Energy-efficient physical layer security schemes for low Earth orbit satellite systems

This paper introduces four proposals to enhance physical layer security (PLS) in low Earth orbit (LEO) satellite systems. The first proposal leverages the Alamouti code aided by artificial noise (AN) and involves the collaborative use of two LEO satellites, ensuring secure downlink transmission. Its efficiency is further enhanced when implementing a power-balanced Alamouti code. The second PLS proposal capitalizes on an reconfigurable intelligent surface (RIS) to introduce interference to potential eavesdroppers. As the RIS manages the reflected channel, this security measure is achieved without necessitating additional transmit power or receiver operations. The third proposal integrates the first and second solutions, resulting in improved secrecy rates compared to the individual proposals, nearly reaching the maximum achievable rate. The fourth proposal is based on a relay-based method, securing all transmission links from the satellite to the relay and from the satellite and relay to the legitimate user. The secrecy performance simulation results presented in the paper demonstrate the remarkable effectiveness of the proposed solutions.