Analysis and Optimization of UAV-Assisted Covert Communications in Interweave Cognitive Radio Networks

Unmanned aerial vehicles (UAVs) are widely used in communication networks due to the high maneuverability and low cost. Focusing on the problems of limited resources and untrustworthy communication environment, interweave cognitive radio and finite blocklength covert communication techniques are integrated to construct a UAV-assisted transmission scheme in this paper. Firstly, we analyze the considered covert transmission system and extend the chain rule for solving the Kullback-Leibler (KL) divergence. Based on this, a closed-form expression for the KL divergence is obtained, as well as the strict covertness constraints. Further, an optimization problem with the objective of maximizing the effective throughput is presented under the acquired conditions. We obtain the optimal parameter configurations including sensing blocklength, transmission blocklength, transmission power and UAV flight altitude. Additionally, we explore the impact of the random selection of channel use (RSCU) scheme on the performance of the UAV-assisted covert communication in cognitive radio network. Theoretical analyses and simulation results reveal the trade-off between sensing blocklength and transmission blocklength, and the trade-off between false alarm probability and decoding error probability, respectively. Meanwhile, reasonable flight altitude and blocklength allocation can achieve higher effective throughput. Particularly, the RSCU scheme can further improve the performance of the interweave cognitive finite blocklength covert communication system effectively.