Research On Multi Satellite Cooperative Transmission Technology Based On OFDM In The LEO Satellite Communication System

In recent years, satellite mobile communication has become the most active research area in the field of communication, and has received more and more attention. Satellite mobile communication has been widely used in the fields of international communication, domestic communication,national defense communications and radio and television. The rapid development of communication technology and space technology has created favorable conditions for the further development of satellite communication technology. This paper makes a systematic research on the Doppler shift exiting in low earth orbit satellite mobile communication system, And also focus on multi-link multi satellite cooperation, to solve the general problem existed in the Low earth orbit satellite communication system.In this paper, we first study the Doppler shift phenomenon and the basic principle of OFDM system in low orbit satellite communication system, and provide a system model for the further research of the subject.Then, the performance of the low orbit satellite mobile communication system based on OFDM, including its spectrum efficiency, bit error rate,system user capacity, is analyzed and studied. By using the method of formula derivation and simulation analysis,comparative analysis of the performance of fixed subcarrier interval and adaptive subcarrier interval in OFDM system is carried out,and prove the advantages of adaptive subcarrier interval, which laid a theoretical foundation for the proposed subcarrier interval adaptive algorithm. At last, the relative research status and application of sub carrier interval adaptive algorithm are analyzed,and two new sub carrier interval adaptive algorithms are proposed.The thesis takes the resisting influence of Doppler shift as the starting point, and focuses on the evaluation of system performance from two aspects, such as bit error rate and system capacity. Two new algorithms are proposed, one is subcarrier interval adaptive adjustment based on the bit error rate threshold and the other is subcarrier interval adaptive adjustment based on the maximum system capacity of users. To a certain extent, the two algorithms improve the performance of the satellite mobile communication system, and have certain advantages over the fixed sub carrier interval. Then based on the comparison of the system user capacity simulation is carried out based on the two algorithms, and some preliminary results have been obtained. Subcarrier interval adaptive adjustment algorithm in this paper has certain reference significance for the development of low orbit satellite mobile communication system, and provides a new idea for the development of low orbit satellite communication system based on OFDM.