Abstract This paper proposes a hybrid satellite–terrestrial relay network that integrates advanced technologies, such as physical layer security, fountain coding, non‐orthogonal multiple access, reconfigurable intelligent surfaces (RISs), and partial relay selection (PRS). The satellite transmits fountain‐coded packets to terrestrial relays, where the best relay selected using the PRS algorithm employs the decode‐and‐forward technique to deliver data to two user clusters with RIS support. This setup enhances both reliability and security. Meanwhile, eavesdroppers attempt to intercept the RIS‐reflected signals. Exact closed‐form expressions are derived for the outage probability (OP) and system OP of legitimate users, as well as the intercept probability (IP) and system IP of eavesdroppers. Monte Carlo simulations confirmed the analytical results and examined the effects of the key parameters. Additionally, two benchmark models were developed to facilitate performance and security comparisons with the proposed scheme.
Toan et al. (2026) studied this question.