NOMA and IRS-assisted Secure UAV Communications

With the advantages of intelligent reflecting surface (IRS), we consider an IRS-assisted unmanned aerial vehicle (UAV) secure communication system, in which multiple ground users (GUs) are served by the UAV in the presence of a ground eavesdropper. We adopt the non-orthogonal multiple access (NOMA) technique to access GUs. The phase shift matrix of IRS, the trajectory, and transmit power of the UAV are jointly optimized to maximize the GUs' average secrecy rate. However, this problem is highly intractable due to its non-convexity. Therefore, we first divide the formulated problem into three subproblems using the alternating optimization technique. Then, we transform the subproblems into solvable ones by utilizing successive convex approximation and semidefinite relaxation methods. Finally, we develop an effective algorithm to obtain the solution. Simulation results indicate that our scheme can achieve better performance gains compared to the baseline schemes.