Improving Physical-Layer Security for CRNs Using SINR-Based Cooperative Beamforming

In this paper, we consider a new cognitive radio network (CRN), where cooperative beamforming is designed to enhance the physical-layer security for both primary users (PUs) and secondary users (SUs). In particular, the proposed design aims to minimize the transmit power of a secondary transmitter (ST) while providing an eavesdropper (Eve), a primary receiver (PR), and multiple secondary receivers (SRs) with different signal-to-interference-plus-noise ratio (SINR). The semi-definite relaxation (SDR) technique is utilized to convert the initial nonconvex problem into a convex semi-definite programming (SDP), which can be efficiently solved. Then, the optimality of SDR is strictly proved by showing that optimal transmit covariances must be rank one. Numerical examples are provided to corroborate the proposed studies.