

STANDING UNDER the light, sending a music video of Girls’ Generation to your friend is no longer time consuming, just as if you were sending a text message. At the end of October, 2013, the “Massively-parallel visible light communication project team” from Oxford University and Cambridge University successfully demonstrated the new wireless communications technology called ‘Li-Fi’. Using visible light from LED, the team has succeeded in exchanging data at the speed of 10Gb/s. Since 1Gb is equal to 1000Mb, it is 100 times faster than the most widely used wireless technology, Wi-Fi with the speed of 100Mb/s, and 66 times faster than the fastest wireless technology in use, LTE-A with 150Mb/s.

   The word ‘Li-Fi’ was first created by professor Herald Hass from Edinburgh University. “Li” from Li-Fi stands for “light”, and “Fi”, just like Wi-Fi, means fidelity which measures the consistency of the telecommunication. As we can see from the origin of its name, Li-Fi is a light-powered Wi-Fi. This light, however, does not refer to any kind of light such as sunlight. It specifically refers to the LED(Light Emitting Diode) lighting.

Compared to other types of lights, LED has many superior characteristics. For example, LED greatly excels incandescent light, which was the most widely used light source before LED, because of its lower energy consumption, flexibility in usage,  longer lifetime, and smaller size. Compared to LED, the fluorescent light wastes most of their electric energy in the form of heat. As such, the current trend is to replace these with LED which has higher efficiency in energy consumption. Currently, LED is used in various ways including: aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, and camera flashes. LED is everywhere, and just because of this ubiquity, LED was nominated as the potential energy source for faster telecommunication. The point that researchers are making is that if the current trend is to change other lights to expensive LED due to its efficiency, why not make use of it?

Since there are many other sources for telecommunication, some people might wonder, “How did light come to be used in telecommunication?” Using light to telecommunicate might sound strange, but there are many examples of light being used for information exchange throughout history. The easiest example would be signals we see every day when we cross the street. Back in the Chosun dynasty, people lit up signal fires called *bonghwa* to alert soldiers of an impending enemy invasion. Indians reflected the sun light with mirror to communicate with each other from the long distance. Some modern examples are the lighthouses in the sea which helps ships find their way, and the navy sends strategic signal to notify each other. Likewise, LED is also playing the role as a signal in the form of Li-Fi. During data transfer, the LED blinks 200 times per second, widening the range of paths data can go through, letting large amounts of data flow very fast. Human eye cannot sense blinking more than 100 times per second, but the computer can sense it, and further interpret it. Computer language is consisted of two simple numbers, 0 and 1. With the LED method, light on means 1, and no light means 0.

   Being able to blink fast and signal is one advantage Li-Fi has, but the biggest advantage is that it can deliver big data quickly, and the secret to Li-Fi’s biggest advantage is called orthogonal frequency division multiplexing (OFDM). OFDM divides one frequency into various bandwidths, dividing the information when sending and putting them together when receiving. Suppose a frequency is a group of travellers trying to enter a castle. Using OFDM, these travelers can be separated into smaller groups and go through different gates into the castle, making the traffic much lighter. Although LTE-A uses the same technology, Li-Fi is 66 times faster than LTE-A. This is because the frequency bandwidth, the width of the road the frequency travel in, is different between Li-Fi and LTE-A. While mobile communication and wireless lan use a frequency range of around 300MHz (megahertz) to 30GHz (gigahertz), visible ray’s frequency range from 380THz to 750THz, more than ten thousand times wider than the whole wireless frequency width. Also, too many people use the same range of frequency together when using the wireless lan, which causes the frequency to interfere with each other as if too many cars were in the road causing a traffic jam. The consequence is the low communication quality. However, with wider frequency ranges through Li-Fi, it is much more convenient for frequency to reach its destination, just like the principle where the same number of people having less chance of bumping into each other when they are in a bigger room.

   Of course there are disadvantages in Li-Fi since its source is visible light. The most crucial disadvantage is that communication is only possible when there is light. Visible light cannot pass through solid objects, and simply covering the receiver, such as a cell phone, with a paper can interrupt communication. Thus, this technology cannot be used over long distances or in a light deprived room. Even when there is light other than LED, Li-Fi gets interrupted. As a result, it is difficult to use Li-Fi outdoors, since visible light from the sun can interfere with the LED lighting that the user is trying to reach.

 However, in places like complex underground markets or large department stores, such disadvantages can actually be advantageous. It is easy to get lost in a grand mall, and due to the high density of people in the mall, it is not easy to gain Wi-Fi access to help with navigation. But when Li-Fi is in use, you can quickly download information or find your way around wherever there is light. Just as mentioned above, Li-Fi has a wider frequency range making its connection more consistent than Wi-Fi, and wherever LED light is on, you can utilize this advantage.

   Last year, when massively-parallel visible light communication project team first announced their success people rushed to invest in Li-Fi. It was no surprise that so many people eagerly invested in it, considering the advantages Li-Fi had to offer and the new future it can bring about. But, Moon Kyeong-joon(analyst, IM Investment) warns not to be too hasty. “We have to keep in mind that it takes some time for the Li-Fi to be used in everyday lives, and there are many technological aspects that need more research.” Just as he said, the time when we would be using Li-Fi like Wi-Fi is yet to come. But when further research to supplement the current drawbacks is complete, Li-Fi will light up the fastest era ever.

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