Research On PAPR Reduction Based On Linear Companding Transforms In OFDM Systems

Orthogonal frequency division multiplexing(OFDM)technology is one of the core technologies of the long term evolution(LTE)/5th generation(5G)because of its high spectral efficiency and anti-multipath fading,and is an important candidate technology of the future broadband wireless communication system,such as 6th generation(6G).High peakto-average power ratio(PAPR)is an inherent problem in OFDM systems.When high PAPR signal passes through the high power amplifier(HPA),signal distortion is introduced and the efficiency of the power amplifier is reduced.At present,the energy consumption of base stations is one of the challenges in the industry.Facing to "dual carbon strategy",high efficiency and green is an trend of 5G and even the future 6G communication.Therefore,it is of great significance to study and optimize PAPR reduction techniques to ensure the performance and low energy consumption in system.Many PAPR reduction techniques have been proposed to reduce PAPR.Among them,linear companding transform(LCT)is more suitable for practical application due to its low complexity.However,the existing LCT has problem of poor bit error rate(BER)performance or high out-ofband(OOB)radiation,which needs further improvement.Therefore,designing LCT scheme with good performance is a key to solve the energy consumption problems of future broadband high-speed wireless communication,and is important for theoretical and practical application.In this thesis based on the analysis of the existing typical PAPR reduction techniques,continuous piecewise linear companding function is proposed which extends the function form of companding scheme.This thesis focuses on the design of continuous piecewise linear companding scheme,and the main work content and innovation results are as follows:Firstly,a continuous piecewise linear curve fitting(CPLCF)method is proposed based on continuous piecewise linear companding function.This method uses continuous piecewise linear function to fit the prototype nonlinear companding function,which can achieve almost the same performance as the prototype nonlinear companding scheme with lower complexity.The method provides a solution for problem that nonlinear companding transform with good performance is difficult for application,because of its high complexity,and makes up for the performance gap between the nonlinear companding and linear companding schemes.The method provides a new way to explore and design the LCT scheme.In addition,with proposed design method,three NCT schemes are used as templates to design linear companding function,which verifies that the design method can be applied to all nonlinear companding schemes.Secondly,the thesis provided generalized continuous piecewise linear companding scheme with four constraint optimization problem including the minimum companding distortion,minimum noise influence,hybrid optimization of companding distortion and noise influence,the minimum distortion of probability density function.The value range and effect to performance of main parameters were analyzed.The performance relationship among different optimization is compared.Compared with previous design method,this method has great flexibility in performance adjustment and is not limited by the prototype nonlinear companding function.The proposed scheme has better performance than the current typical linear and nonlinear companding scheme.Moreover,by adjusting parameters flexibly,the performance among PAPR reduchtion level,BER and OOB radiation can be flexibly adjusted.In addition,an iterative receiving method is designed to further reduce the BER of the receiver.Finally,the thesis summarizes the whole work and looks forward to the next step.