Main features of 5G New Radio for Non-Terrestrial Networks

As the non-terrestrial networks can provide a wide range of service coverage and the vulnerability of the spaceborne or airborne platform is reduced, interest in providing 5G service using the non-terrestrial networks has been increasing. To benefit from the economies of scale of the 5G ecosystem, interest in integration of the non-terrestrial networks (NTN) into the terrestrial networks has been growing. Integration with the existing terrestrial networks can also provide global connectivity and communications resiliency. Standardization efforts to integrate NTN into the 3rd generation partnership project (3GPP) ecosystem have been ongoing. In this paper, we provide an overview of the state of the art in the non-terrestrial networks working on the 3GPP. Furthermore, we analyze technical challenges, solutions and remaining issues dealing in 3GPP NTN regarding to two main characteristics of the long propagation delay and fast movement of NTN platforms. Finally, our views on 6G standardization towards realization of three-dimensional spatial networks are presented.