Research On Channel Estimation In GFDM Based LEO Satellite Communication Systems

The rapid development of air-space-ground information network and the increase of high-rate communication services places higher demands on the spectrum utilization in the next generation low earth orbit(LEO)satellite communication systems.Compared with Orthogonal Frequency Division Multiplexing(OFDM),Generalized Frequency Division Multiplexing(GFDM)with the advantages of higher spectrum efficiency,lower peak-to-average power ratio and lower out-of-band leakage provides a new idea for signal transmission scheme in next generation LEO satellite communication systems.But the traditional channel estimation algorithms can't achieve the ideal performance in GFDM because of the non-orthogonality of sub-carriers.Therefore,this paper studies the channel estimation algorithm for GFDM based LEO satellite communication systems,and carries out theoretical analysis and simulation verification.Firstly,the basic principles and technical similarities and differences of OFDM and GFDM are introduced,and the implementation of GFDM transmitter and receiver are introduced in detail.Based on the analysis of LEO satellite channel,the system model of GFDM based LEO satellite systems is built,and the performance of GFDM is simulated and analyzed.Subsequently,the traditional channel estimation algorithms in GFDM are studied and analyzed.Focus on the problem of channel estimation performance degradation caused by the non-orthogonality of GFDM sub-carriers,an orthogonal pilot insertion method is proposed based on the characteristics of modulation and demodulation in GFDM.The proposed method can avoid the interference from data symbols on the adjacent sub-carriers.The simulation results show that the proposed orthogonal pilot-aided channel estimation algorithm can significantly improve the channel estimation accuracy.Finally,considering the one-time pilot-aided channel estimation performance is insufficient and the feedback information is not fully utilized,a Turbo receiver for implementing GFDM iterative channel estimation is designed in this paper.By rebuilding the feedback soft information in decoding process into data symbols,the data-aided channel estimation is performed by means of the rebuilding symbols,and the channel estimation accuracy is improved by iteration.Because the inaccurate rebuilt symbols will cause the noise enhancement,a hard decision based iterative channel estimation method is proposed in this paper.Based on the hard decision threshold,the rebuilt symbols can be adjusted to ensure the performance.In order to decrease the iterations and ensure the performance,a soft decision control iterative channel estimation method is proposed.The rebuilt symbols from two iterations can be utilized by soft decision control weight,which can achieve the ideal performance within less iterations.The simulation results show that the proposed algorithm can improve the channel estimation accuracy in GFDM based LEO satellite communication systems and decrease the iterations.