Enhancing Physical Layer Security of Cooperative NOMA Systems Using User Selection

AbstractIn this paper, we study a physical layer security improvement method for a multi-user cooperative non-orthogonal multiple access (NOMA) system in the presence of an adaptive eavesdropper. In the system, the eavesdropper adaptively switches the eavesdropping mode and interference mode. In order to resist the eavesdropping attack of the eavesdropper, a number of device-to-device (D2D) relay users are available for cooperating to forward legitimate signals, and one of them can be selected for assistance through a user selection strategy based on the channel side information (CSI) of the eavesdropping channel. The selected relay uses the NOMA technology to superimpose ordinary signals that only require data services with the received sensitive signals, and then forwards the superimposed signals. The ergodic secrecy sum capacity lower bound of the system is derived. Theoretical analysis and Monte Carlo simulation show that the performance of the proposed multi-user cooperative NOMA system is better than that of the single-relay user cooperative system.KeywordsNon-orthogonal multiple accessDevice-to-deviceUser selectionErgodic secrecy sum capacity