# Interference-Aware Radio Resource Management for Cognitive High-Throughput Satellite Systems
## 1 Introduction  
A multi-faceted fifth-generation (5G) system is expected to have the ability of ubiquitous access to high-data-rate services/applications from any device anytime and anywhere, driving the revolution to a highly efficient network architecture. In this context, satellite communications, which are complementary to terrestrial networks, are becoming an inherent part of 5G and beyond 5G eco-systems [1; 2; 3]. As a matter of fact, satellite communications can not only provide coverage for areas without backbone connectivity (e.g., maritime, aeronautic, rural, and emergency), but also deliver high capacity broadband services for high-density population scenarios to decongest existing terrestrial wireless networks. With the ever-increasing demand for high-speed multimedia and broadband services, high-throughput satellite (HTS) systems [4] are emerging as a promising paradigm to provide on-demand coverage and large-capacity communications for maritime networks [5] and Unmanned Aerial Vehicle UAV surveillance [6]. Equipped with an array-fed reflector, the HTS system can produce a large number of beams, enabling interactive broadband services on top of broadcasting. Although a number of Ka-band HTS systems have already been deployed, due to the spectrum shortage, there is still a large gap with respect to the throughput requirement of the next generation of terabit/s satellites within the 2020 horizon [7]. The main reasons and the related solutions are summarized in Table 1.  
One reason for the limited throughput is the inefficient utilization of the deployed spectrum in HTS systems. To increase the bandwidth utilization efficiency, the authors in [8] proposed to dynamically allocate the orthogonal bandwidth based on different traffic demands. For an orthogonal frequency division multiple-access-based satellite forward link, the authors in [9] combined the multicast resource allocation schemes and application-layer joint coding to enhance the performance of mobile satellite systems. In [10; 11], although the authors proposed dynamic frequency allocation schemes to enhance the frequency flexibility, the conventional four-color frequency reuse (4 FR) scheme was still employed to ensure interference isolation at the expense of lower spectrum utilization, which results in a capacity reduction problem. Moreover, the authors in [12] proposed a priority code scheme (PCS) to mitigate the unsuitable allocations of frequency resources in the HTS system, where the frequency-reuse pattern is assumed to be three to provide spatial separation among beams operating on the same frequency. In this way, no interference or little interference is exposed on adjacent beams while the spectrum is underutilized. To boost the achievable spectral efficiency of the broadband high-throughput multibeam satellite systems, a promising approach is to use a more aggressive frequency reuse pattern combined with interference mitigation techniques [13]. In this context, full frequency reuse (FFR) among beams along with multiuser interference detection and cancelation on the user side or an advanced radio resource management (RRM) strategy at the transmitter side is emerging as a promising way towards the efficient utilization of the available spectrum and the increase of the overall system throughput [27]. Specifically, the authors in [14] designed a multiuser detection technique to alleviate the inter-beam interference and investigated the capacity performance of multibeam satellite communication systems using a rain fading model. In [15; 16], precoding-based transmission schemes were designed to enable full frequency reuse in multibeam satellite systems. Another reason for the limited throughput is the exclusive regulation of spectrum assignment. According to ITU-R [17], only a 500 MHz spectrum in the Ka band is exclusively available for HTS, which has been shown to be insufficient to meet the forthcoming demands for broadband satellite services.