Joint Trajectory and Power Optimization for Jamming-Aided NOMA-UAV Secure Networks

The combination of nonorthogonal multiple access (NOMA) technique and unmanned aerial vehicle (UAV) provides an effective solution for achieving massive connections and improving spectrum efficiency. However, the related security risk becomes serious due to the line-of-sight (LoS) channels involved and high transmit power for weaker users in NOMA-UAV networks. In this article, a UAV-assisted NOMA transmission scheme is proposed to achieve secure downlink transmission via artificial jamming, where a UAV flies straightly to serve multiple ground users in the presence of a passive eavesdropper. During the flight, only the closest NOMA users are chosen to connect with the UAV in each time slot to achieve high LoS probability. To balance the security and transmission performance, the tradeoff between the jamming power and the sum rate is investigated by jointly optimizing the power allocation, the user scheduling and the UAV trajectory. The formulated problem is mixed-integer and nonconvex due to the coupled variables. To address this, we first decompose the problem into two subproblems of power allocation and trajectory optimization. Then, they are transformed into convex ones via the first-order Taylor expansion. After that, an iterative algorithm is proposed to solve the convex problem. Finally, numerical results show that the security of the network is well enhanced and verify the effectiveness of the proposed scheme.