卫星物联网中随机接入技术研究进展与展望

卫星物联网具有广域覆盖的特点，可以很好地解决地面物联网的不足。随着海量用户的接入，对接入技术的吞吐量和丢包率提出了更高的要求。目前，以时隙ALOHA及监听信道ALOHA为代表的接入技术在地面得到广泛地应用，但时隙ALOHA在海量接入方面效率低下，不能直接用于卫星物联网，而卫星通信的大传播时延不允许使用监听信道ALOHA。因此，引入干扰消除冲突解决机制的竞争解决分集时隙ALOHA（contention resolution diversity slotted ALOHA，CRDSA）成为新的研究领域。回顾了CRDSA研究进展，从时隙同步和帧同步两个角度将接入技术分为同步CRDSA和异步CRDSA，在深入研究每种技术路线之后，总结了这些接入技术的特点，并以此进行分类概述。其次，详细阐述了每种改进方式的代表性技术原理，并结合技术特点就其在卫星物联网的适用性进行了探讨。最后，分析了未来我国卫星物联网的发展趋势，并结合这一趋势讨论了适用于我国卫星物联网的随机接入技术发展前景。

Research progress and prospect of random access technology in Satellite Internet of Things

Satellite Internet of Things has the characteristics of wide-area coverage, which can solve the shortcomings of the terrestrial Internet of Things. With the access of a large number of users, higher requirements are required on the access technology''s throughput and packet loss rate. Currently, the access technologies represented by time-slot ALOHA and carrier-sensing ALOHA are widely used on the ground. However, slot ALOHA is inefficient for mass access and cannot be directly used in the satellite Internet of Things. The carrier-sensing ALOHA is not allowed because of the large-scale propagation of satellite communication. Therefore, contention resolution diversity slotted ALOHA (CRDSA), which introduces interference cancellation and conflict resolution mechanism, has become a new research field. This paper reviews the research progress of CRDSA and divides the access technologies into synchronous CRDSA and asynchronous CRDSA from the perspectives of time slot synchronization and frame synchronization. After an in-depth study of each technology route, we summarize the characteristics of these access technologies and provide a classification overview. Secondly, the representative technical principle of each improvement method is shown, and its applicability in the satellite Internet of Things is discussed in combination with the technical characteristics. Finally, the future development trend of my country''s satellite Internet of Things is analyzed, and the prospect of random access technology suitable for my country''s satellite Internet of things is considered in combination with this trend.