Satellite communications are envisioned as a key enabler for ubiquitous coverage in future 6G networks, yet the broadcast nature renders them vulnerable to eavesdropping, especially given the long-distance transmissions and associated high uncertainties. In this paper, we propose the physical layer security enhancement for multi-beam satellite communications with the assistance of an aerial reconfigurable intelligent surface (ARIS). Considering the high dynamics and uncertainties of channels, we characterize the channel distribution with moment-based ambiguity sets. Accordingly, a distributionally robust secrecy rate optimization is formulated through joint design of transmit and reflection beamforming. We then introduce a conditional value-at-risk-based reformulation to convert the probabilistic constraints into deterministic forms. An alternating optimization framework is subsequently employed to iteratively update the transmit and reflective beamforming vectors until convergence. Simulation results demonstrate that the proposed distributionally robust scheme significantly enhances secrecy performance, and maintains reliable performance across various channel error distributions.

翻译：卫星通信被视作未来6G网络实现全球覆盖的关键使能技术，然而其广播性质使其易受窃听攻击，特别是在远距离传输和高不确定性场景下更为突出。本文提出一种利用空中可重构智能表面(ARIS)增强多波束卫星通信物理层安全的方法。考虑到信道的高动态性与不确定性，我们基于矩模糊集对信道分布进行建模。在此基础上，通过联合设计发射与反射波束成形，构建了分布式鲁棒保密速率优化问题。进而引入条件风险价值(CVaR)重构成方法，将概率约束转化为确定性形式。随后采用交替优化框架迭代更新发射与反射波束成形矢量直至收敛。仿真结果表明，所提出的分布式鲁棒方案能显著提升保密性能，并在多种信道误差分布下保持稳定可靠性能。