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Delay-Intolerant Covert Communications With Downlink Non-orthogonal Multiple Access

In this paper, we investigate the delay-intolerant covert communications with non-orthogonal multiple access (NO-MA), where a fixed effective covert throughput (ECT) at the NOMA-weaker user is guaranteed for the consideration of user fairness. Specifically, we derive a lower bound of the total detection error probability at the warden. Furthermore, we optimize the total transmit power and power allocation factor to maximize the ECT at the NOMA-strong user. Our analyses show that delay-intolerant covert communication can be achieved in the NOMA system, where the maximum ECT is achieved when all the channel uses are utilized. Comparing the covert performance between NOMA and OMA, we find that NOMA has no superior covert performance over OMA in delay-intolerant covert communications.