# Hierarchical Resource Management for Mega-LEO Satellite Constellation
## 4 Hierarchical Resource Management Architecture  
To leverage the low loss and delay of LEO satellites while addressing the challenges posed by their high-dynamic characteristics, the system resource scheduling must be real-time, flexible, and efficient. Optimal resource management schemes must be implemented across multiple domains, including time, space, frequency, and energy (or power). These resource scheduling strategies and approaches differ at various levels within the system, including NCC, SBSs and user terminals. Therefore, it is essential to design a hierarchical resource management architecture that aligns with the distribution and scheduling demands of resources at these different levels. By adopting a hierarchical approach, resource management can be more flexible and efficient compared to considering the entire network as a single entity. Further details on the design and implementation of this hierarchical architecture will be provided in subsequent sections. Resource management in satellite communication systems is closely tied to the constellation design and coverage scheme. The large bandwidth of these systems allows for a high frequency reuse factor, which helps to minimize co-channel interference (CCI) in overlapping coverage areas of SBSs. In multi-beam or beam-hopping systems, the spectrum is efficiently multiplexed among beams to improve spectrum efficiency. Spot-beams, which are primarily responsible for data transmission in satellite communication systems, require a significant amount of bandwidth. However, because spot-beams are spatially isolated, a smaller frequency reuse factor can be used among them to enhance spectral efficiency. Furthermore, multi-beam or beam-hopping technology can be employed to increase the spectrum reuse factor and reduce inter-beam CCI, further optimizing resource management in satellite communication systems. Compared to traditional GEO and multi-beam satellite communication systems, resource scheduling in the MLSCS is significantly more complex. The limitations of satellite resources, such as power, bandwidth, and beam, require a careful balance between providing global on-demand service and optimizing resource utilization. Additionally, the dynamic nature of coverage areas in MLSCS necessitates an adaptive resource scheduling approach. Based on the service data flow and resource distribution within the system, wireless resource scheduling in the MLSCS can be divided into three levels. These levels may include high-level strategic scheduling, mid-level tactical scheduling, and low-level operational scheduling, each with its own unique challenges and considerations. * Level 1: To ensure efficient and effective utilization of satellite resources, it is necessary to consider the division of satellite service areas and the available spectrum resource planning. By leveraging these elements, we can guide satellites to carry out multi-satellite service coordination, ensuring that they operate in a complementary and synergistic manner. Furthermore, by establishing a unified global collaborative service system, we can enable seamless communication and data sharing across different satellite networks, promoting a more integrated and efficient satellite communication ecosystem. * Level 2: To ensure optimal utilization of satellite resources, we allocate them to user terminals based on their specific needs and requirements. This allocation process involves guiding user terminals to access SBSs that are strategically located to provide the best possible coverage and service. Once user terminals are connected to SBSs, data interaction between them is realized through a secure and efficient communication protocol. This protocol ensures that data are transmitted and received in a timely and accurate manner, promoting seamless communication and data sharing across the satellite network. * Level 3: This level schedules user data for various service types, such as real-time, best-effort, and guaranteed delivery services.