The low earth orbit (LEO) satellite Internet constellation is a hot spot in current global research.And it is highly anticipated that the LEO satellite Internet constellation supports random access to remote sensing satellites and direct on-orbit information processing.However, due to the different orbital heights, the difficult access problems of the bidirectional highly dynamic heterogeneous constellation will be caused.Firstly, the random access scenario under different orbit characteristics and satellite numbers of LEO satellite Internet constellation was set up, and the impact of the spatiotemporal discontinuous visibility and Doppler frequency shift on the remote sensing satellite access performance was focused on.Secondly, based on the characteristics of the random access scenario, the process of on-orbit processing tasks with different delays and the allocation of satellite-ground functions were analyzed.Finally, the problems existing in the current on-orbit intelligent processing algorithm and the focus of future research were expounded, so as to provide reliable theoretical support for the development and applications of LEO satellite Internet constellation and remote sensing satellites in the future.

With the development of the national major project of space-integrated-ground information network including space-based access network and LEO constellation system,it is urgently to be solved how to deal with the routing problem of LEO constellation with inter-satellite communication.One of the research ideas is to study the high dynamic characteristics of LEO constellations and analyze the adaptability of ground-based IP routing technology.The correlation analysis process and conclusion were given,which could provide important basis and support for the routing solution of LEO constellation system with inter-satellite communication.

Considering the issues such as long delay,high code error rate and easily broken links in deep space communications, the concatenation of LT code and LDPC/TPC code is studied and implemented,the principle of LT code and the main implementation method are introduced.The method of LT code concatenating with LDPC/TPC code and the Matlab simulation results are given,which is expected to provide more reliable solution for the acquisition of deep space communications data.

Turbo码具有逼近Shannon容量限的优异性能,介绍了应用于深空通信的Turbo码编码方案和相应的译码算法,并给出了采用修正Max-Log-Map译码算法的深空CCSDS标准Turbo码的软件仿真性能和硬件系统实测性能。通过计算机仿真和硬件实测结果表明,采用该修正Max-Log-Map译码算法的Turbo码译码器易于硬件实现,同时Turbo码仿真性能和实际性能一致,适用于实际工程应用。

The paper presents the importance and prospects of Low Density Parity Check(LDPC) codes for application in deep space equipment.The coding methods used in NASA's all kinds of exploring missions are introduced.The comparison of Turbo and LDPC as well as other coding methods is also given with respect to their roles played in deep space application.Finally,LDPC encoding and decoding methods suitable for deep space exploration are given,and the optimization approaches for the encoding and decoding implementation circuits are provided.

Synchronization is the key technique of DS/FH hybrid communication system. In this paper we propose a scheme of design of frequency hopping synchronization systems. In this scheme, the frequency synchronization is implemented by using the methods of synchronization head message and TOD. The analytical results are given to show that the proposed scheme has better performance of synchronization time and probability of acquisition than other conventional scheme.