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Visible light communication: Let the light and the net in

Oct 09, 2017

With the popularization of smart devices, the network has gradually become a part of people's lives. We know the news through the Internet, check the information, watch movies and so on. At the same time that the network brings great convenience to our life, we are often plagued by problems such as bad network signals, slow Internet access, and WiFi hotspots. It is possible that the emergence of optical communication technology will be able to solve these problems. 

In 2011, Professor , a German physicist, presented a magical invention to science fans at the University of Edinburgh's Ted Global class: He put an LED table lamp next to it, a little device about 30 centimeters below the table lamp, and when he turned on the light, the light shone on the device, The big screen behind him played a video of flowers blooming. Maybe you don't realize how magical it is. And when Professor Haas put his hand between the lamp and the receiver, the video that was playing screeching stopped; when he took his hand off, the video began to play again. At this time all the people present stood and clapped. This is the visible light communication.

Visible Optical Communication (Visible Light Communications, VLC) technology is a new type of wireless communication mode developed rapidly in the past decade, which combines the communication with the indoor illumination source by adding the auxiliary function of data transmission in the public basic lighting facilities, Can construct the indoor visible light wireless communication network, realizes the information from the server arrives the client's wireless transmission. Because the visible light and the daily life are closely related, the office, the family as well as the public place many equipments all contain the visible light source, for example, the Office electric Lamp, the road signal lamp, the square display and so on, so the indoor visible light communication technology can satisfy the user to the mobile communication network coverage scope Provide convenient data service for indoor users anytime, anywhere. At the same time, the indoor visible light communication technology using visible light this special transmission medium, can guarantee the security of mobile communication network, including network data security and user health and security, make the privacy of user information is guaranteed, can't be intercepted by other users, and the user is in mobile communication network for a long time, will not affect their own health. 

With the development of the illumination light source manufacturing technology, the visible-light communication technology which combines the communication function with the illumination function has been paid more and more attention by researchers. Visible optical communication technology can be applied to many occasions, such as home wireless network based on lighting source, high-speed data transmission system in office premises based on basic lighting facilities, data communication system between vehicle and vehicle based on headlight and so on.

The typical indoor visible light communication system mainly includes channel encoder/decoder, digital modulator/demodulator, drive circuit, conditioning circuit, visible light source and photosensitive element. The visible light source and the photosensitive element are the basic devices of the indoor visible light communication system, in which the visible light source combined with the driving circuit can convert the electrical signal to the light signal, realizes the basic illumination function, and emits the visible light which carries the modulation information, the photosensitive element captures the visible light signal, converts it into the light current which can be treated by the back stage conditioning circuit. The digital modulator/demodulator is the key part of the communication function in the visible light communication system, wherein the modulator realizes the control of some characteristics of the light emitted by the visible light source (such as illumination intensity), transmits the original information through the optical signal. The demodulator realizes the function of resuming the information carried from the received signal. The Channel Encoder/decoder is the guarantee of the link reliability and validity of the indoor visible light communication system, which is used to correct the random error and the sudden error in the transmission of the channel, and realizes the correct transmission of the information.

At the transmitter end, after the signal input to the channel encoder, according to the code element Mapping rule code, the coded signal sequence is modulated by a digital modulator, which outputs a continuous modulation waveform and drives the visible light source directly after the driving circuit. At the receiving end, the photosensitive element converts the received optical signal into a light current proportional to the incident energy, and the optical current is modulated into a digital demodulator which is suitable for the signal input of the digital demodulator circuit through the conditioning circuit, and finally recovers the information through the demodulation of the digital demodulator and the decoding of Channel decoder.

As a new technology, our country also attaches increasing importance to the development of visible light communications, March 29, 2012, published on the National Science and Technology department's website, "Twelve-Five" National Science and Technology planning information Field 2013 Alternative Project Solicitation Guide, "Visible light Communication (VLC) System Key technology research" listed as " A separate project under the category of network and communication is designed to develop the new spectrum resources of visible light (wavelength 380nm-780nm), and to study the key technologies such as incoherent optical scattering distortion detection technology, modulation coding, photoelectric multidimensional multiplexing and diversity, best capture detection and so on in the complex channel condition, and establish the experimental system. Transmission rate is greater than 480Mbps, and standard research is carried out. In October 2013, researchers at Fudan University's computer Science and Technology Institute successfully implemented the International Advanced communication Technology, which utilizes the visible light transmission network signals in the house. They connect the network signal to a 1W LED lamp bead, the 4 computers under the light can go online, the maximum rate can reach 3.25G, the average rate of Internet access to 150M.

Of course, as a new network technology and products in the laboratory, visible optical communication technology still has some problems to be solved. For example, there is no dedicated optical communication chipset for the moment, the transmitter and receiver system is very large, the receiver is blocked when the signal will be cut and so on. Nevertheless, visible optical communication, as a complementary technology to WiFi, has broad prospects for development. Believe that the efforts of scientific research personnel, visible optical communication technology will become increasingly perfect, and for our life to provide greater convenience.