Performance optimization of active RIS-assisted UAV communications

Abstract

Unmanned aerial vehicles (UAVs) are considered a promising technology for the future sixth-generation (6G) systems because of their advantages, such as extended coverage, energy efficiency, concentrated signal, adaptability, and capacity to offer ground terminal computing services. Utilizing UAVs can greatly minimize compute task latency and improve system performance. Furthermore, Reconfigurable Intelligent Surfaces (RISs) are an emerging technology that has the potential to improve wireless networks’ propagation environments. UAV-assisted RIS communications are considered a potential solution for future generations of networks. We consider a downlink communication scenario where an UAV operating as a base station is assisted by an active RIS. By simultaneously adjusting the UAV beamforming and RIS coefficients, we hope to maximize the sum rate of users. We propose an iterative algorithm for solving this problem. Then, we analyse the system performance in terms of total rate, energy efficiency, and robustness to channel estimate errors, while explicitly accounting for the power consumption of active RIS components. A comparison with a standard passive RIS-assisted UAV network is also conducted. Numerical results confirm that the active RIS compensates for the considerable path loss associated with UAV-to-ground channels, hence significantly increasing the sum rate. Additionally, the suggested system provides improved energy efficiency in the low-to-moderate power regime, owing to the superior spectrum efficiency given by signal amplification