  The explosive growth of bandwidth hungry Internet applications has led to the
rapid development of new generation mobile network technologies that are
expected to provide broadband access to the Internet in a pervasive manner. For
example, 6G networks are capable of providing high-speed network access by
exploiting higher frequency spectrum; high-throughout satellite communication
services are also adopted to achieve pervasive coverage in remote and isolated
areas. In order to enable seamless access, Integrated Satellite-Terrestrial
Communication Networks (ISTCN) has emerged as an important research area. ISTCN
aims to provide high speed and pervasive network services by integrating
broadband terrestrial mobile networks with satellite communication networks. As
terrestrial mobile networks began to use higher frequency spectrum (between
3GHz to 40GHz) which overlaps with that of satellite communication (4GHz to
8GHz for C band and 26GHz to 40GHz for Ka band), there are opportunities and
challenges. On one hand, satellite terminals can potentially access terrestrial
networks in an integrated manner; on the other hand, there will be more
congestion and interference in this spectrum, hence more efficient spectrum
management techniques are required. In this paper, we propose a new technique
to improve spectrum sharing performance by introducing Non-orthogonal Frequency
Division Multiplexing (NOMA) and Cognitive Radio (CR) in the spectrum sharing
of ISTCN. In essence, NOMA technology improves spectrum efficiency by allowing
different users to transmit on the same carrier and distinguishing users by
user power levels while CR technology improves spectrum efficiency through
dynamic spectrum sharing. Furthermore, some open researches and challenges in
ISTCN will be discussed.
