Secrecy Energy Efficiency Maximization for Active RIS-Assisted Satellite Communications Against Cooperative Eavesdroppers and Jammers

Satellite communication has attracted considerable interest for its potential to achieve seamless global connectivity. However, it remains vulnerable to illegal interception and malicious jamming, along with stringent energy efficiency demands. This letter addresses the dual challenges of security and energy efficiency by investigating a satellite downlink system aided by an active reconfigurable intelligent surface (RIS), in which multiple eavesdroppers (Eves) and malicious jammers collaborate to degrade transmission security. We aim to maximize the secrecy energy efficiency (SEE) under constraints on each user’s achievable rate and the power budgets of both the satellite and active RIS. Considering the practical limitation of imperfect channel state information for Eves, a sophisticated two-layer alternating optimization framework is proposed to jointly optimize the satellite’s transmit beamforming matrix and the reflection coefficient matrix of the active RIS. Simulations results confirm the superiority of the proposed scheme in terms of SEE compared to several benchmark methods, demonstrating its effectiveness in achieving robust security with high energy efficiency under imperfect channel conditions.