Research On Equalization Technology In VLC System Based On OFDM

The visible light communication(VLC)is an emerging wireless communication technique which is used the spectrum of visible light to transmit data,it is a very promising area of research especially in the context of using high-speed switchable LED for data transmission.This technology is a very important supplement to the traditional telecommunications field and brings many advantages as compared to its radio frequency(RF)counterparts.For example,it has an advantage that we can develop large-scale communication system by utilizing existing infrastructure as a transmitter in some places such as hospitals,airplanes and gas stations where the RF communication is limited.In recent years,OFDM has become a dominant transmission technique for VLC systems,with the development of VLC technology.And according to different modulation strategies,it is divided into DCO-OFDM,ACO-OFDM and other methods.However,the system structure is complicated,so that the VLC-OFDM system receives signal distortion.Such complex system still degrades the performance of transmission,and how to improve the transmission rate of the system while ensuring the transmission reliability is an urgent problem to be solved.In order to effectively improve the communication quality of the system without increasing the complexity of the system,in this paper,we propose using improved equalization algorithm in order to overcome the nonlinear influence in the VLC-OFDM system.The proposed method jointly performs the amplitude and phase imbalance.This thesis is summarized as follows.The effects of typical characteristics of the channel on the system are discussed.The influence of stray light and field of view angle on communication distance in communication system is explored,and the relationship between stray light distribution coefficient and communication distance is obtained through experiments.In order to correct the phase deviation caused by nonlinear devices in the system,GSOP method is applied to the VLC-OFDM system considering only phase-induced IQ imbalance,the BER is measured under different phase deviations.Owing to the characteristics of LED,the key parameters of the influence of the LED nonlinear model on the VLC system are discussed,and the third-order nonlinear model is established.The V-I nonlinear characteristics of LEDs were measured experimentally and the nonlinear curve is obtained by fitting.The effectiveness of the blind compensation method based Cordic algorithm against the IQ imbalance is discussed.We further verify the proposed compensation method with QPSK and 16QAM signals respectively.Overall,this paper theoretically analyzes the nonlinear characteristics of VLC-OFDM system,the relevant equalization methods for IQ imbalance is applied.It provides a theoretical foundation and experimental reference for further research on equalization technology in visible light communication.