UAV-relay Assisted Covert Communication with Finite Block-length

To avoid the high detection in long-distance covert communications due to the large transmission power, an Unmanned Aerial Vehicle ( UAV)-relay based covert communication scheme with finite block blocklength is proposed in this paper. Firstly, the Signal-to -Noise-Ratio (SNR) at the legal receiver via the UAVrelay is derived, based on which the outage probability and throughput of the covert communication link are also obtained. Secondly, the detection performance of the monitor is analyzed, i.e. KL (Kullback- Leibler) scatter, and it is used as a constraint on the covert communication. Finally, to maximize the throughput of the covert communication, the transmission power at the transmitter and the UAV-relay, as well as the flight height of UAV are jointly optimized. The simulation results verify the performance of the proposed covert communication scheme, and also show its superiority to the traditional strategies without UAVs since it greatly reduces the KL divergence at the warder.