Performance Research And Optimization Of High Spectrum Efficiency Multi-carrier System

Faced with the increasing scarcity of spectrum resources,future mobile communication need to maximize the use of spectrum resources.In recent years,the non-orthogonal transmission technologies,that compress and overlap signals in the time-frequency domain,have higher system capacity and spectrum efficiency than traditional orthogonal transmission technologies.Therefore,the research of high spectrally efficient transmission technology based on the theory of non-orthogonal transmission technology has unfolded.The application of non-orthogonal transmission theory in multicarrier system is more consistent with the future physical layer's demand for spectrum resources.Overlapping-Flitered Multitone(O-FMT)system is a typical non-orthogonal transmission scheme which abandonments the orthogonality between subcarriers of Flitered Multitone(FMT).In this paper,the performance of O-FMT is analyzed and researched,and corresponding optimization schemes are also proposed to deal with the complex network application scenarios in the future,which is of great significance to explore the feasibility of non-orthogonal transmission multicarrier system in improving spectrum efficiency.The specific contents and contributions are shown as follows:1.The performance of the O-FMT system is studied.Firstly the performance of the spectrum efficiency performance is analyzed from two aspects of the calculation and improvement of spectral efficiency.Secondly the anti-frequency offset performance of O-FMT system is mainly studied,by introducing the ambiguity function and by quantitatively analyzing the interference caused by the frequency offset and spectral compressed factor to O-FMT system.The anti-frequency offset performance of OFDM and O-FMT are compared,and the spectral compressed factor limit is obtained.Then aiming at the problem of the frequency offset,a blind estimation scheme suitable for O-FMT systems is proposed and improved to optimize the system.The simulation results show that O-FMT has higher spectrum efficiency than FMT and OFDM systems.Compared with FMT,the anti-frequency offset performance of O-FMT is weaker,which is mainly affected by the overlap between sub-carriers.Compared with OFDM,the anti-frequency offset of O-FMT system is better,as long as the spectral compressed factor is within the range of limits.Furthermore,compared with the traditional frequency offset blind estimation algorithm,the improved new scheme has higher accuracy,anti-interference and anti-fading ability.2.Aiming at the problem of the increasing inter-carrier interference because of introducing overlapping spectrum,an interference cancellation optimization scheme is proposed.Firstly the expression formula of interference filter is deduced theoretically based on the overlapping characteristics between subcarriers in frequency domain,and the inter-carrier interference model and matrix are also obtained.Secondly from the matrix point of view,the inter-carrier interference is eliminated by using THP precoding at the transmitter.Then the O-FMT system is equivalent to the superposition of the traditional FMT system and the inter-carrier interference model system,and the THP precoding scheme is applied to O-FMT system to eliminate inter-carrier interference.The simulation results show that after THP precoding,O-FMT system has lower inter-carrier interference,clearer signal constellation,better performance of bit error rate and achievable bit rate.