Channel Inversion Power Control Aided Covert Communications in Uplink NOMA Systems

In this letter, we investigate covert communications in uplink non-orthogonal multiple access (NOMA) systems, where a covert user tries to transmit private information to a legitimate receiver without being detected by a warden. Specifically, the covert user is shielded by a public user with truncated channel inversion power control, which works as a random transmit power jammer to interfere the warden's detection. To this end, we derive the closed-form expressions of the detection error probability and optimal detection threshold at the warden. Furthermore, we present the optimal choice of the power control parameter to achieve the maximum effective covert throughput (ECT). Our analysis and numerical results indicate that boosting the maximum transmit power of public user both increases the covertness and prior transmission probability, which leads to a larger ECT.