Research On Peak-to-Average Power Ratio Reduction Algorithms In FB-OFDM System

Orthogonal Frequency Division Multiplexing(OFDM)technology has the advantages of high Frequency efficiency,strong anti-multipath ability and low implementation complexity.It is widely used in LTE,digital terrestrial broadcasting and other systems.However,OFDM also has problems such as high leakage out of band and strict synchronization requirements,which makes it difficult to adapt to the needs of new scenarios in the future.In order to meet the demand for massive connections of mobile devices in the future,more stringent requirements are put forward on the air interface access waveform,such as higher bandwidth utilization and more flexible multi-service processing capabilities.As a promising waveform,Filter Bank OFDM is suitable for future multi-service systems.However,like traditional multi-carrier,FB-OFDM faces the problem of Peak-to-Average Power Ratio(PAPR).Excessively high PAPR will make the power amplifier work in the nonlinear region,resulting in signal distortion and seriously affecting the system performance.Hence,it is of vital importance to study the PAPR suppression technology of FB-OFDM system.This thesis mainly focuses on the problem of FB-OFDM signal peak-to-average ratio.Firstly,this paper introduces the basic principle of FB-OFDM system,and presents the matrix expression of FB-OFDM for the first time.This new method,which describes FB-OFDM modulation and demodulation in frequency domain as convolution,reduces the complexity of implementation,that is,polyphase filtering structure is adopted to simplify the complexity of implementation at the receiving and transmitting terminals.In addition,the performance analysis of FB-OFDM shows that FB-OFDM can effectively reduce out-of-band leakage and achieve better asynchronous transmission.Secondly,in view of the problem of PAPR existing in FB-OFDM,the Complementary Cumulative Distribution Function(CCDF)of signals sent by FB-OFDM is proposed for the first time in this thesis,and an improved Enhanced Log Companding Technique(ELCT)algorithm is proposed.Given a certain threshold value,the small signal remains unchanged,and the large signal is compressed by ELCT algorithm.The appropriate parameters are selected to reduce the PAPR of the system while taking into account the bit error rate performance.In addition,the autocorrelation of the input sequence is reduced by introducing a precoding matrix at the transmitting end to reduce the PAPR of the system.The effects of discrete Fourier transform matrix,Walsh-Hadamard transform matrix and discrete Hartley transform matrix on PAPR of FB-OFDM system are studied.In order to reduce the PAPR better,the DFT precoding matrix is introduced on the basis of ELCT algorithm,and a Log compression spread(DLCT)algorithm based on discrete Fourier transform is proposed.The simulation results show that the DLCT algorithm has better PAPR performance.Finally,in view of the poor performance of PAPR reduction in the traditional Frequency Domain Spectrum Shaping(FDSS)algorithm,an improved Frequency Domain Spectrum Shaping(CRFDSS)algorithm is proposed to reduce the PAPR of FB-OFDM system by targeted innovation and considering the influence of phase factor.In addition,a new DRRC-CUT filter is designed to optimize the filter of FB-OFDM system,which can reduce the PAPR effect better while taking into account the complexity of system implementation and BER performance.