Optimizing User Association, Power Control and Beamforming for 6G Multi-IRS Multi-UAV NOMA Communications in Smart Cities

Sixth generation (6G)-enabled smart cities with intelligent reconfigurable surfaces (IRSs), unmanned aerial vehicles (UAVs), and non-orthogonal multiple access (NOMA) technologies have the potential to transform consumer electronics through ultra-fast wireless connectivity, effective resource utilization, and intelligent urban services. This paper presents a new optimization scheme in NOMA multi-UAV (M-UAV) networks by utilizing IRSs. The proposed scheme focuses on ground user equipment (GUE) UAV association, UAV power allocation and IRS passive beamforming (BF), with the objective of enhancing the system's spectral efficiency (SE) under the assumption of imperfect successive interference cancellation (i-SIC). To tackle the non-linearity of the problem, we first perform GUE UAV association for available power allocation and BF. Then, we decouple the joint transmit power and BF design problem into two parts. Subsequently, an efficient solution is achieved by employing a combination of sequential quadratic programming, successive convex approximation, and difference-of-convex programming techniques. Through comprehensive numerical evaluations, we validate the effectiveness of the mathematical solution and demonstrate the superiority of our proposed optimization scheme over benchmark schemes. The results showcase notable performance improvements in terms of SE, thereby highlighting the potential benefits that can be achieved by leveraging the proposed approach in NOMA M-UAV networks.