Performance analysis for multi-RIS UAV NOMA mmWave communication systems.

In this paper, an unmanned aerial vehicle (UAV) nonorthogonal multiple access (NOMA) system operating in millimeter-wave (mmWave) communications under the aid of multiple reconfigurable intelligent surfaces (RISs) is determined. Specifically, two NOMA users receive messages from UAV via both UAV-RISs-user and UAV-user links using mmWave communications. The closed-form expressions of outage probabilities (OPs) and achievable data rates (ADRs) are successfully derived over Nakagami-m fading channels to investigate the performance of the RISs aided UAV-NOMA-mmWave system. Computer simulations are provided to validate the derived expressions. Numerical results observe that by utilizing RISs, the OPs and ADRs performance of UAV-NOMA-mmWave system is significantly improved in comparison with the case without RISs. More specifically, even with high altitude of UAV (300 m) and high carrier frequency (50 GHz), the OPs of UAV-NOMA-mmWave system with RISs are remarkably lower than those without RISs. Meanwhile, the ADRs with RISs are only higher than those without RISs in low transmit power of UAV. In high transmit power of UAV, ADRs with and without RISs are similar due to the NOMA characteristics. Besides the distances and carrier frequency, the effects of other parameters such as the position of RISs, the number of reflecting elements (REs), and the altitude of UAVs are clarified to obtain the system behaviors. [ABSTRACT FROM AUTHOR]