Abstract
Low-Earth-Orbit satellite access network (LEO-SAN) can realize real-time and three-dimensional broadband access on the earth anywhere and any time. It has become a major development trend of satellite Internet and mobile communication networks, and has attracted more attention and research from academia and industry. LEO satellites can achieve global coverage through giant constellations. Compared with medium- and high-orbit satellites, LEO satellites have larger communication bandwidth and shorter communication delay, and they are becoming an integrated part of future 6G mobile communication networks. Many countries in the world have planned for LEO satellite constellations and spectrum allocation to support the process of implementation. Differing from traditional terrestrial access networks, LEO-SAN faces many challenges including high-speed mobility of space base stations and highly limited communication and computing resources. LEO satellite constellations are in large scales, where the costs of network management, maintenance, and control increase rapidly. In addition, the high-speed movement of LEO satellites makes the network topology change rapidly, which causes frequent handover for user terminals. Moreover, the beam overlaps between satellites changes with time, resulting in potential interference. In response to the these challenges, researchers have carried out research in the areas including network architecture, beam coverage, resource management, etc. However, the research on LEO-SAN is still in its early stage, and more research is needed for development of comprehensive and systematic theoretical methods and technical standards.