# Interference-Aware Radio Resource Management for Cognitive High-Throughput Satellite Systems
## 1 Introduction
To alleviate the spectrum scarcity in future satellite communications, employing cognitive radio (CR) technology in satellite communications has emerged as a promising candidate, which is referred as a so-called cognitive satellite-terrestrial network [18; 19]. For the cognitive satellite-terrestrial networks, effective resource allocation, which is a key enabling technique to alleviate the mutual interference and ensure the friendly coexistence of two networks, has also \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Problems** & **Reasons** & **Solutions** & **References** \\ \hline \hline \multirow{8}{*}{Limited throughput of HTS systems with underutilized spectrum} & \multirow{4}{*}{Partial frequency reuse pattern [8; 9; 10; 11; 12]} & Full frequency reuse pattern with interference management [13] & [14]: Multiuser interference detection and cancelation on the user side \\ \cline{1-1} \cline{2-4}  & & & [15; 16]: Advanced precoding schemes at the transmitter side \\ \cline{1-1} \cline{2-4}  & & & [20; 21]: Various interference scenarios and cognitive modes in cognitive satellite terrestrial networks \\ \cline{1-1} \cline{2-4}  & & & [22]: Cognitive zone to guarantee the primary communications \\ \cline{1-1} \cline{2-4}  & & & [23]: A joint carrier–power-bandwidth allocation scheme \\ \cline{1-1} \cline{2-4}  & & & [24; 25; 26]: Power allocation with interference-power constraints \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The main reasons and the related solutions for limited throughput of high-throughput satellite (HTS) systems. been widely studied. The authors in [20] presented several basic scenarios and system models for cognitive satellite-terrestrial networks, where satellite and terrestrial networks can operate as primary and secondary systems, respectively, or vice versa. In regard to spectrum sharing, cognitive satellite-terrestrial networks can operate on various modes, e.g., underlay, overlay, and interweave [21]. The underlay mode, in which the cognitive system is allowed to share the spectrum licensed to the primary system without causing excessive interference at the primary user, is especially attractive due to its effective spectrum utilization. In this context, various resource allocation schemes were studied to optimize the performance of cognitive satellite-terrestrial networks. In particular, the authors in [22] designed a cognitive zone to guarantee the primary satellite communication while providing high service availability to secondary terrestrial users. The authors in [23] proposed a joint carrier-power-bandwidth allocation scheme to maximize the throughput of the satellite network, which operates in the microwave frequency band. In [24], the authors introduced a power allocation scheme that can optimize the effective capacity of terrestrial communications for given quality of service (QoS) requirements while guaranteeing the outage probability (OP) of satellite communications. In [25], the authors conducted power allocation to maximize the achievable rate for cognitive hybrid satellite-terrestrial networks with amplify-and-forward (AF) relays. In addition, for real-time satellite applications in cognitive satellite-terrestrial networks, the authors in [26] conducted power control to maximize the delay-limited capacity without degrading the communication quality of the primary terrestrial user. From the above analyses, we can see that there are already some works devoted to improving the spectrum utilization from the perspective of full frequency reuse patterns and cognitive radio, along with effective co-channel interference (CCI) mitigation schemes. However, relying on either of these two technologies alone is not enough to meet the capacity demands of satellite communication systems in 5G and beyond, which motivates the work in this paper. The novelties and contributions of this paper are surmised as follows.