Energy-Efficient Resource Allocation in Multi-UAV Networks With NOMA

Abstract

This paper investigates the energy efficiency (EE) optimization in a wireless communication network where multiple UAVs serve different types of devices, namely, information receivers (IRs) and energy receivers (ERs). The UAVs transmit power signals towards the ERs, and then enable data transmission to IRs on the downlink and from ERs on the uplink with non-orthogonal multiple access (NOMA). The optimization problem to maximize the overall EE is formulated and solved using Lagrangian optimization and gradient-descent methods. The optimization is decomposed into two sub-problems. Firstly, by connecting the path loss of the devices' channels with their rate demands, the UAVs' optimal positions are obtained. Then, based on the obtained UAVs' optimal positions and a closed-form expression for the EE, a resource allocation aiming to maximize EE is developed. For the simulations, two main scenarios for single and multiple UAVs are considered. Numerical results and comparisons are provided. In particular, for the single-UAV scenario, the results show an enhancement in EE for the operation with NOMA compared with OMA. For the multiple-UAV scenario, several cases depending on different combinations of the devices' rate requirements are considered. The results show the superiority of NOMA over OMA in all use cases. The results also reveal the effect of considering the devices' rate requirements on the EE, where the case with equal rate requirements has the best performance.