Secure Beamforming for MIMO-NOMA-Based Cognitive Radio Network

Cognitive radio network (CRN) and non-orthogonal multiple-access (NOMA) play the crucial roles in the fifth generation wireless communication systems. However, the physical-layer security still remains quite challenging. In this letter, a downlink cascaded transmitting zero-forcing-beamforming (ZFBF) technique is proposed to secure communications in a two-cell multiple-input multiple-output (MIMO) NOMA-based CRN. The proposed technique protects the information from illegitimate users (eavesdroppers) within the same and adjacent cells. The restriction on the number of at the transmitter can also be relaxed by applying the signal alignment for the ZFBF technique. This proposed new method can maximize the total secrecy rate of the MIMO-NOMA-based CRNs in the lack of conventional transceiver beamforming techniques. Numerical and simulation evaluations have demonstrated the effectiveness of the proposed method.