Research On PAPR Reduction Of Wide-band OFDM Signal Based On Active Constellation Extension

This thesis researched the PAPR Reduction of Wide-Band orthogonal frequency division multiplexing(OFDM)signal based on active constellation extension(ACE).At present,the development trend of the new-generation wideband OFDM system is the increasing of the number of subcarriers and the higher order QAM constellation.To solve this issue,this thesis focused on searching an efficient and novel peak-to-average ratio(PAPR)reduction technology,especially on the ACE method and its joint scheme.Firstly,the basic OFDM system model was described and the reason of the OFDM signal's high PAPR problems was analyzed.By introducing and analyzing the advantages and disadvantages of various PAPR reduction techniques,the ACE method was selected as the key research method in this thesis.The basic principle and mathematical model of PAPR for signal suppression in ACE method were analyzed in detail.Secondly,it can be found that the existing ACE methods have some obvious drawbacks such as high iteration calculation complexity meanwhile a poor PAPR suppression ability for high-order QAM signals for the wideband OFDM signals.An improved pre-distortion ACE algorithm is proposed to simplify the iterative processing so as to reduce the calculation complexity.Different from existing ACE methods,which only extends the outermost constellation points,this proposed algorithm can expand both the inner and outer constellation points at the same time,so the proportion of the scalable constellation points can be increased obviously.Theoretical analysis and simulation results show that the proposed ACE algorithm is able to improve the convergence speed by changing the ACE constellation extension region and optimizing the spreading factor for high-order QAM constellation(such as 256QAM),and to reduce the computational complexity meanwhile.Compared with traditional ACE methods,this proposed ACE algorithm can reduce calculation complexity in the iteration stage effectively.Furthermore,the adaptability of the improved algorithm was also took into accounted.Considering the available PAPR reduction gain of existing ACE methods is limited for the OFDM signals with high-order constellation and large number of sub-carriers.This paper considered the combination of ACE and partial transmit sequence(PTS)algorithms to perform PAPR suppression more efficiently.The basis idea for the combination scheme is that the advantages and disadvantages of the two algorithms should be complementary.After that,a predistortion ACE algorithm with PTS processing(ACE-PTS)scheme is proposed.The pre-distortion ACE has the advantages of fast convergence speed and low calculation complexity,so that the more sub-blocks devision is not necessary for PTS algorithm.Theoretical analysis and simulaiton results demonstrated that the proposed ACE-PTS scheme can obtain an effective PAPR reduction gain for the high-order QAM constellation.Finally,based on the FPGA-AD9361 platform,the proposed ACE algorithm was verified including IFFT module,FFT module,limiting module,constellation expansion module,and the constellation correction module according to its function.The simulation for such modules were performed by using Modelsim.