  This letter focuses on the physical layer security over two-user
multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA)
networks. A linear precoding technique is designed to ensure the
confidentiality of the message of each user from its counterpart. This
technique first splits the base station power between the two users and, based
on that, decomposes the secure MIMO-NOMA channel into two MIMO wiretap
channels, and designs the transmit covariance matrix for each channel
separately. The proposed method substantially enlarges the secrecy rate
compared to existing linear precoding methods and strikes a balance between
performance and computation cost. Simulation results verify the effectiveness
of the proposed method.
