Owing to the ever increasing of information privacy requirement, covert communication has gained more and more attention, whose effective range is limited by the trade-off between the covertness and the transmit power. Benefiting from the high mobility and easy deployment, unmanned aerial vehicles (UAVs) can be utilized to expand the range of covert networks. Thus, we propose a UAV-relayed covert communication scheme with finite blocklength to maximize the effective transmission bits from the transmitter to the legitimate receiver against a flying warden. The transmitter adopts the maximum ratio transmission and the relay performs Gaussian signalling transmission to cause uncertainty at the warden. First, the optimal detection thresholds are derived at the warden towards the transmitter and the relay, respectively. Then, the hovering location of the warden is optimized to maximize the summation of relative entropies from the transmitter and the relay, which can greatly threaten the covertness. With this worst covert situation, the blocklength and transmit power at the transmitter and the relay are jointly optimized under the constraint of the end-to-end error detection probability to maximize the effective transmission rate from the transmitter to the legitimate receiver. Numerical results are provided to demonstrate the effectiveness of the proposed UAV-relayed covert communication scheme.

中文翻译：

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无人机中继与飞行典狱长的秘密通信


由于信息隐私要求的不断提高，隐蔽通信越来越受到人们的关注，其有效范围受到隐蔽性和发射功率之间的权衡的限制。受益于高机动性和易于部署，无人机（UAV）可用于扩大隐蔽网络的范围。因此，我们提出了一种具有有限块长度的无人机中继隐蔽通信方案，以最大化从发射器到合法接收器的有效传输比特，以对抗飞行典狱长。发送端采用最大比值传输，中继端进行高斯信令传输，给管理员带来不确定性。首先，在管理员处分别针对发射器和中继器导出最佳检测阈值。然后，对守望者的悬停位置进行优化，以最大化来自发射器和中继器的相对熵的总和，这可以极大地威胁隐蔽性。在这种最糟糕的隐蔽情况下，在端到端错误检测概率的约束下，对发射机和中继处的块长度和发射功率进行联合优化，以最大化从发射机到合法接收机的有效传输速率。提供的数值结果证明了所提出的无人机中继隐蔽通信方案的有效性。