Research On Peak-to-average Ratio Reduction Technique Of OFDM In Indoor Visible Light Communication Systems

In recent years,because of its fast transmission speed,good confidentiality and easy implementation,the visible light communication(VLC)has become one of the hot topics in the field of communication.Because of its high-speed transmission,high spectrum utilization and strong anti-interference ability,Orthogonal frequency division multiplexing(OFDM),as the core modulation technology,has been paid more and more attention in VLC.On the other hand,OFDM will lead to the peak-to-average power ratio(PAPR)problem,which will aggravate the nonlinear distortion of signal in VLC system.Therefore,solving the problem of signal PAPR has become the key to the application of OFDM technology in the VLC system.This paper conducts in-depth research on this key problem,and the specific research contents are as follows:Firstly,the nonlinear model of LED was established,the basic principles of the asymmetric-clipped orthogonal frequency division multiplexing(ACO-OFDM)system in visible light are analyzed,and the definition of the signal PAPR and the probability density function in the ACO-OFDM system are deduced.Secondly,the classical algorithm of reducing the PAPR of traditional OFDM system is applied to ACO-OFDM system.Conjugate symmetry processing is added into the structure of selected mapping(SLM)algorithm and partial transmit sequence(PTS)algorithm to meet the requirements of ACO-OFDM system,and the effect of reducing the PAPR is simulated and analyzed.Then,according to the advantages and disadvantages of each type of PAPR reduction technology,this paper analyzes the combination conditions of the joint algorithm,and proposes the best joint scheme to reduce the signal PAPR.According to the different cascading order in the joint structure,four joint algorithms are proposed:PTS-Clipping joint algorithm,Clipping-PTS joint algorithm,PTS-Companding joint algorithm and Companding-PTS joint algorithm.For these joint algorithms,this paper further simulates and analyzes the system implementation complexity of the joint algorithm,the performance of reducing the signal PAPR,and the performance of the system bit error rate.Simulation and theoretical analysis show that,compared with the single PAPR reduction algorithm,the joint algorithm has a more obvious reduction effect on the signal PAPR.At the same time,when probabilistic technologies and predistortion technologies are combined,the performance of the joint structure in which the probabilistic technologies are processed first and then the predistortion technologies is processed has more advantages.Finally,in order to reduce the complexity of the joint algorithm,for the PTS algorithm in the probabilistic technology,this paper proposes to use the phase factor estimation algorithm as the phase factor optimization scheme of the PTS algorithm,and compare it with the commonly used global search optimization scheme and sub-optimal search scheme.Through simulation verification,the phase factor estimation optimization scheme proposed in this paper is slightly lower than the global search optimization scheme in terms of reducing the signal PAPR performance,but it is better than the sub-optimization search scheme,and in system implementation complexity and system error rate,it has an advantage over the global search optimization scheme and the sub-optimization search scheme.