Research And Improvement Of Visible Light Communication System Based On DCO-OFDM

Visible Light Communication(VLC)has become a research hotspot in the field of wireless communication in recent years due to its advantages of rich spectrum resources,no authorization and good security.DC biased Optical Orthogonal Frequency Division Multiplexing(DCO-OFDM)system is a simple and direct VLC implementation scheme.It has been widely used in VLC because of its high spectral utilization rate and effective resistance to multipath effect.This paper proposes several solutions to the problems of DCO-OFDM based VLC system,such as high clipping noise,high Peak-to-Average-Power Ratio(PAPR)and DC bias optimization.The main research work is as follows:First,a joint improvement method is proposed to solve the problem of high bit error rate in traditional DCO-OFDM system due to the adverse factors such as frequency selective fading,clipping noise and interference.In this method,interleaving technique is applied at the transmitter to reduce the error caused by interference and fading,and the error caused by error detection at the receiver is reduced by iterative optimization of codes with large error.This method improves the error performance of the system with low complexity.Second,aiming at the problem that PAPR is too high in traditional DCO-OFDM system due to OFDM technology,a combined PAPR suppression scheme is proposed.In this scheme,the frequency domain signals are transmitted through a number of interleaving matrices randomly constructed at the transmitting end,followed by IFFT,the frequency domain signals are transmitted through a specific interleaving matrix,and then PAPR is calculated,from which the smallest group is selected for subsequent transmission.This scheme can effectively suppress PAPR and improve the bit error performance of the system.Thirdly,aiming at the influence of DC bias on SNR in traditional DCO-OFDM system,the value of optimal DC bias in DCO-OFDM system under the constraints of total power and channel noise is analyzed.Firstly,the DCO-OFDM transmission signal is modeled as the sum of linear gain signal and equivalent clipping noise.Through theorem,the relationship between DC offset and SNR using single-side zero truncation and double-sided symmetrical truncation is derived respectively.Finally,the simulation verifies that when the total power of the system and the channel noise is constant,there exists a unique optimal DC bias value,which maximizes the SNR of the system.The above methods are simulated by MATLAB,and the effectiveness of the above methods are verified by comparing with the traditional DCO-OFDM system.At the same time,the proposed methods are analyzed from many aspects by changing the conditions of SNR and signal modulation method.