When a light is on, the electronic device can be connected to the Internet. Recently, the School of Computer Science and Technology of Fudan University has realized the international advanced communication technology that utilizes the visible light transmission network signal in the house. In the lab, the researchers connected the network signal to a 1W LED bead. The four computers under the light can access the Internet, with a maximum rate of 3.25G and an average Internet speed of 150M. What exactly is Li-Fi? Li-Fi (Light Fidelity) is a new wireless data transmission technology, belonging to the category of Visible Light Communications (VLC). Light, like radio waves, is a type of electromagnetic wave, and the basic principles of propagating network signals are consistent. The researcher puts a microchip on a common LED bulb, controls the change of the LED bulb through the microchip, and encodes the binary data into an optical signal: the light is on and the light is off. Since the frequency is too fast, the human eye is not aware of it, and the photosensor can receive these changes and demodulate them. In this way, the binary data is quickly encoded into a light signal and transmitted efficiently. LED as a semiconductor device, this high-speed light-off, that is, the switching ability of the switch is its characteristic, and the incandescent lamp is very easy to be damaged during the change of the light-off, and the change is too slow, so it does not have this. Communication function. As the most important technology for wireless data transmission, WiFi utilizes radio frequency signals. However, radio waves occupy only a small fraction of the entire electromagnetic spectrum. As users' demand for wireless Internet grows, the available RF spectrum is becoming less and less. Since the available spectrum in the visible light range is extremely wide and the resources are very abundant, scientists can design the Li-Fi wireless network to set the channel width of the communication larger, and the number of parallel channels can be set more. The data transmission speed can be greatly improved. Therefore, research teams in various countries will increase the transmission rate as an important part of the research work, and the maximum transmission rate will be refreshed almost every month. According to Professor Chen Changjun of Jinan University's Institute of Technology, in order to improve the speed of information transmission, many research teams will replace white LEDs with three primary colors or five primary colors, which will weaken the performance of lighting. "The three colors of red, green and blue can really mix the light of various colors, but the lights used for illumination can only display these three colors, so the lamp must be a continuous spectrum, and the lamp with good color rendering must be the full spectrum. In addition, there are a few separate wavelengths." In addition, Professor Chen introduced another way to improve the transmission speed by making efforts in modulation. "We know that the light can transmit 0 and 1 information, flash once. It is a bit, it is a piece of information, but now some research teams use very complicated modulation methods to improve the information transmission rate." But Professor Chen Changjun believes that according to information theory, it will lead to an increase in the error rate of information transmission, so it is necessary The communication distance is limited under the condition that the information accuracy and information amount are satisfied. "Visible light communication, if the LED light is sacrificed as the main function of lighting for speed, then it is likely to go astray." Although Li-Fi technology has been implemented in the laboratory, it still faces many problems. The first thing that needs to be solved is the transmission of light. In communication, when the frequency of electromagnetic waves is lower, the stronger the anti-interference ability and the penetrating ability, the larger the maximum transmission distance allowed. For visible light, because its frequency is hundreds of thousands of times of the electromagnetic waves used by Wi-Fi and cellular networks, its anti-interference ability and penetration ability are greatly reduced compared with the two, as long as it is used between two points. Something blocks these lights, and the transmission of information will stop immediately, not to mention passing through the wall. Haas believes that there are simple temporary solutions. “If the optical signal is blocked and the user needs to use the device to send information, it can seamlessly switch to the RF signal.†But Professor Chen Changjun believes that such switching can be said to be more than one thing. He believes that lighting communication is precisely its advantage. Because it can effectively control the communication range, it is the only advantage that can compete with other means. In order to avoid weaknesses, we can apply them commercially. In addition, Li-Fi relies on visible light for data transmission, and must have light to achieve communication purposes. It is questioned whether it is necessary to turn on the lights if Li-Fi is used during the day. Some netizens exclaimed: "Is it necessary to turn on the light while lying in bed before going to bed?" When the Li-Fi working environment is not only a light source of its own, the ambient light source works in the same spectral band as it does. When the ambient light source is strong, Li-Fi will probably not communicate properly. Therefore, the researchers at Fudan University used the self-developed narrow-band filter in the system to avoid the interference of background light to some extent. For indoor electromagnetic interference, the noise is mainly below 1MHz, and they also avoided this in system applications. Frequency band. Therefore, in order to achieve high-speed transmission speed, more relay stations need to be arranged in the space to ensure the stability of transmission. Another problem with Li-Fi technology is reverse communication. Communication is not one-way. It can only be called communication if there is reception and feedback. Internet access not only requires data download but also data upload. At present, the technology of national research teams can use Li-Fi to download Internet data, but how can data back and feedback be transmitted and the communication link can be smooth? Professor Chi Nan of Fudan University introduced two systems for data uplink, namely visible light uplink and infrared uplink. The so-called visible light up, that is, the need to install a light bulb on the electronic device, while the infrared uplink is invisible to the naked eye, but the rate is low. Professor Chen Changjun is even more outspoken. He believes that it is "this way" for optical communication to achieve Internet access. "Visible light communication is not suitable for two-way transmission of information. If the reverse signal is connected to the Internet, each light must be connected to the Internet. If the signal is sent back, the receiving device should also install the light bulb, and it must be correct, otherwise the speed will not come.†Professor Chen Changjun believes that one-way transmission is more suitable for visible light communication. “We don’t need many places. Information returned, such as television, radio, traffic lights, etc., only need to download information from information sources, such as flight information downloads, advertising information downloads, etc." The core and most practical issue of Li-Fi technology is the chip issue. At Fudan Lab, the researchers used the equipment to have two notebook sizes. In order to shrink the device, the chip must be reduced, and funds need to be supported to support the development of chip technology. The Fudan team pursues the speed, information volume and accuracy of information transmission. Therefore, the power of one lamp cannot meet the requirements, and a very strong light is required as a guarantee. So they focused the light on a point and then collected it with a lens. Some insiders believe that this is “not a light, but a light pathâ€, so as Professor Chi Nan said, the road is still very long. When it comes to the future of visible light communication, Professor Chen Changjun said that there are already commercial examples, such as the positioning system in Korean supermarkets, but still stay at the stage of propaganda models. "Now visible light communication, this little white rabbit is waiting for the turtle, this turtle is not trying to go to the Internet, to replace wifi, but to wait for its unique application. If you can find the characteristics of visible light communication - one-way, medium speed, can The combination of these three points in the control area can really make visible light communication play its huge role." LED lights are an important part of visible light communication. How to make them from the laboratory to thousands of households is the most important problem at present. The requirement of visible light communication for LED lights is mainly based on lighting, or communication, which is still a debate in the industry. However, it is undeniable that the perfection of any new technology is not achieved overnight. Only by breaking through the bottleneck in questioning can we achieve a qualitative leap. Digital Audio,Digital Audio Speakers,Conference Powered Amplifier,Digital Audio Power Amplifier The ASI Audio Technology Co., Ltd , https://www.asi-sound.com
April 07, 2020