Study And Application On The Visible Light Communication System Based On White LEDs

With the increasing development of the mobile internet, smart city and other new services, the demand of wireless high-speed communiction is gradually enlarged. However, the wireless electromagnetic spectrum is amost occupied by all kinds of wireless communication technologies. VLC(Visible Light Communication) uses LED(Light Emitting Diode) as its base station and combines lighting with communication as a whole. Compared with the existing wireless radio frequency communication, VLC has many advantages, such as it is environmental friendly, which without electromagnetic interference does' t need to apply for the spectrum resources. VLC is generally considered with a good research value and application prospect. However, there is still a long way to achieve the practical of visible light communication technology. Additionally, the modulation bandwidth of LED is less than 10 MHz. With limited modulation bandwidth, how to expand visible light communication system's bandwidth becomes a key problem to be solved.This paper analyzes the basic principles of visible light communication and operating characteristics of white LED, studies the channel model and then designs and realizes the visible light communication system. The system's communication performance is improved by adding blue light filter, designing light path and introducing the equalization technology. In addition, the research also analyzes the application of visible light communication system based on commercial phosphor LED in special occasions. The main research contents include the following research as:1. Designing and realizing the visible light communication system based on white LED. With white LED and photodetector, it designs a set of visible light communication system and realizes point-to-point data transmission. Through testing transmission of sinusoidal signal for each frequency, it gets the amplitude-frequency characteristic curve and system bandwidth. The experimental results show that the-3dB bandwidth of visible light communication system has reached 2MHz,-10 dB bandwidth has reached 2.7MHz and-20 dB bandwidth has reached 6MHz.2. The experimental system of visible light communication is optimized. Firstly, the optimization of the communication light source of visible light communication system is realized, using the LED array instead of single chip light source. Secondly, the receiving terminal is optimized, in the front of the photoelectric detector filter, blue light filter is added to eliminate yellow light signal which responses lowly. Thirdly, the design and optimization of the optical path of the visible link is done, add the spotlight cup and lens in the channel to increase the receiving sensitivity of photoelectric detector; then, equalization technique has compensated linear distortion of the visible light communication system. Finally, the optimized amplitude frequency characteristic curve of communication system has been tested, the test results show that-3dB bandwidth of the optimized experimental system has reached 41 MHz, which is 20 times before the optimization.3. The application of the visible light communication system are carried out. Firstly, the application of visible optical communication in wireless voice broadcast system has been analyzed, the experimental system is set up, the system test results show that the signal-to-noise ratio reached 40 dB voice in broadcast system. Secondly, the application of visible light communication in text information transmission system has been analyzed, and the experimental system is set up, whose test results show that the bit error rate has reached 10-6. Thirdly, the visible light communication in V2V(Vehicle-to-Vehicle) application of communication system has been analyzed, and the experimental system is set up. The system test results show that V2 V communication distance can reach 3 meters. Finally, the application of visible optical communication in a wireless video monitoring system has been analyzed, and the system has realized the real-time video monitoring function.