Research On Nonlinear Distortion Compensation Technology In Visible Light Communication System

With the ever increasing in the amount of data transmitted on the network,the spectrum resources used by wireless radio frequency communication have become progressively tense,thus as a new communication method,visible light communication(VLC)has gradually attracted people's attention.However,the presence of nonlinear devices,especially light-emitting diode(LED),can cause nonlinear signal distortion in VLC system,which severely affects the system performance.Therefore,it is necessary to study the nonlinear signal distortion compensation algorithm.In this thesis,based on the above background,the common VLC system model,LED model and channel noise model are introduced briefly,and then the impact of LED nonlinearity on the signal is simulated and analyzed,meanwhile,according to the nonlinear characteristics and memory effect of LED,the nonlinear distortion compensation algorithms of signal at the receiver side are studied.The main innovations are as follows:(1)One post-distortion compensation scheme based on the sparse kernel affine projection algorithm(KAPA)is explored.Based on the related properties of the reproducing kernel Hilbert space(RKHS)and the kernel technique,the sequential learning criterion of the KAPA is derived in detail,and the sparse KAPA is proposed to compensate for the nonlinear distortion of signal.(2)Aiming at the memory effect of LED,a memory effect depression algorithm is proposed,which is combined with sparse KAPA to mitigate signal distortion.Simulation results show that the sparse KAPA has faster convergence speed and better system performance than the kernel least mean square algorithm.In addition,when the memory effect depression algorithm is combined with the sparse KAPA,the floor effect of the algorithm can be reduced effectively.(3)Another post-distortion compensation scheme based on radial basis function(RBF)interpolation and memory effect depression is analyzed.Firstly,the principle of RBF interpolation is described in detail through the simulation illustration.Then it is suggested to utilize RBF interpolation combined with the proposed memory effect depression algorithm to reduce the signal distortion caused by the LED.The simulation results present the effectiveness of the algorithm based on RBF interpolation and memory effect depression,and whether the memory effect of LED is removed or not can also make the bit error rate(BER)of the system achieve better performance.