Research And Verification Of The Key Technology Of Time And Frequency Synchronization Of Satellite TT&C Link

The establishment of a complete satellite TT&C network is one of the important reasons for the development of aerospace industry.No matter national navigation system,or meteorological remote sensing system,they all belong to TT&C systems With its excellent anti-jamming capability,direct sequence spread spectrum has always been the first choice for TT&C link communication.As a prerequisite for the accomplishment of the scheduled monitoring and control functions,it is critical to complete time-frequency synchronization of the spread spectrum signal.However,the special communication environment and external conditions have brought about two effects on the received signal: the long communication distance and the bad channel make the received signal power greatly attenuate,the signal to noise ratio is extremely low;the high dynamic characteristic of the satellite makes the received signal's doppler effect worse.If the received signal is not accurate time-frequency synchronization,the entire business will face failure.For this reason,the thesis focuses on the key technology about time-frequency synchronization of star-based monitoring and control link with direct sequence spread spectrum,which mainly includes:For the synchronization of time,it requires 5s and the doppler frequency offset is up to ±150kHz,the three methods of investigating pseudo-code capture are selected to combine the fast capture of pseudo-code based on FFT with doppler frequency offset onedimensional search.Differential coherent integration 45 times to improve the signal's noise ratio.By pre-compensating the received signal first frequency offset,and then an FFT operation with an IFFT operation and differential coherent integration 45 times after the decision,4.515 s to complete the capture.Second,for the pseudo-code phase jitter,according to the classic code tracking loop proposed a 5-way parallel pseudo-code tracking loop design.Through the five branches were set to different pseudo-code phase,taking the largest branch of the correlation value as the best sampling branch,complete pseudo-code phase tracking,precision up to 1/4chip.Third,for the doppler frequency offset pre-compensation residual frequency offset,Costas PLL is used for phase difference tracking and compensateing.Accomplish the program design Simulink simulation.Fourth,based on the software radio platform,to complete the star control link highprecision time-frequency synchronization key technology validation.FPGA chip as the main device,Verilog as a programming language,to achieve synchronization key technology on the board test,the module with a good,to complete the established function.This thesis explores and validates the key technology of time-frequency synchronization of satellite TT&C links under specific conditions.The research results have been realized and tested,which is of practical value and can provide reference and support for the construction of satellite monitoring and control network in China.