Physical-Layer Authentication in Non-Orthogonal Multiple Access Systems

This paper concerns the problem of authenticating the transmitter device in non-orthogonal multiple access (NOMA) systems. This problem is important because of high vulnerabilities in wireless communications and an additional security vulnerability when some users collude with the adversary. In this paper, we consider two attacking scenarios. In the first scenario, there is no user that colludes with the adversary. In the second scenario, at least one user colludes with the adversary. In this paper, we propose an authentication approach in the down-link scheme of a NOMA system using physical-layer authentication mechanism because of its advantages: provide information theoretic security, reduce complexity, save power and allow us to construct a two-factor authentication system. Based on the aforementioned two attacking scenarios, we propose three physical-layer authentication schemes for a NOMA system: Physical-Layer Authentication with Shared Authentication Tag (PLA-SAT), Physical-Layer Authentication with Superimposed Independent authentication Tags (PLA-SIT), and Physical-Layer Authentication with TDM authentication tags (PLA-TDM). We analyze the theoretical performance of our schemes over fading channels and derive their closed-form expressions. Then, we optimize the parameters of our schemes to achieve both the reliability fairness and the authentication-accuracy fairness. We implemented our schemes and conducted extensive performance comparisons. Our experimental results show that for the first attacking scenario, the PLA-SAT scheme offers more than 97% authentication accuracy when the received SNR of the served user with poor channel condition is at least 10 dB. For the second attacking scenario, both the PLA-SIT scheme and the PLA-TDM scheme offer more than 97% authentication accuracy when the received SNR of the served user with poor channel condition is at least 12 dB.