The Research Of Synchronization Technology In GMR Satellite Communication System

With the development of science and technology, the satellite communication technology has become an integral part in the field of communications, it compensates for the inadequacies of terrestrial communication systems effectively,people pay more and more attention to it. The satellite communication systems have very large covering area, a far communication distance, high communication quality and reliable system. They have been widely used in military communications and civilian communications.In the process of GMR(GEO-geostationary earth orbit Mobile Radio) system's demodulation, we need to get the optimal sampling time through symbol timing synchronization, and carrier synchronization is a prerequisite to the coherent demodulation. The timing error and carrier frequency offset will bring great influence to the system's performance. It is very important to design a synchronization scheme which has good performance for the satellite communication system. It is valuable to research the algorithm of synchronization parameters' estimationIn order to design a synchronization scheme for the GMR system, this paper has researched the relevant theories of synchronization and analyzed the maximum likelihood estimation theory about estimation of timing error and carrier frequency offset, and researched the receiver structure and process of the burst.On the basis of theoretical research, this paper has designed synchronization scheme for the GMR satellite communication system. The details are as follows:(1) This paper researched the performance and the key technologies for the demodulation of GMR system, and designed the demodulation scheme.(2) This paper researched feedforward and feedback algorithms of timing detection and designed the scheme of timing recovery. This paper has designed the interpolation filter, timing controller, loop filter and timing error detector. This paper proposed an improved Gardner algorithm to solve the problems of big timing error and noise in the timing recovery system. The results of simulation proved the improved algorithm is effective.(3) This paper researched the frequency offset estimation algorithm, analyzed advantages and disadvantages of the present algorithms. An improved algorithm is proposed in order to estimating the Doppler shift. This paper used two steps idea: the coarse estimation algorithm is based on FFT, the fine estimation algorithm is achieved through interpolation in frequency domain. The simulation results showed that the improved algorithm can estimate Doppler shift, and it has a large estimating range and high accuracy.(4) This paper researched the carrier phase estimation algorithm. After the frequency estimation, we used V-V algorithm to estimate the phase. The simulation results showed that this algorithm has good performance in MPSK system, and the SNR has little influence to it.