撰写With the popularity of smart devices, the network has gradually become a part of people’s lives. We know the news, consult materials, watch movies and so on through the internet. While the network brings great convenience to our life, we are often troubled by problems such as poor network signal, slow internet access and unable to find WIFI hotspots. It can be seen that the emergence of optical communication technology will probably solve the above problems.
In 2011, Professor harald Haas, a German physicist, showed a magical invention to science and technology fans in the TED Global Open Class of the University of Edinburgh, England: he put an LED desk lamp next to him, and there was a small device about 30 cm below the desk lamp. When he turned on the light and the light shone on the device, a video of flowers blooming was played on the big display screen behind him. Maybe you don’t realize how amazing it is at this time. When Professor Haas put his hand between the desk lamp and the receiver, the video being played behind him stopped abruptly. When he took his hand away, the video began to play again. At this time, everyone present stood up and applauded. This is visible light communication.
Visible Light Communications (VLC) technology is a new type of wireless communication mode that has developed rapidly in recent ten years. By adding auxiliary functions of data transmission to public basic lighting facilities and combining communication with indoor lighting sources, an indoor visible light wireless communication network can be constructed to realize wireless transmission of information from the server to the client. Because visible light is closely related to daily life, many devices in offices, homes and public places contain visible light sources, such as office lights, road lights, display screens in squares, etc., so indoor visible optical communication technology can meet users’ requirements for wide coverage and high link quality of mobile communication networks, and provide indoor users with convenient data services anytime and anywhere. At the same time, indoor visible light communication technology uses visible light as a special transmission medium, which can ensure the security of mobile communication network, including network data security and user health security, so that the privacy of user information can be guaranteed and can not be maliciously intercepted by other users, and even if users stay in mobile communication network for a long time, it will not affect their own health.
With the development of manufacturing technology of lighting source, researchers pay more and more attention to the visible optical communication technology which combines communication function with lighting function. Visible optical communication technology can be applied in many occasions, such as home wireless network based on lighting source, high-speed data transmission system in office based on basic lighting facilities, car-to-car data communication system based on car lights and so on.
A typical indoor visible light communication system mainly includes channel encoder/decoder, digital modulator/demodulator, driving circuit, conditioning circuit, visible light source and photosensitive element. Visible light source and photosensitive element are the basic devices of indoor visible light communication system, in which the visible light source combined with driving circuit can convert electrical signals into optical signals, realize basic lighting functions, and emit visible light with modulation information; The photosensitive element captures the visible light signal and converts it into photocurrent which can be processed by the later conditioning circuit. Digital modulator/demodulator is the key part to complete the communication function in visible light communication system, in which the modulator controls some characteristics of light emitted by visible light source (such as illumination intensity) and transmits the original information through optical signals. The demodulator realizes the function of recovering the carried information from the received signal. Channel encoder/decoder is the guarantee of link reliability and effectiveness of indoor visible light communication system, which is used to correct random errors and burst errors during channel transmission and realize correct information transmission.
At the transmitter, after the signal is input to the channel encoder, it is encoded according to the symbol mapping rule. The encoded signal sequence is modulated by the digital modulator, and a continuous modulation waveform is output, which directly drives the visible light source to emit light after passing through the driving circuit. At the receiving end, the photosensitive element converts the received optical signal into a photocurrent proportional to the incident energy, which is conditioned by the conditioning circuit into a signal suitable for the digital demodulator circuit and input to the digital demodulator. After demodulation by the digital demodulator and decoding by the channel decoder, the information is finally recovered.
As a new technology, our country is paying more and more attention to the development of visible light communication. In the Guide for Solicitation of 2013 Alternative Projects in the Information Field of the Twelfth Five-Year National Science and Technology Plan published on the website of the Ministry of Science and Technology on March 29, 2012, "Research on Key Technologies of Visible Light Communication (VLC) System" has been listed as a separate topic under the category of "Network and Communication". The purpose of this paper is to develop new spectrum resources of visible light (wavelength 380nm-780nm), study the key technologies of incoherent light scattering distortion detection, modulation and coding, photoelectric multi-dimensional multiplexing and diversity, and optimal capture detection in visible light communication system under complex channel conditions, establish an experimental system with transmission rate greater than 480Mbps, and carry out standard research. In October 2013, researchers from the School of Computer Science and Technology of Fudan University successfully realized this international frontier communication technology using visible light in the house to transmit network signals in the laboratory. They connected the network signal to a 1W LED light bulb, and four computers under the light could access the Internet, with the highest speed of 3.25G and the average Internet access rate of 150M m..
Of course, as a brand-new network technology and product still in the laboratory, it can be seen that there are still some problems to be solved in optical communication technology. For example, there is no dedicated visible light communication chipset, the transmitting and receiving system is very huge, and the signal will be cut off when the receiver is blocked by objects. Nevertheless, visible light communication, as a complementary technology with WIFI, still has broad development prospects. I believe that with the efforts of scientific researchers, it can be seen that optical communication technology will become more and more perfect and provide greater convenience for our lives.
The video was produced by China, a popular science student, and was authorized to be published in the column "Learning Science with Xiaobian" of CCTV. Please indicate the source for reprinting.
Production: Li He
Producer: computer network information center