Secure transmission in AF satellite system based on FH‐MWFRFT and null space beamforming

Abstract

This study investigates the information security problem in amplify-and-forward (AF) satellite transmission with eavesdroppers at both the transmitter and the receiver. Two multi-antenna earth stations aim to exchange messages through a multi-antenna satellite in two hops. The satellite channels (both uplink and downlink) are assumed to be shadowed-Rician fading. In the first hop, the multiple term weighted fractional Fourier transform (MWFRFT) is adopted to secure the messages from the eavesdropper at the transmitter. To overcome the simplicity of parameters in MWFRFT, the authors enhance the MWFRFT with frequency hopping and propose the frequency hopping multiple term weighted fractional Fourier transform (FH-MWFRFT) to improve the secrecy. In the second hop, the satellite broadcasts the signal to the receiver after null space beamforming (NSBF). Since the energy at the satellite is confined, the NSBF is simplified by applying the singular value decompose to avoid the complicate optimisation calculations at the satellite. The one-way and two-way transmission scenarios with full channel state information (CSI) and statistic CSI are both considered in this study. Simulation results demonstrate the proposed method could achieve a better security at the transmitter while maintain a similar secrecy performance to the optimisation method at the legitimate receiver.