Study On Visible Light Communication System Based On LED Illumination System

Light emitting diode (LED) is one of the most promising green solid light sources in the twenty-first century. Compared to traditional light sources, LEDs not only have less power consumption, longer life, smaller size, better for environmental protection, but also possess advantages of shorter response time and much better modulation capability. The visible light communication (VLC) technology based on LED illumination system is a novel wireless optical communication method using the visible light as information carrier wave, where optical signals travels directly in the air, without using optical fiber as the transmission medium. So both the illumination and communication functions are perfectly unified. Just replacing traditional light bulbs by LEDs, the illumination units can be converted to wireless network transmitters. As a result, the VLC technology and its applications are attracting more and more attention under the current background of green low-carbon economy.In this thesis, the development and current research status of VLC, as well as the key techniques of realizing VLC, are introduced firstly. The optical and electrical properties of LED used in the visible light transmitter are discussed, and the unmeasurable characteristics of bright-state capacitance of LED is analyzed. Then, the spatial distribution model of LED light intensity is established by using Matlab, which provides a theoretical basis for the LED array used in the VLC system. By the derivation of channel model, VLC is proved a possible technology for wireless communication system. The research and design of visible light transceiver are the focus of this thesis. The LED drive circuit and the amplitude equalizer in the VLC transmitter are designed, and the properties of PIN phote-detector and the transimpedance amplifier are studied. The transfer function of VLC system is derived, and the electrical-level threshold judger under the OOK modulation mode is designed. In order to evaluate the VLC link, a testing platform is established, in which the real-time control and sampling of the function generator and oscilloscope are realized by LabVIEW programming. The testing results indicate that the bandwidth of VLC system is basically not affected by the ununiform spatial light intensity distribution of large-power LEDs.Using the intensity modulation and direct detection method, a VLC transceiver path is successfully established with the 3-dB bandwidth of about 7 MHz. Finally, a novel wireless navigation system based on VLC technology is proposed. A bit-error-rate testing platform based on the OOK modulation and Manchester codec is designed by using FPGA development kits. The function verification experiments of the navigation system are then completed. The effective range of visible light identification based on low power LED (300 mW) can be extended to 3 meters using the designed visible light transmitter optical lens and the terminal electrical-level judger. Furthermore, a new broadband system combining VDSL with VLC is tentatively proposed. The preliminary communication speed up to 41 Mbps is obtained, which may provide a new way for the next generation wireless broadband access.