Artificial Noise Enhanced Short-Packet Covert Communications for UAV Networks

‍ ‍This work we consider an artificial noise （AN） enhanced unmanned aerial vehicle （UAV） covert communications， where the UAV working in full-duplex mode not only receives covert information transmitted by Alice， but also generates AN to degrade Willie’s detection. We formulate an optimization problem of the UAV’s three-dimensional （3D） placement and UAV’s AN transmit power together with Alice’s transmit power. The formulated optimization problem is non-convex and the involved optimization variables are coupled each other closely， which makes it difficult to solve the optimization problem directly. To overcome this difficulty， we first equivalently transform it into a more tractable form according to the implicit characteristics of the optimization problem. Then， we derive analytical expressions for Alice’s transmit power and UAV’s AN transmit power. We next prove that the UAV’s optimal horizontal location must lie on the straight line connecting the Alice and Willie， based on which we derive the UAV’s optimal 3D location. Our simulation results show that the proposed AN scheme can obtain a significant covert transmission performance gain compared with the scheme without AN.