Research On Frequency Offset Estimation Technology Of Broadband Satellite Link

Satellite communication systems have the characteristics of large coverage area,low transmission delay,flexible deployment,and freedom from natural disasters.They often provide services for military and civilian users together with ground mobile communication systems such as 4G and 5G.The current research hotspot is also the future development trend.Compared with medium-orbit and high-orbit satellite communication systems,low-orbit satellite communication systems have many advantages,such as lower operating orbits,lower propagation delays,lower path losses,etc.,and only need dozens of satellites to achieve global coverage.However,the relatively large relative motion speed between the low-orbit satellite and the terminal will bring about a large Doppler frequency offset,especially in the millimeter wave frequency band,the Doppler frequency offset will reach 700kHz.Therefore,after the receiver antenna receives the signal,it needs to do frequency offset estimation and compensation at the physical layer,otherwise the demodulation performance of the system will be very poor,and the bit error rate may be as high as 0.5.Orthogonal Frequency Division Multiplexing(OFDM)system has been widely used in 4G,5G,DVB and other systems due to its extremely high information transmission rate,high spectrum utilization efficiency and very flexible subcarrier allocation scheme.However,the OFDM system is more sensitive to the carrier frequency offset,and a large Doppler frequency offset will cause severe inter-subcarrier interference.Therefore,this paper mainly studies the application scenarios of low-orbit broadband OFDM satellite communication systems.Slice Doppler frequency offset estimation algorithm.This paper first expounds the research background of the subject,the organization structure of the paper,and the research status of the frequency offset estimation algorithm at home and abroad.Then,some knowledge of OFDM system is described,including mathematical model,flow chart,key technologies,advantages and disadvantages,etc.,and the influence of normalized frequency offset on bit error rate and effective signal-to-noise ratio of OFDM system is studied.Finally,the low-orbit satellite frequency offset estimation algorithms are divided into the following categories for research:data-aided frequency offset estimation algorithms based on training symbols or pilot symbols,frequency offset estimation algorithms based on ephemeris information and satellite Doppler characteristics,and signal-based frequency offset estimation algorithms.Structural properties such as cyclic prefixes or blind frequency offset estimation algorithms based on signal subspaces.For the data-aided frequency offset estimation algorithm based on training symbols and pilot symbols,this paper focuses on the classical P.H.Moose algorithm,Schmidl&Cox algorithm and Molrelli&Mengali algorithm,and compares their complexity and frequency offset estimation range.In view of the advantages and disadvantages of these algorithms and the Doppler frequency offset of the low-orbit satellite communication system,this paper proposes a two-stage Doppler frequency offset estimation algorithm,which first uses the geometric relationship between the terminal and the satellite to establish the coordinates The Doppler frequency offset calculation formula is derived,and the Doppler frequency offset calculated in the formula is pre-compensated,and then the Molrelli&Mengali algorithm is used to perform more precise frequency offset estimation and compensation.Finally,the link-level simulation platform is used.It is one of the innovations of this paper to verify the performance of the proposed algorithm.For the blind frequency offset estimation algorithms that do not require data assistance,this paper mainly studies the maximum likelihood estimation(ML)algorithm,the MUSIC-like algorithm and the ESPRIT-like algorithm based on the subspace method,and the ML algorithm needs to use the information of the cyclic prefix.In view of the advantages and disadvantages of these several blind frequency offset estimation algorithms,this paper proposes a two-level Doppler blind frequency offset estimation algorithm suitable for low-orbit satellite noncooperative communication systems,and verifies the proposed algorithm on a link-level simulation platform.The performance of the algorithm,which is another innovation point of this paper.