Research On Symbol Detection Algorithm Of SEFDM System

The explosive growth of communication data makes the improvement of spectrum efficiency become a hot spot in the development of wireless communication technology.Spectrally Efficient Frequency Division Multiplexing（SEFDM）uses Faster-than-Nyquist（FTN）technology to compress the subcarrier interval of Orthogonal Frequency Division Multiplexing（OFDM）signals,by introducing artificial inter-carrier interference（FTN-ICI）to improve the spectral efficiency.When SEFDM signal transmits through multipath channel,The coupling between channel interference and FTN-ICI makes SEFDM symbol detection more difficult.This thesis makes the following research on this problem:（1）The interference of SEFDM signal transmitted through multipath channel is analyzed.SEFDM signal transmission model in multipath channel environment is established;the distribution of FTN-ICI is analyzed by equivalent interference matrix;the performance of SEFDM system is compared by defining the ratio of the average power of two kinds of interference.The analysis shows that the effect of FTN-ICI is more significant when the compression factor is less than 0.85,and increases with the increase of carrier number N.（2）SEFDM symbol detection algorithms based on receiver interference processing are studied.Based on the equivalent interference matrix,the performance of the traditional detection algorithms such as zero-forcing detection,Minimum mean square error detection and truncation singular value decomposition is compared.Because of the ill-conditioned equivalent interference matrix,the traditional algorithms can not meet the performance requirements of the SEFDM system.And the greater the N is,the greater the condition number is,the more serious the ill-conditioned is.In order to solve the problem of ill-conditioned interference matrix,an interference cancellation algorithm based on LSQR decomposition is designed,and two iterative detection methods（LSQR-ID and LSQR-Turbo）are used to enhance the performance of the receiver.Simulation results show that LSQR-Turbo can obtain the gain by 4 dB compared with LSQR-ID algorithm when N=64,the compression factor is 0.8 and the bit error rate is 10^-3.（3）SEFDM symbol detection algorithms based on joint interference processing of transceiver are studied.Firstly,the detection algorithms based on Schur decomposition and Tomlinson-Harashima precoding（THP）are designed,Then an improved THP precoding algorithm is proposed in a way of joint processing,that is,the transmitter cancels the FTN-ICI through the improved THP,while the receiver handles the channel effect.The simulation results show that in the case of N=8,the joint processing out performs the Schur decomposition-based detection algorithm and the original THP detection algorithm.A new THP-LSQR algorithm based on matrix decomposition is designed for the SEFDM system with a large number of subcarrier.The simulation results show that when N=64,the compression factor is 0.85,and the bit error rate is10^-4,compared with LSQR-Turbo algorithm,THP-LSQR obtains again of 0.5 dB.