The Development Of The Indoor Visible Light Communication System Based On LED

Visible Light Communication technologies based on LED have the function of illumination,meanwhile, transmitting information through lights have a excellent prospect for application.Nowadays,the development of visible light communication at home is slower than that at abroad.In China, there are not any mature visible light communication systems for commercial use. Thispaper designed a reliable visible light communication system based on white light LED, and besidesit tests and analyzes the properties of the system, and finally, it realized the wireless opticalcommunication between two computers. This paper provides the reference frame and theoreticalvalue for future visible light communication technology research.Firstly, this paper investigates the research status of visible light communication at home andaboard. It introduces the key technologies in visible light communication research. Five differentmodels of LED are used in the research,and the LEDs are CREE-Q5，LTWG，TN-A101, AmericanPURU（I45Mil chip）1w white light LED and certain1W red light LED. It designs the receiving endcircuit and launching end circuit respectively for the system,according to the principals of visiblelight communication system. it analyzes the principal of the circuit and the selection of theparameters, creates the visible light communication system for the experiment,tests the property ofthe launching end circuit. When the signal is in the range of0MHZ to20MHz, the output voltagehas the maximum attenuation of0.8dB,which proves that the property of the launching end isgood.The test to the illumination characters of LED shows that single LED has the availabletransmitting distance of some60cm, and when the distance is becoming longer, it is very obviousthat the illumination attenuate exponentially. The bandwidth tests for the five LEDs indicate that the-3dB bandwidth for the white light LED is generally not large, which is around2MHz. The-3dBbandwidth of High-power red light LED is larger than that of white light LED. This result isapproaching the result of Samsung company research team which shows the bandwidth of whiteLED is2.5M.This paper makes research to the bandwidth of four different models of white lightLED, and the results show the largest one is2.8MHz. After putting a blue filter into the receivingend, the highest system bandwidth reached3.5MHz.But,after research, it shows that after putting ablue filter, the cost for needed power is more larger than the power gained due to the increase of thebandwidth. This paper designs an equalizer circuit, and uses Multisim software to do the simulationresearch, and finally, the bandwidth of the system is improved to7.4MHz,which has exceeded the current maximum level of4MHz by the method of using circuit only. This paper realizes thetransmission of video signal through the visible light transmission system with an equalizer circuit.Finally, this paper realizes the wireless optical communication between two computers with noBit Error, using USB to RS485switch and visible light communication system. And it adds convexlens to the LEDs, as a result of which, the system communication distance is enlarged to sixmeters.