Research Of Synchronization In Satellite Mobile Communications Under High Dynamic Circumstanees

It is difficult to get synchronization in digital communication,especially in high dynamic environment,great Doppler frequency shift causes the existing synchronization technique hard to apply.Currently,QPSK has been widely used in satellite communication,which is in a high dynamic environment.This paper studies synchronization in QPSK satellite mobile communication system under high dynmamic environment,and its realizatoin on FPGA。The basic theory of satellite mobile communication system is researched in this paper,including the basic principles of modulator and demodulator,and the design diagrams are given.The realization methods of both numerically controlled oscillator(NCO)and the shaping filter are introduced in modulator.When describes demodulation principle,we focus on analyzing the coherent demodulation principle and design ideas.Through inducing the factors,which influence demodulation performance,we obtain synchronous is the key factor that works on demodulation performance.Then,the paper analyses influence of the Doppler effect on satellite communication,and gives the offset parameters of the system.Besides,the paper introduces synchronization schemes commonly used by the current satellite communication systems,and by making an analysis on their respective advantages and disadvantages,an "Trinity" synchronization scheme based on correlation is proposed,which is applicable under high dynamic environment.And explains the design of this synchronization scheme in detail.On this basis,the paper combines the actual communication system metrics,uses verilog in Quartus II development environment to design QPSK modem,the numerically controlled oscillator,shaping filter and synchronization module design processes are also detailedly offered.Through signal TAP Ⅱ tool,we make functional simulation and functional realization for the entire communication system.This paper presents the correlation-based synchronous demodulation method is theoretically able to cope with a mobile satellite communications system with a largeDoppler shift.The method can simultaneously achieve frame synchronization and symbol synchronization,and through adjusting the local unique code waveform,it can be applied to BPSK,8PSK and other modulation methods.So the design owns some theoretical and practical signficance.