Research On The Papr Suppression Algorithm In Visible Light OFDM Systems

Visible optical communication uses the huge bandwidth of the visible frequency range and has many advantages such as low equipment cost,low power consumption,no radio spectrum control,no electromagnetic interference and high confidentiality.The traditional OFDM technique has been improved and applied in visible light communication technology to increase the data transmission rate of the system,but the optical OFDM system has the problem of high peak average power,which limits its system performance and requires measures to suppress its peak-to-average ratio.Therefore,this thesis aims to study the PAPR reduction technology in the visible light OFDM communication system based on the research of OFDM modulation principle and various peak-to-average ratio reduction technologies,and optimize the performance of the communication system.The work in this thesis is as follows:Firstly,the working principle of the conventional OFDM modulation technique is introduced,on top of which the working principle the DCO-OFDM system and the ACO-OFDM system are investigated,and the advantages and disadvantages of these two typical optical OFDM systems are compared through simulation results,and the ACO-OFDM system is identified as the focus of subsequent research.Secondly,the definition of peak-to-average ratio and its distribution as well as the impact of peak-to-average ratio on the performance of OFDM communication systems are specified.Three major classes of typical peak-to-average ratio suppression techniques are briefly introduced,and the advantages and disadvantages of each are compared and analyzed.The principle analysis and simulation have shown that the probabilistic class techniques do not affect the BER performance of the system,so the SLM technique and PTS technique of the probabilistic class are finally identified as the focus of the next step of research.Thirdly,the principle of the traditional SLM（C-SLM）technique is investigated,and an improved scheme of grouped SLM（G-SLM）is proposed to address the problem of high computational complexity of the PAPR reduction scheme of this technique,and aμ-GSLM method combining theμ-law compression expansion method with G-SLM is proposed to further reduce the PAPR of visible OFDM systems in view of the limited PAPR reduction capability of the C-SLM scheme.The simulation results show that the computational complexity of the proposed method has been significantly improved,and with the increase of the number of candidate signals,the degree of improvement is more obvious.When the CCDF value is 10^-3,the proposedμ-GSLM method compared with the original OFDM signal,G-SLM alone andμ-law compression extension method alone,the PAPR is reduced by 7.5d B,3.2d B and 2.1d B,respectively.Fourth,the principle of the conventional PTS technique is investigated.To address the problems of high computational complexity and low efficiency in searching for the optimal phase rotation factor,a unipolar optical OFDM（UO-OFDM）system without Hermitian symmetry is used,while the GA-PTS algorithm is proposed and applied to the UO-OFDM and ACO-OFDM systems.Simulation results show that the GA-PTS technique greatly reduces the time required to search for the optimal phase rotation factor;and that the GA-PTS algorithm based on the UO-OFDM system performs better than the GA-PTS algorithm based on the ACO-OFDM system.