Joint user association, resource allocation and trajectory design for multi-UAV-aided NOMA wireless communication systems

In this paper, we investigate a multi-UAV aided NOMA communication system, where multiple UAV-mounted aerial base stations are employed to serve ground users in the downlink NOMA communication, and each UAV serves its associated users on its own bandwidth. We aim at maximizing the overall common throughput in a finite time period. Such a problem is a typical mixed integer nonlinear problem, which involves both continuous-variable and combinatorial optimizations. To efficiently solve this problem, we propose a two-layer algorithm, which separately tackles continuous-variable and combinatorial optimization. Specifically, in the inner layer given one user association scheme, subproblems of bandwidth allocation, power allocation and trajectory design are solved based on alternating optimization. In the outer layer, a small number of candidate user association schemes are generated from an initial scheme and the best solution can be determined by comparing all the candidate schemes. In particular, a clustering algorithm based on K-means is applied to produce all candidate user association schemes, the successive convex optimization technique is adopted in the power allocation subproblem and a logistic function approximation approach is employed in the trajectory design subproblem. Simulation results show that the proposed NOMA scheme outperforms three baseline schemes in downlink common throughput, including one solution proposed in an existing literature.