Research And Implementation Of PAPR Reduction Based On SLM Techniques In CO-OFDM Systems

An Orthogonal Frequency Division Multiplexing?OFDM?system that uses a Coherent Detection method for optical waves is called a Coherent Optical Orthogonal Frequency Division Multiplexing?CO-OFDM?system.It combines coherent detection technology,orthogonal frequency division multiplexing technology and optical communication technology organically,and has strong anti-dispersion ability,strong ability to suppress nonlinear effects,robustness to channel fading,and strong anti-symbol interference.,the spectrum efficiency is high and many other advantages.It has been adopted as a technical standard by many high-speed data transmission systems.However,the problem of a higher Peak-to-Average Power Ratio?PAPR?in a CO-OFDM system is one of its more prominent shortcomings.The high PAPR value problem will increase the operating cost of the system,and will reduce the operating efficiency of the system,and even cause the receiving end to fail to recover the original signal correctly.Based on this problem,this thesis focuses on the PAPR suppression technology in CO-OFDM system,and selects Selective Mapping?SLM?technology with good PAPR suppression performance from probabilistic technology as the object of in-depth study.The research contents are as follows:1.The research work firstly studies the basic theory of CO-OFDM system,and analyzes and discusses the system structure of CO-OFDM.The technical points of CO-OFDM system,the basic principle of the key device Mach-Zehnder modulator,the coherent detection technology used in the system has been studied and analyzed,and the high PAPR problem of CO-OFDM system is discussed.The reason for the high PAPR problem of the system is obtained,and the high PAPR problem in CO-OFDM system is obtained.The problem deserves further study.2.Aiming at the high PAPR problem in CO-OFDM system,starting from the definition and characteristics of PAPR,the PAPR suppression technology in CO-OFDM system is analyzed,and the influence of oversampling technique on the distribution of peak-to-average ratio CCDF function is discussed.In the case of sampling and oversampling,the PAPR value of the Chu sequence is simulated and analyzed,and it is concluded that the oversampling operation can ensure the accuracy of the PAPR of the CO-OFDM signal.Then,the classification of PAPR suppression technology is introduced.It can be divided into three major types of technologies,namely probabilistic technology,distortion technology and coding technology.After analyzing the advantages and disadvantages of each of these three technologies,The SLM technique in the probabilistic class technique does not cause signal distortion and is selected as the object of further research with its superior PAPR suppression performance.3.Aiming at the problem of high computational complexity and poor PAPR suppression performance of traditional SLM scheme,this paper proposes a novel joint improvement method by using the idea of opening the real and imaginary parts of CO-OFDM signals.Low complexity SLM suppression scheme.From the simulation results,the scheme has a computational complexity reduction rate?CCRR?of 50%compared to the traditional SLM scheme and the LC-SLM scheme only when the same number of candidate signals are generated.As above,and the calculation complexity reduction rate increases as the number of sub-block divisions M increases.The simulation results of Matlab show that the PAPR suppression performance of the joint improvement scheme is at CCDF=10^-4,which is about 2.2dB and 0.9dB,respectively,compared with the traditional SLM scheme and the LC-SLM scheme.At the same time,considering that the Clipping technology will bring about certain signal distortion,the system error rate?BER?of the joint improvement scheme is simulated.Through simulation analysis,the joint improvement scheme improves the signal distortion caused by clipping technology to a certain extent,and achieves a good compromise between PAPR suppression performance and system error rate.4.The implementation of the proposed joint improvement algorithm based on SLM technology is studied.An implementation scheme of FPGA-based suppression PAPR algorithm is designed.The modules of the proposed implementation scheme are designed,including the constellation mapping module design using QPSK modulation scheme,algorithm selection module design,selective mapping?SLM?module design,fast Fourier transform module design,and Clipping module design.The ModelSim simulation of the functional structure of each module is carried out.Finally,the FPGA and Matlab joint simulation analysis is used to verify the consistency between the FPGA-based implementation results and the Matlab simulation results.Based on the results of the joint simulation,the FPGA-based results will be used.The implementation results are consistent with Matlab-based simulation results in Matlab,which verifies the effectiveness and feasibility of FPGA-based implementation.