In this paper, we consider a cooperative communication network where multiple low-Earth-orbit (LEO) satellites provide services to multiple ground users (GUs) cooperatively at the same time and on the same frequency. The multi-satellite cooperation has great potential in extending communication coverage and increasing spectral efficiency. Considering that the on-board radio-frequency circuit resources and computation resources on each satellite are restricted, we aim to propose a low-complexity yet efficient multi-satellite cooperative transmission framework. Specifically, we first propose a hybrid beamforming method consisting of analog beamforming for beam alignment and digital beamforming for interference mitigation. Then, to establish appropriate connections between the satellites and GUs, we propose a heuristic user scheduling algorithm which determines the connections according to the total spectral efficiency increment of the multi-satellite cooperative network. Next, considering the intrinsic connection between beamforming and user scheduling, a joint hybrid beamforming and user scheduling (JHU) scheme is proposed to dramatically improve the performance of the multi-satellite cooperative network. In addition to the single-connection scenario, we also consider the multi-connection case using the JHU scheme. Extensive simulations conducted over different LEO satellite constellations and across various GU locations demonstrate the superiority of the proposed schemes in both overall and per-user spectral efficiencies.

翻译：本文研究了一种协作通信网络，其中多颗低地球轨道（LEO）卫星在同一时间和同一频率上协同为多个地面用户（GU）提供服务。多卫星协作在扩展通信覆盖范围和提升频谱效率方面具有巨大潜力。考虑到每颗卫星上搭载的射频电路资源与计算资源有限，本文旨在提出一种低复杂度且高效的多卫星协作传输框架。具体而言，我们首先提出一种混合波束赋形方法，包括用于波束对准的模拟波束赋形和用于干扰抑制的数字波束赋形。随后，为建立卫星与地面用户之间的适当连接，我们提出一种启发式用户调度算法，该算法根据多卫星协作网络的总频谱效率增量确定连接方式。进一步地，考虑到波束赋形与用户调度之间的内在关联，本文提出一种联合混合波束赋形与用户调度（JHU）方案，以显著提升多卫星协作网络的性能。除单连接场景外，我们还分析了采用JHU方案的多连接情况。针对不同LEO卫星星座及多种地面用户位置的大量仿真结果表明，所提方案在整体频谱效率和每用户频谱效率方面均具有优越性。