Robust secure UAV relay-assisted cognitive communications with resource allocation and cooperative jamming

This paper considers a novel scenario, where a physical layer security issue is studied in unmanned aerial vehicles (UAVs)-assisted cognitive relay system. A secondary unmanned aerial vehicle (SUAV) relay delivers information from multiple secondary Internet of things (IoT) devices to a secondary user (SU) under the spectrum sharing with primary users (PUs). In the processing of the information transmission of the SUAV relay, a secondary eavesdropper (SE) wiretaps the information transmitted by the UAV relay with imperfect location information. In order to confuse the SE, a friendly SUAV jammer is employed to transmit jamming signals to the SE. To prevent the SE wiretapping information as much as possible, we aim to maximize average worst-case secrecy rate of the secondary relay network by jointly optimizing robust trajectories and power of the SUAV relay and jammer under the power, trajectories, information causality and multiple interference temperature (IT) threshold constraints. Thus, we formulate the original problem which is a challenging non-convex problem. We propose an effective algorithm to solve the original problem and attain locally optimal solution based on the successive convex approximation (SCA) technology and the alternate optimization method. Simulations are offered to demonstrate that our proposed resource allocation scheme can effectively improve the security performance of the SUAV relay network in comparison with other benchmark schemes.