Sum Secrecy Rate Maximization in NOMA-Based Cognitive Satellite-Terrestrial Network

In this letter, we present a joint beamforming design for non-orthogonal multiple access (NOMA)-based cognitive satellite-terrestrial network (CSTN), where satellite network applies orthogonal multiple access (OMA) technology and NOMA scheme is utilized by the terrestrial network. The scheme key is to maximize sum secrecy rate of satellite users under the imperfect channel state information, while meeting the rate requirements of terrestrial users and transmit power constraints of the CSTN. Since the formulated optimization problem is non convex and intractable, we convert the original non convex maximization problem to a corresponding tractable convex one by successive convex approximation (SCA) and semidefinite relaxation (SDR), and then propose an SCA-based iterative beamforming algorithm to get the secure beamforming vectors. Finally, numerical simulation results are provided to verify the effectiveness and superiority of the proposed joint beamforming design.