Analysis of Secure RIS-Aided Hybrid Satellite–Terrestrial Maritime Communication System With CFO, Phase Noise, and Imperfect CSI

In this paper, the exact analytical signal-to-interference-plus-noise ratio (SINR) expressions, for the combined effects of phase noise (PHN) and carrier frequency offset (CFO), are derived for the desired user ship and eavesdropper in the novel Reconfigurable intelligent surface (RIS) aided hybrid satellite-terrestrial maritime (R-HSTM) communication system. For analysis, Walsh Hadamard (WH)-Spread Orthogonal Frequency Division Multiplexing (SOFDM) transmission scheme is employed at Low earth orbit (LEO) satellite and on-shore terrestrial base station sources to support variable bit rate (VBR) transmission at the physical (PHY) layer. These sources are equipped with multiple antennas to perform Maximal ratio transmit (MRT) beamforming towards the passive (P)-RIS. In addition, the system employs artificial noise (AN) injection at sources to further thwart eavesdropping attempts. To sum up, this paper provides a three-layer security at the PHY layer of R-HSTM communication system by employing WH-SOFDM, RIS and AN. For simulation, three-state Fontan satellite/terrestrial maritime channel models forL−band communication are considered. Based on derived SINR expressions, bit error rate (BER) has been evaluated for desired user ship and eavesdropper. Also, secrecy capacity of the proposed system has been analyzed. These performance metrics are investigated considering both perfect and imperfect channel state information (CSI) conditions. In addition, pilot-based channel estimation is performed at the receiver, and closed-form estimation error variance is evaluated for each cascaded channel link. The results illustrate a continuous deterioration in these performance metrics with increase in doppler frequency shift, PHN and channel estimation error variance. Also, average BER performance and secrecy capacity deterioration by 2.5% and 8.33% respectively is illustrated for every increase in estimation error variance by the factor of 0.2. The simulation and analytical results depict a close match. Later, stage-by-stage system computational complexity is assessed for the proposed hybrid system, in comparison to the conventional OFDM based R-HSTM communication system.