Secure Beamforming and Artificial Noise Algorithms in Cognitive Satellite-Terrestrial Networks With Multiple Eavesdroppers

In this paper, we study the secure beamforming (BF) and artificial noise (AN) techniques for a cognitive satellite-terrestrial network, where a satellite system termed as the primary network under the interception of multiple unauthorized eavesdroppers shares the spectrum of resources with multi-cell secondary terrestrial networks. The design objective is to minimize the total transmit power on board the satellite and multiple terrestrial base stations (BSs) while meeting the secrecy rate constraint of the primary satellite user along with the signal-to-interference-plus-noise ratio constraints of secondary terrestrial users. When exact channel state information at the satellite and terrestrial BS is perfectly known, a zero-forcing scheme is first presented to obtain a sub-optimal solution with low complexity. Next, we propose a semi-definite relaxation-based iterative algorithm together with a golden section search method to achieve the optimal solution. Moreover, a joint BF and AN scheme is further explored to provide the additional degree-of-freedom against illegitimate eavesdropping. Eventually, numerical simulations are given to confirm the validity of the proposed schemes as well as the performance improvements compared with the existing approaches.