High Altitude Platform Beam Switching and Time Slot Allocation in High-Speed Railway Communications

High altitude platforms (HAPs) are considered promising candidates for providing high-capacity wireless communications. In high-speed railway (HSR) communications, the fast velocity requires frequent handovers and beam switching, incurring expensive costs. In contrast, HAPs are being considered due to their extensive coverage and line-of-sight (LoS) paths. These platforms aim to offer communication capabilities that leverage the advantages of both terrestrial and satellite systems. Due to their extensive coverage, there is no need for frequent beam switching, thereby reducing the requirement for additional overhead costs. However, there can be unexpected floating of HAPs, lead to beam misalignment and deterioration in antenna gain, especially in narrow beams. To address these challenges, we propose an adaptive time slot allocation algorithm with neighbor-grid-based beam search scheme which optimizes the 3D beam direction to maximize the total transmitted data. Simulations show that our scheme achieves near-optimal performance but with lower complexity.