# Beam-Hopping-Based Resource Allocation in Integrated Satellite-Terrestrial Networks
## 1 Introduction
BH mechanisms in [20; 21; 22; 23; 24; 25; 26; 27; 28] dynamically selected illuminated cells and allocated transmission resources according to traffic demands, aiming to maximize system capacity, guarantee user fairness, or improve energy efficiency. However, the spectrum sharing between satellite and terrestrial systems has not been considered in these works. A BH-based resource allocation scheme for cognitive satellite communication system was proposed in [14], where the frequency band used by each beam depended on the spectrum sensing results from the terminals. In the cognitive satellite-terrestrial network in [15], the BH-based primary satellite system optimized the BH pattern and beam power to improve the weighted capacity-request ratio, while the secondary terrestrial system applied the spectrum detection mechanism to sense the satellite system. Nevertheless, the integrated resource allocation for spectrum sharing between BH-based satellite systems and terrestrial systems has not been investigated, and the approaches in the prior work cannot be directly applied to jointly optimize the performance of both the satellite and terrestrial systems. In this paper, we investigate resource allocation for the ISTN, which consists of a BH-based satellite system and multiple terrestrial systems. It is assumed that the satellite system and the terrestrial systems share the same frequency band, while all spot beams of the satellite also reuse the full bandwidth to further improve the spectrum efficiency. The centralized network control center (NCC) in the ISTN is responsible for resource allocation and management to enhance system capacity as well as satisfy traffic demands of all the satellite and terrestrial systems. The main contributions of this work are summarized as follows:  
* A BH-based spectrum sharing scheme for the ISTN is presented, which constructs the dynamical protection zones according to the beam allocation pattern of the satellite. Compared with the conventional static EZ, the dynamical protection zones can improve the reusability of the frequency resources while avoiding the CCI between the satellite and terrestrial systems. * Based on the spectrum sharing scheme, resource allocation problems are formulated to maximize the weighted sum of capacity of the ISTN and guarantee fairness among the systems, respectively. To obtain optimal solutions, these two optimization problems are reformulated as mixed integer linear programming (MILP) problems based on beam allocation patterns. * To accelerate the resource allocation process, two greedy suboptimal algorithms are proposed to solve problems with low complexity, which are more suitable for real-time resource scheduling in the ISTN. * Simulations are carried out to evaluate the performance of the proposed algorithms. The simulation results show that the proposed resource allocation algorithms achieve higher spectrum efficiency and better matching between transmission capacity and traffic demands of both the satellite and terrestrial systems. It is also shown that both greedy algorithms with low complexity can achieve performance close to that of the optimal algorithms. The rest of this paper is organized as follows. Section 2 describes the scenario and the spectrum sharing scheme of the ISTN. The downlink transmission models for the satellite and terrestrial systems are also provided in this section. Resource allocation problems in the ISTN are formulated in Section 3. Optimal and greedy suboptimal algorithms for the two resource allocation problems are proposed in Section 4 and Section 5, respectively. Section 6 presents the simulation results, and Section 7 concludes this paper.