Research On Multi-Signal Representation Schemes For PAPR Reduction In OFDM Systems

Orthogonal frequency division multiplexing(OFDM)technology has the advantages of high spectrum utilization,strong inter-symbol interference capability.As a data information transmission technology,it has been widely used in many wireless communication standards,such as wireless local area networks,digital video broadcasting and so on.However,the high peak-to-average power ratio(PAPR)has always been one of the main problems interfering with this technology.In order to solve this problem,many scholars have proposed some valuable methods to improve the PAPR performance of OFDM systems,but these methods all have some defects.In this dissertation,the basic principles of OFDM systems and its PAPR problem are firstly introduced.Based on the current research status of this problem,this thesis focuses on the research of selected mapping(SLM)and partial transmit sequence(PTS)among multi-signal representation methods.The main contributions and innovations are given as follows:1.A threshold classification SLM(TC-SLM)method is proposed to optimize the PAPR performance of OFDM systems.This method first uses two different phase factor sets to generate two candidate signal sets,and then threshold classification technology is introduced to screen and classify each candidate signal set.Finally,the candidate signals selected from the two sets are used to generate more candidate signals through being added and normalized,thereby avoiding a large number of IFFT operations.Compared with the original SLM,TCSLM method greatly reduces the computational complexity while achieving better PAPR performance.In addition,when the similar PAPR performance is obtained,the number of candidate signals actually generated by TC-SLM is much less than that required by the original SLM,i.e.,the proposed TC-SLM can obtain similar PAPR performance with less candidate signals.2.A low-complexity SLM(LC-SLM)method is proposed to optimize the PAPR performance of OFDM systems.This method first uses two orthogonal phase factor sets to generate two PSK modulated time domain signal sequence sets,and then uses these two sets to generate two sets of more QAM OFDM candidate signals,thereby reducing IFFT operations and achieving the purpose of reducing computational complexity.Finally,the QAM OFDM candidate signals are used to generate more candidate signals by being added and normalized without any IFFT operations,which saves the computational complexity further.Simulation results show that compared with the original SLM,the proposed method can not only obtain the similar PAPR performance,but also greatly reduce the computational complexity.3.A grouping and time-domain-sample screening PTS(GT-PTS)method is proposed to optimize the PAPR performance of OFDM systems.This method groups and optimizes all timedomain data sub-blocks,and introduces two new criterias for screening time-domain samples.In the process of generating candidate signals,only the screened time-domain samples need to be weighted,thereby reducing the computational complexity while getting better PAPR performance.Simulation results show that compared with the original PTS and the existing low-complexity PTS,it not only can achieve the similar effect of suppressing PAPR performance,but also significantly reduces the calculation complexity.Finally,this thesis gives the problems that need to be further studied and solved,and the future research work is shown.