Enhancing Remote UAV Swarms Communication via Coordinated Satellites and UAAC-Mounted RIS
The space-air-ground-sea integrated networks (SAGSIN) are anticipated to provide seamless and ubiquitous connectivity in remote areas with deficient infrastructure. Nevertheless, the downlink communication to remote unmanned aerial vehicle (UAV) swarms remains challenged due to ultralong-distance propagation, high mobility, and the deficiency of infrastructure. To address these challenges, this paper introduces a multi-satellite cooperative downlink system assisted by a reconfigurable intelligent surface (RIS), strategically mounted on an unmanned aerial aircraft carrier (UAAC). Through this innovative configuration, the signal propagation environment between satellites and UAV swarms can be intelligently reconfigured. Integrating multi-satellite cooperative diversity and RISreconfigured propagation, the system optimizes the communication performance within the constraints of satellite power. A joint optimization problem aimed at maximizing the total downlink sum rate is formulated, through the cooperative design of satellite beamforming vectors and RIS phase shifts. To efficiently solve this non-convex problem, an alternating optimization (AO)-based algorithm is developed, which alternately applies the weighted minimum mean square error (WMMSE) algorithm for beamforming and manifold optimization (MO) method for phase shift design. Comprehensive simulations indicate substantial performance enhancements over baselines.