Research On Nonlinear Distortion Compensation Technology In Visible Light Communication Based On Approximate Message Passin

Visible light communication(VLC)is a new type of information transmission.Compared with traditional wireless communication,it has the advantages of no electromagnetic interference,low cost,high information security,and high spatial reuse,and the visible light band is still a blank and unused spectrum.The visible light band can be used without authorization.However,VLC has problems such as nonlinear distortion and multi-path scattering interference,among which system non-linearity is the main bottleneck restricting the high-speed transmission of VLC.The post-distortion equalizer based on the Volterra series(VS)can effectively alleviate the nonlinear distortion of the system,but this method has the defects of high model complexity and difficult calculation of model coefficients.Therefore,this paper proposes three new nonlinear VS equalizer kernel calculation methods,optimizes the model structure,builds a robust post-distortion equalizer,and then alleviates the nonlinear distortion of the system.The main research contents and innovations are as follows:(1)VLC system model based on DC-biased optical orthogonal frequency division multiplexing technology is modeled.We research the influence of LED transmission characteristics,channel multi-path scattering and other factors on the nonlinear distortion of the system.(2)According to the indirect learning structure,a VS-based nonlinear post-distortion equalizer(VS-NPE)is constructed.Considering the characteristics of a large number of VS-NPE kernels and a large amount of computation,the sparse reconstruction problem that converts kernel estimation into a sparse reconstruction problem,a VS-NPE design method based on regularization adaptive orthogonal matching pursuit(OMP)is proposed,which effectively reduces the number of VS-NPE kernels and improves the efficiency of parameter estimation.(3)We propose a design method of VS-NPE based on support set refined approximate message passing(SSR-AMP),use the improved AMP to correct the sparse support set,thereby improving the estimation accuracy of the VS-NPE kernel.In addition,with the help of state evolution theory,the theoretical expression of the mean square error accompanying the iterative process of the SSR-AMP algorithm in the case of without noise and noise is derived,and the convergence performance of the proposed algorithm is researched.The simulation results show the effectiveness and feasibility of the proposed method.(4)A VS-NPE design way based on stability threshold AMP(ST-AMP)and innovation-adaptive Kalman filtering(KF)is proposed.The method uses ST-AMP to find sparse support sets,and then employs innovation-adaptive KF to estimate the VS-NPE kernel.Compared with VS-NPE based on SSR-AMP,this method has better anti-noise performance under the premise of ensuring the parameter estimation performance.