Research On Phase Noise Mitigation In Faster-Than-Nyquist System

Faster-than-Nyquist(FTN)transmission reduces the symbol interval to improve the transmission capacity and spectral efficiency while preserving the bandwidth.Therefore,FTN has become one of the research highlights in the field of communication in recent years.The phase noise from the radio frequency front-end local oscillator of the FTN system degrades the bit error performance,and couples with the intersymbol interference(ISI)introduced by FTN signaling.The coupling phenomenon makes the conventional phase noise mitigation algorithms for Nyquist transmission where the ISI doesn't exist no longer available.Therefore,the study of phase noise mitigation in FTN system is of highly significance to the practical application of FTN system.To deal with the phase noise in the FTN system,the following work has been done in this thesis:As for the coupled phase noise-ISI interference,the conventional joint mitigation of phase noise and ISI based on the least-mean-square adaptive algorithm is studied.Simulation results show that ISI has significant influence to phase noise processing,and the algorithm is applicable to FTN systems with small compression ratios(i.e.ISI is not severe).Different from the joint mitigation of phase noise and ISI,a phase noise-ISI decoupled FTN system is proposed.At the transmitter side,Tomlinson-Harashima precoding(THP)is employed to mitigate the ISI.Then only phase noise exists in receiver observations.Based on the training pilots,linear interpolation and Wiener interpolation algorithms for phase noise estimation are studied.Aiming at the constellation expansion caused by THP,a phase noise estimation scheme for extended pilot is proposed to decrease the error of phase noise estimation due to the conventional THP modulo operation.The phase noise-ISI decoupling receiving algorithm based on Wiener interpolation outperforms the conventional adaptive algorithm when ISI is not severe,and is applicable to FTN systems with severe ISI.When the roll-off factor of the root raised cosine pulse-shaping filter is0.4,the decoupling algorithm could gain 1.3d B and 3.2d B improvement in FTN system under 256 QAM modulation scheme and FTN acceleration factors of 0.8 and 0.75,and could gain 1.2d B and 3d B improvement under 64 QAM modulation scheme and FTN acceleration factors of 0.8 and 0.75.An iterative FTN receiver under the maximum a posteriori probability(MAP)criterion is proposed.A method for modeling stationary phase noise approximately with first order auto-regressive process is proposed.A reduced complexity factor graph for FTN system is modeled.To reduce the complexity of iteration detection,according to the factor graph,the iterative detection algorithm under MAP criterion based on Gaussian approximation is studied.The iterative algorithm has performance advantage over other algorithms,under low order modulation and low code rate coding scheme.The algorithm could gain 1.3d B and 2.6d B improvement in FTN system under 1/2 code rate coding scheme,64 QAM modulation scheme and FTN acceleration factors of 0.8 and 0.75,compared with the phase noise-ISI decoupling receiving algorithm based on Wiener interpolation.