Research On Non-Stationary Signal Waveform Design And Synchronization Technology Of Satellite

Satellite communication plays an important role in today's data age because of its wide coverage and large communication capacity.With the wide application of satellite communication technology,its security has also been highly concerned.Because of the openness of satellite communication channels and the poor concealment of communication signals,the enemy can easily intercept and decipher useful information,which is very dangerous,so it is urgent to improve the security performance of satellite communication.At present,for the problem of information interception by non partners,the most commonly used method is spread spectrum to improve the security of information.Due to the problem of low probability of intercept(LPI)signal detection,along with the in-depth study,the security of traditional spread spectrum has also been severely challenged.Therefore,it is difficult to ensure the anti interception performance just by spreading the signal simply.We have to consider other aspects to improve the security of the information.In this thesis,the spread spectrum technology as the main body of the non-stationary signal waveform design from the time domain,code domain,frequency domain,modulation mode four aspects,increase the complexity of the signal to improve its anti interception performance.At the same time,because the satellite mobile communication system is in a high dynamic environment,there is a great relative motion speed between the sender and the receiver,which will make the signal received by the receiver have a large Doppler Shift.There exist demodulation problems of the signal at the receiving end.Therefore,how to overcome the Doppler frequency shift and realize the satellite ground synchronization in the high dynamic environment is an important research direction at present.This thesis analyzes the harm of Doppler shift,introduces some Doppler shift estimation algorithms used at present and their performance.Finally,a PMF-FFT acquisition algorithm combined with segmented matched filter(PMF)and fast Fourier transform(FFT)is used to realize the signal synchronization.The simulation performance of PMF-FFT acquisition algorithm is analyzed and improved,which makes the improved PMF-FFT algorithm have very good acquisition performance.