Non-Terrestrial Networks in 6G on Standardization, Key Technologies and Challenges

The efforts on the standardization of Non-Terrestrial Networks (NTN) make satellite communication play a pivotal role in 6G era. The integration of satellites and terrestrial networks (TN) provides ubiquitous coverage of 6G coverage. This paper comprehensively investigates the progress of both standardizations and industry construction of satellites. In particular, the focus is on the prospective key technologies of flexible architecture, coverage enhancement and mobility management in 6G NTN. Finally, the challenges in 6G NTN are also illustrated in the aspects on the smooth evolution of the network, the interaction between TN and NTN, and multi-orbit cooperation. The evolution of 6G NTN aims at dealing with these challenges in forthcoming standardization and industry constellation construction.