RIS-carried UAV communication: Current research, challenges, and future trends

Enhanced quality of service (QoS) and resource allocation are important measurements in a mobile communication system. Compared to traditional mobile networks, 6G uses spectrum from 0.3 to 3 terahertz (THz) and millimeter wave (mmWave) from 30 to 300 GHz (GHz), making QoS and proper resource allocation difficult. Unmanned aerial vehicles (UAVs) have garnered attention in academia and industry because of their high mobility, elastic placement, cost-efficiency, and easy combination with other communication systems. Similarly, reconfigurable intelligent surfaces (RISs) also gain the attention of the wireless research community owing to their precise signal reflection, spectrum, and energy efficiency, as well as their capability of regulating waveforms such as amplitude, frequency, polarization, and phase using passive reflections. The UAV has several weaknesses and is plagued by eavesdroppers, blockage, etc. Likewise, deploying RIS also is ineffective in standalone scenarios due to the user's mobility. Thus, we comprehensively review recent studies on UAV and RIS technologies. Furthermore, we have discussed the challenges of future communication technologies evolving RIS-assisted UAVs and future trends. We aim to provide sufficient information for the research on UAV and RIS's revolutionized phases, problems, and research trends.(c) 2023 The Authors. Published by Elsevier B.V. on behalf of The Korean Institute of Communications and Information Sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).