Research On PAPR Reduction In Multicarrier Wireless Communication Systems

Due to advantages of high spectral efficiency and robustness to multipath fading,orthogonal frequency division multiplexing(OFDM)has already been adopted by many wireless communication standards.At the same time,OFDM technology also has some shortcomings,such as OOB(out of band)radiation is high,and it is sensitive to frequency offset and time offset.In view of these shortcomings of OFDM technology,some new multicarrier technologies with better performance have been proposed,among which the generalized frequency division multiplexing(GFDM)technology is a representative technology.GFDM has low out of band radiation power,flexible use,and high time-frequency focusing property.It is a potential alternative technology of OFDM and is expected to be applied in the future broadband high-speed wireless communication system.However,one of the common problems of multicarrier systems is the high PAPR,which has a serious impact on BER performance of the systems and efficiency of HPA.At present,the existing PAPR reduction algorithms still need to be further improved in algorithm complexity,OOB radiation suppression,BER performance and other aspects.In view of the shortcomings of existing PAPR reduction technology,this paper improves these algorithms.The innovative work mainly includes the following three aspects:Firstly,in this thesis,a nonlinear companding algorithm based on tangent linearization processing for PAPR reduction in OFDM systems is proposed,and at the same time,the OOB radiation of the signal is suppressed as much as possible.Different from the existing PAPR companding algorithm based on PDF function adjustment,a new PDF function with continuous differentiability is designed.The original PDF is cut off for PAPR reduction,and lower and medium segments of original PDF are scaled and linearized respectively,for maintaining power and cumulative distribution constraints.The linearized segment is set to be the tangent of the scaled version at the inflexion point,so as to reduce the out-of-band(OOB)radiation as much as possible.Based on the adjusted PDF function,a new nonlinear companding function is derived.The designed scheme can produce low OOB radiation.In this paper,under the joint constraints of power conservation and probability conservation,the solution method of the parameters of the companding function is analyzed and given.At the same time,the theoretical value range of the maximum amplitude of the signal after companding is derived,which is helpful for the reasonable selection of parameters in practical application.In order to improve the BER performance of the system,a new receiving method based on interference cancellation is proposed.Simulation results indicate the proposed scheme can achieve bet-ter OOB radiation and BER performance at same PAPR levels,compared with existing similar companding algorithms.Then,a nonlinear companding algorithm based on PDF scaling is proposed to reduce the PAPR of OFDM signal.Generally speaking,the closer the PDF of the signal after companding is to the PDF curve of the original signal,the smaller the distortion of the signal caused by companding,and the lower the OOB radiation of the signal after companding.The proposed algorithm fully considers the statistical characteristics of the original signal and combines it with the amplitude limiting theory.By expanding the PDF curve of the original signal,the small amplitude signal can be appropriately amplified to a certain extent,and the final truncation processing can ensure that the PAPR of the companded signal is within the required range,so that the signal with the amplitude greater than the cut-off value is compressed.Different from other companding algorithms based on PDF function adjustment,this algorithm has no segmented processing operation,which is conducive to lower OOB radiation of the signal after companding;moreover,the companding function is simple in form.The proposed algorithm has a larger parameter adjustment range,which can meet more actual needs.Simulation results show that the scheme can effectively reduce the PAPR of OFDM signal.Compared with the existing companding algorithm,under the same PAPR performance level,it has ower OOB radiation.Finally,m-SLM algorithm,an improved SLM algorithm,is proposed to reduce the PAPR of GFDM signal.GFDM system is a non-orthogonal carrier system based on cyclic block structure.There is an overlap between GFDM symbols,thus,when we select the best phase of GFDM symbols by SLM algorithm,we must consider the influence of other symbols.If we take all the influences of symbols into account,the amount of computation will be quite large,thus,we only consider the influence of the previous symbols,so that we can improve PAPR performance without increasing complexity.The improved SLM algorithm fully considers the overlap of GFDM symbols in time domain and optimizes the penalty function for calculating the optimal phase.Compared with the traditional SLM algorithm,the complexity of the algorithm is the same,but the PAPR performance is greatly improved.