Artificial Noise With Network Coding for Securing NOMA-Assisted Cooperative Networks

We investigate security-reliability tradeoff (SRT) for a non-orthogonal multiple access (NOMA)-aided cooperative network, where an internal untrusted far user (UFU) intercepts transmission from source to trusted near user (TNU), and an external eavesdropper (Eve) overhears transmission from source to UFU and TNU. To prevent eavesdropping, an artificial noise (AN)-aided network coding (ANANC) scheme is presented and exact expressions of outage probabilities (OPs), intercept probabilities (IPs), and transmission secrecy outage probabilities (TSOPs) are derived for NOMA users. For comparison, the simulation results of AN without network coding (ANWNC) scheme and non-AN (NAN) scheme are presented. Numerical results show that: 1) the IPs of TNU by the ANANC scheme is lower than that by the ANWNC and NAN schemes slightly deteriorating OP; 2) UFU by the ANANC, ANWNC, and NAN schemes achieves almost the same OP and NAN scheme performs the worst IP performance; 3) SRT of TNU by the ANANC scheme is superior to ANWNC and NAN schemes without damaging SRT for UFU compared to the ANWNC scheme but being better than that of the NAN scheme; 4) secrecy energy efficiency (SEE) of TNU by the ANANC scheme performs better than that of the ANWNC and NAN schemes but has a negligible impact on UFU in a high transmit power region, while both NOMA users have comparable SEE to ANWNC and NAN schemes in a low transmit power region.