UAV-Assisted Covert Transmission for Cooperative Cognitive Radio Networks

Cooperative cognitive radio (CR) networks can enable secondary users (SUs) to access the spectrum without disrupting the transmission of primary users (PUs), which brings a series of security challenges despite the significant increase in spectrum efficiency. In this paper, we propose a novel unmanned aerial vehicle (UAV) assisted covert transmission scheme for cooperative CR networks, where a UAV as the secondary transmitter can send its covert signal to a secondary receiver while ensuring the quality of service for the PU. To achieve the covert transmission of SU, the PU's signal is used as a beneficial interference to disturb the detection of wardens. We first derive the minimum detection error probability and Kullback-Leibler divergence under the finite blocklength constraint. Then, the average effective throughput maximization problem under the probabilistic line-of-sight channel is established by jointly optimizing the UAV's transmit power and trajectory. Finally, numerical results verifies that the UAV relay in the proposed scheme can not only assist in the information transmission of PU but also achieve the covert communication for the secondary network in the presence of multiple wardens.