RIS-Aided Space–Terrestrial Secure Communication Under Multieavesdropper and Malignant Interference

In light of the growing necessity for secure satellite communications, harmful interference in channel transmission needs to be considered. By introducing reconfigurable intelligent surfaces (RIS) into the wireless communication system, this article presents a satellite-to-ground transmission system to mitigate harmful interference caused by autonomous aerial vehicles (AAV). We focus on downlink transmissions from satellites to users, examining both single-user and multiuser scenarios in the presence of multiple eavesdroppers. This article aims to maximize the achievable secrecy rate while adhering to the power constraints of the RIS and satellite transmitter, a nonconvex problem. To solve this problem, this article employs several methods to the traditional alternating optimization algorithm to get an integrated advanced techniques method, which includes the LogSumExp function, genetic algorithms, Lagrange multipliers, derivation, and the branch-and-bound method and Karush–Kuhn–Tucker conditions. The proposed framework encompasses ideal active and passive RIS configurations for single-user scenarios and practical continuously adjustable phase RIS and discrete phase RIS for multiuser scenarios. The efficacy of the proposed approach is validated through comprehensive simulations, which demonstrate significant performance improvements over baseline scenarios that lack RIS or employ random phase methods.