Multicast Multigroup Beamforming for Frame-Based LEO Satellite Communications

In current work, multibeam satellites often use full-frequency reuse (FFR) to improve throughput, and beamforming is widely used in order to resolve inter-beam interference. In addition, the current mainstream satellite communication (SATCOM) standards require serving multiple users in a single frame, and this transmission strategy is similar to physical layer multicasting. In this paper, we investigate the multicast beamforming problem in low earth orbit (LEO) satellite systems. In the existing grouping approach, satellites can only serve a small number of users at the same time. Therefore, we establish the sum-rate maximisation problem for the system under the constraints of user grouping, power per antenna and minimum rate requirement for multicast groups. To solve this problem, we first complete user grouping based on users channel correlation and beam radius constraints. Then the beamforming design is converted into a difference-of-convex (DC) problem by some operations and an iterative algorithm based on a concave process is used to solve the problem. Finally, the simulation results show that the system sum rate of the FMBF scheme proposed in this paper is improved by 28.6% compared to the JSP scheme.