Research On Homodyne Frequency Acquisition Technology Based On Orbit Prediction In Satellite Optical Communication

Satellite optical communication is a space optical communication technology.Compared with traditional microwave communication,satellite optical communication has many advantages.With the development of science and technology,the demand for satellite communication rate is increasing.Compared with direct detection,homodyne coherent detection has higher signal-to-noise ratio,and the improvement of signal-tonoise ratio is conducive to further improve the communication performance.However,in inter-satellite optical communication,the relative motion between satellites will cause Doppler shift of the signal light received by homodyne detection,and the frequency drift of the signal light will seriously affect the performance of homodyne coherent optical communication systems.Aiming at the problem that the signal optical frequency drift needs to be captured,it is of great significance to study how to establish a homodyne frequency capture model.First,this paper summarizes and analyzes the current research status of frequency acquisition technology.To deal with the problem of excessive initial frequency difference,temperature tuning is generally used for coarse acquisition,but because the temperature tuning speed is too slow,the frequency acquisition time will be greatly increased.By analyzing the characteristics of Doppler frequency shift in inter-satellite optical communication,it is found that estimating and pre-compensating the Doppler frequency shift can greatly shorten the frequency acquisition time.Therefore,the research in this paper is based on the orbit prediction Doppler frequency shift and precompensation,and gives a homodyne frequency acquisition scheme.Secondly,this paper establishes a simulation model of homodyne coherent optical communication system,derives the average output voltage expression of the XOR phase detector based on I branch delay,and proposes a closed-loop acquisition scheme based on orbit prediction.The phase discrimination,frequency discrimination characteristics and frequency acquisition performance were simulated and analyzed.Finally,this paper proposes an algorithm acquisition scheme based on orbit prediction,and establishes a simulation model of the frequency offset estimation algorithm.The effects of signal-to-noise ratio,line width,frequency estimation block length N and phase estimation block length M on the acquisition accuracy are analyzed.Simulation results show that the algorithm model eliminates the effect of frequency drift.