Covert Non-Orthogonal Multiple Access

Abstract

We consider hiding a covert (private) message in non-orthogonal multiple access (NOMA) systems by superimposing (embedding) it under non-covert (public) messages. We determine the total detection error probability (sum of false alarm and missed detection probability), the adversary's optimum detection strategy that minimizes the total detection error probability, and the communicator's optimum message hiding strategy that maximizes the total detection error probability. Additionally, we explore exploiting the channel variations to further increase the total detection error probability. We show that the total detection error probability increases and converges to 1 as the number of users increases and that the total detection error probability can be increased by increasing the transmission power when the channel variation is exploited.