Availability Of Equalization Schemes Of Visible Light Communication Receiver

By using light emitting diodes for both illumination and data transmission,visible light communication(VLC)has become the research focus in recent years.Distinct advantages including the abundance of unregulated bandwidth,environment friendly and without existing radio frequency interfere make VLC a competitive method in optical communications.Due to the received signal consisted of direct light and multiple reflective lights,the ISI caused by the multipath delay when signals are transferred to the destination by different paths takes place.This paper introduces a series of research on equalization method to overcome ISI,so as to improve the performance of VLC systems.Firstly,this thesis introduces the research background,research significance and lists the innovation and research content of this paper.Secondly,the thesis analyzes the structure of VLC systems and multiple-bounce impulse response,then characteristics of optical wireless channel is studied and it is shows that ISI has large influence on system performance.Thirdly,considering the time-variant and multipath characteristics of VLC channel,this paper describes the principle of time domain equalization and adaptive equalization technique.Then the following content gives the focus research on the least mean square(LMS)algorithm,which is a key point in this paper.Based on the contradiction between the fast convergence rate and low steady state error of fixed step size LMS algorithm,an novel variable step LMS algorithm is proposed,which makes use of the gradient of error signal to control the new variable step size.Computer simulation results show that the proposed algorithms mark improvement compared with other similar algorithms.Finally,blind equalization technique is studied,because constant modulus algorithm(CMA)is very sensitive to the initialization and the convergence speed is slow,an initialization scheme for CMA based on received signal power is proposed.Computer simulation results show that the proposed scheme can effectively reduce the residual ISI and accelerate the convergence speed.