Research On The Algorithm Of Carrier Frequency Offset Interference Cancellation Based On OFDM

Low-orbit satellite communication system has become a very important part of the mobile communication system.It has the characteristics of global coverage which cannot be achieved by ground communication,and it can achieve the user's fast communication service anytime and anywhere without the influence of the environment.However,the low orbit mobile satellite communication system has limited bandwidth,which limits its bandwidth utilization.Using the characteristic of Orthogonal Frequency Division Multiplexing(OFDM)can not only increase the band utilization of the system but also resist Frequency selective fading effectively.However,OFDM transmission technology cannot solve the doppler frequency shift caused by the rapid motion of low-orbit satellites.Therefore,the carrier-frequency offset interference elimination algorithm of OFDM in low-orbit satellite mobile communication system is mainly studied.Firstly,the performance of the low orbit satellite system is analyzed.The influence on OFDM transmission technology is described from two aspects of Additive White Gaussian Noise(AWGN)and doppler frequency offset characteristics respectively,which lays the foundation for the research on carrier frequency offset interference elimination algorithm.Secondly,by comparing different carrier frequency offset pre-elimination algorithm,an improved carrier frequency offset pre-elimination algorithm is proposed.The algorithm takes Chu sequence as pilot frequency and it distributes pilot frequency evenly in OFDM symbol.Moreover,it combines Moose elimination to capture faster,more accurate,and more stable estimates over a range at the expense of increased computation.Finally,for the error between the estimated value and the exact value after the pre-elimination and the interference problem brought by AWGN,Frequency Domain Recursive Least Square(FD-RLS)is proposed after the comparison of different carrier frequency offset precision elimination algorithm.The algorithm not only has better performance of eliminating,but also can follow time-varying channel,which is more suitable for low orbit satellite system.The performance of the system is improved by combining the algorithm with the DFT time domain frequency offset precision elimination technique.