## 2 Related Works
### Interference Coordination Strategies in Heterogeneous Networks  
Currently, most satellites launched into space are LEO satellites, followed by GEO satellites. As the number of satellites grows rapidly, the integration of LEO and GEO satellite systems is becoming an inevitable trend. However, spectrum sharing between LEO and GEO can lead to co-channel interference, causing communication anomalies. To assess the level of interference from Non-Geostationary Orbit (NGEO) satellite constellations on GEO constellations, Equivalent Power Flux Density (EPFD) is widely used. Many studies use EPFD as the interference threshold for LEO satellites on GEO satellites, and when this threshold is exceeded, appropriate remedial measures need to be taken. The studies [24; 25] examine the scenarios of GEO-LEO coexistence systems in both uplink and downlink interference environments. The research indicates that when both satellite systems use the same frequency band for communication, co-channel interference occurs in both uplink and downlink. To tackle interference issues between GEO and LEO satellites, the International Telecommunication Union Radiocommunication Sector (ITU-R S)1419 introduces several interference suppression techniques for co-channel LEO and GEO systems, such as power control, the use of high-gain antennas, setting up protection zones for ground stations, satellite resource scheduling, link balancing, and geographic isolation [26]. ITU-R S.1430 explains how NGEO satellite ground stations can set up protection zones [27]. ITU-R S.1655 discusses interference suppression schemes for frequency sharing between GEO and NGEO systems in the 37.5-42.5 GHz and 47.2-50.2 GHz bands, including satellite resource scheduling and setting up isolation zones [9]. In satellite communications, to prevent interference from LEO satellites to GEO satellite ground users, an \"Exclusion Zone\" (EZ) is often set on LEO satellites, forcing them to shut off their beams in those areas. The study [28] proposes a static spectrum-sharing method that achieves spectrum sharing between LEO and GEO satellites by limiting communication between LEO ground stations and LEO satellites. In the LEO-GEO coexistence scenario in [25], the authors implement an exclusive angle strategy, setting isolation angles to reduce co-linear downlink interference from LEO satellites to GEO satellite users. The study based on EPFD analysis [29; 30; 31] determines the range of angular separation LEO satellites need to adopt to take avoidance measures. Although these schemes can ensure that the GEO satellite systems are kept within interference limits, they impose certain constraints on the communication of LEO satellite ground mobile terminals. Ensuring service quality of GEO satellite networks by controlling the beam switching of all LEO satellites is challenging in practical applications. Power control is a commonly used method to suppress interference. It manages the interference intensity received by controlling the power output of the interfering transmitter. In the study [32], a beam power control scheme for GEO and LEO satellite coexistence systems is proposed. This scheme aims to maximize the throughput of LEO satellite users under the constraint of GEO satellite users' service quality. However, before executing the algorithm, the scheme does not plan the frequency of LEO satellites, which may lead to overlaps of multiple co-channel beams, thus reducing the communication capacity of LEO satellites. The study [33] proposes a method for spectrum sharing between LEO and GEO satellites achieved through cooperation among LEO satellites. This method utilizes multi-layer LEO constellations, allowing a user to be served by up to four LEO satellites simultaneously. However, it introduces co-channel beam interference among different LEO satellites, increasing the complexity of interference analysis and leading to resource waste, therefore driving up costs.