  The emerging Non-Terrestrial Networks (NTNs) can aid to provide 5G and beyond
services everywhere and anytime. However, the vast emergence of NTN systems
will introduce an unseen interference to both the existing satellite systems
and Terrestrial Networks (TNs). For that, there is a need for novel ideas on
how to efficiently utilize the co-existing systems with the ever-increasing
competition on scarce spectrum resources. Dynamic Spectrum Sharing (DSS) is a
promising technique in which different systems can operate on the same
spectrum, thus increasing the spectrum efficiency and offering better coverage
for the users. In this paper, we present a centralized scheme for achieving
coordinated DSS to protect the primary TN while providing NTN with sufficient
resources. The scheme is evaluated by system simulations in a scenario with a
TN and low earth orbit satellite. The results reveal that in a low traffic
demand situation, the primary TN users are not affected negatively while the
NTN can provide service to the rural area. In high-demand traffic situations,
the peak performance of the TN inevitably suffers but the TN cell edge and NTN
users' performance is improved.
