Research And Implementation Of OFDM In A Visible Light Communication System

Visible light communication(VLC)technology,as one of wireless optical communication techniques raising in recent years,brings deep fusion of the lighting and communication techniques and has many advantages including low power consumption,and good secrecy.The information in the VLC system was transmitted by modulated visible light emitted by LEDs.With the deep studies of visible light communication,a variety of modulation techniques based on visible light communications have been developed.OFDM,as a multi-carrier modulation technique,is promising due to its high spectrum efficiency and robustness against multipath effects.This thesis focus on the research of the application of OFDM in the visible light communication system.Key algorithms and system performance have been studied by simulation.The feasibility and performance of OFDM in the visible light communication system were demonstrated by off-line OFDM transmission experiment.The main work and innovations of this research are shown in the following four aspects:1.In this thesis,the principle of OFDM modulation technology and in-depth analysis of the basic modules were studied:such as constellation mapping,fast fourier transformation,guard interval and the cyclic prefix.Finally,the OFDM modulation was combined with visible light communication system and DCO-OFDM was proposed as the visible light communication modulation technology.2.In this thesis,the key algorithms of DCO-OFDM technology were studied:such as symbol synchronization algorithm,peak reduction were ratio algorithm,channel equalization algorithm.A detailed research has been done to the influence and relationships of various parameters on the system performance and analysis the key parameters of the system.Finally,after optimized the system parameters and the process of the key algorithm the experiment of the simulation shows that the key algorithm can improve the performance of the system effectively.3.An off-line circuit transmission experimental platform has been constructed in the visible light communication system in order to test the rationality of the complete design of visible light off-line system.Then,on the basis of theoretical analysis,an off-line optical path experiment was set up to measure the performance of optical path transmission so that to find out the deficiencies and the corresonding optimal scheme has been put forward.Finally,the optimized system has been tested and verified,showing that the highest transmission rate of single channel reaches 120Mbps.4.QAM modulation module,Hermitian transform and IFFT module based on the FPGA have been designed and implemented for the OFDM visible light communication system.