# Hierarchical Resource Management for Mega-LEO Satellite Constellation
## 6 Approaches and Algorithms
### Beam Scheduling for Beam-Hopping
In the MLSCS, the size and shape of each cell are also associated with the grids that are used to organize the system. Grids are a set of imaginary lines or boundaries that divide the area covered by the satellite into smaller, more manageable sections. The size and shape of each cell are determined by the arrangement and spacing of these grids. By carefully designing the shape, size, and pointing of satellite beams, as well as the arrangement of grids, satellite communication systems can optimize coverage and communication efficiency. This is particularly important in the MLSCS. * The available resources of SBSs. When determining the amount of bandwidth or data rate that SBSs can provide to each cell in a wireless communication network, it is important to consider not only the total available spectrum but also the spectrum usage policy in the area where the cell is located and the spectrum that is already occupied. * The inter-beam interference. In the beam-hopping satellite communication system, the CCI among beams is a strong constraint. The position relationship between the SBS and the cell determines the azimuth and pitch of the beam pointing, and then the angle between any two beams can be derived from this, which can be used to measure the intensity of the CCI. * The constraints of user fairness and other factors. Fairness is an important consideration in slot allocation among cells in a communication system. It refers to whether the allocation of slots is fair, ensuring that no cell is allocated too many slots while others are allocated too few. When slots are allocated unfairly, some cells may receive too many resources, while others may receive only a few resources or even none at all. This can lead to inefficiencies and unfairness in the system, as users in cells with fewer slots may not be able to access the resources they need to communicate effectively. Given the problems and factors discussed above, SBSs should follow the following guiding principles when scheduling their beams:  
* The cells should be within the service area. The scheduling of resources depends on whether the cells are located within the service area of the SBS. * No CCI between any two beams. To avoid excessive CCI, the angle between any two working beams must comply with the interference threshold. Generally, a larger angle between beams results in lower levels of CCI. * The fairness of slot allocation for all cells. When allocating slots, it is crucial to ensure that the ratio of allocated slots for each cell is proportional to its user demand or service load. However, it is equally important to avoid prioritizing cells with high service loads while neglecting those with lower loads. Ensuring that all cells receive an adequate level of service is necessary for overall network performance. In addition, when designing and calculating beam-hopping patterns, three main spectrum usage schemes are considered. These schemes play a crucial role in optimizing network performance and resource allocation. * Full scheme. All beams use the full frequency band available to the SBS, so they must be separated by a certain angle to avoid and reduce inter-beam interference. * Reuse scheme. The available spectrum of the SBS is divided into multiple non-overlapping sub-bands. To avoid interference between adjacent cells, frequency multiplexing is used, which is similar to multicolor multiplexing. This allows different sub-bands to be used simultaneously among adjacent cells without causing interference. * Hybrid scheme. Some beams use the full frequency band, while others use only a partial frequency band. During beam scheduling, cells with overlapping frequency bands need to calculate the angle between their beams. If interference is detected, the beams cannot illuminate the cells at the same time slot. The beam scheduling algorithm includes several sub-algorithms. The first is the azimuth and pitch calculation algorithm, which is used for beam pointing.