A Secure Hybrid Satellite-Terrestrial Communication Network With AF/DF and Relay Selection

This paper makes research on a secure hybrid satellite-terrestrial communication network with eavesdroppers at the primary and secondary receivers. To secure the transmitted messages, we adopt the null space beamforming to the amplified-and-forward (AF) relay protocol and weighted fractional data carrying artificial noise (WFDCAN) to the decoded-and-forward (DF) relay protocol at the satellite. Considering the time delay may be brought by the WFDCAN, we introduce a parameter theta to indicate the delay severity. The secrecy capacity is combined with theta to derive the maximum secrecy delay constrain. The secrecy capacity, the ASER of the up-link channel and the delay constrain of the down-link channel are applied as factors for a three level relay protocol selection scheme. To simplify the analyses and expressions, the models of the AF protocol and the DF protocol are integrated to form a new transmission model. Furthermore, the secrecy performance at the destination receiver is considered for terrestrial relay selection to enhance the security performance. We also apply the columns of the frequency hopping based multi-term weighted fractional fourier transform (FH-MWFRFT) matrix as signal processing vector to the base station of the terrestrial network to minimize the interference it brings to the terrestrial relays. The simulation results demonstrate that the proposed system could maintain the security at the relays and the secondary receiver while reducing the delay at the satellite in some conditions.