Secure Communications in Hybrid Cooperative Satellite-Terrestrial Networks

In this paper, we study satellite secure communications with physical layer security techniques in the presence of multiple eavesdroppers. In order to increase the secrecy rate to the legitimate user, a terrestrial base station operates as a two-stage amplify-and-forward (AF) relay to assist the secure transmission. In the first stage, the legitimate user sends artificially generated noise to the satellite using paired carrier multiple access (PCMA) such that the artificial noise only degrades the eavesdroppers' channels. In the second stage, the base station forwards its received satellite signal to the legitimate user via beamforming. In this two-stage transmission, we consider two scenarios with non- colluding eavesdroppers and colluding eavesdroppers. We design beamforming schemes for both the two scenarios and compare the proposed beamforming schemes with the null-space beamforming scheme, which nulls out the signal leakages at all eavesdroppers. Simulation results demonstrate the proposed beamforming scheme performs better than the null-space beamforming scheme. It is also shown that the proposed terrestrial network aided satellite communication has a significant performance improvement of secure performance as compared to direct transmissions.