Research On Channel Characteristics And Transmission Method Of Visible Light Communication

In recent years,with the rapid development of wireless digital terminal market,the amount of wireless data is exponentially increasing.The existing bandwidth resources can not meet the current communication requirement,and the shortage of wireless spectrum resource is becoming more and more serious.At the same time,Light Emitting Diode(LED)technology,with its higher efficiency of electro-optical conversion and longer lifespan advantages,has been widely promoted by governments.Visible Light Communication(VLC)technology based on LED is a new wireless communication technology.Its advantages include huge bandwidth resources,lighting while providing wireless communication service,no electromagnetic pollution,better security,etc.This dissertation mainly focus on the indoor VLC system based on Orthogonal Frequency Division Multiplexing(OFDM)technology.Based on the analysis of the characteristics of the VLC channel,we propose an adaptive OFDM transmission method for VLC,and construct the experimental links based on Field Programmable Gate Array(FPGA)development board for function verifications and performance analyses.In this dissertation,the key components of VLC system,including LED,wireless optical channel and Photo Detector(PD)are introduced and modeled.They determine the communication performance of the VLC system.In order to analyze the performance of VLC system in the electrical domain,we describe the generalized VLC channel,which consists of the frequency responses of the LED,the VLC channel and the PD.Based on the analysis of the generalized VLC channel,we found the Response Mask Invariant Characteristic(RMIC).Then the RMIC is demonstrated theoretically and by means of an experimental system.Based on the RMIC,an adaptive OFDM transmission scheme for VLC is proposed.The scheme is verified by means of experiments.The experimental results show that,the proposed scheme can make better use of the bandwidth resources of wireless optical channel,and it has performance improvements.Finally,this dissertation constructs the VLC transmission links based on FPGA development board.Firstly the design objectives and structures of the links are given.Secondly the key parameters of the links are determined by the analyses and experiments,and the engineering realization of the links is introduced in detail.Based on the link function,we divide the realized links into VLC OFDM baseband link,VLC adaptive OFDM link and VLC OFDM real-time communication link.Thirdly we conduct experimental tests and performance analyses for the links.