RIS-Mounted UAV Millimeter-Wave Communications Across Diverse Scenarios: Path-Loss Model, Beam Management, and Posture Analysis

Oriented to low-altitude economy, integrated air-ground-space communication system and ultra-dense mobile communication network access, reconfigurable intelligent surfaces-mounted unmanned aerial vehicle (RIS-UAV) offer a dynamic solution for propagation challenges in millimeter-wave (mmWave) communications. This work aims to present a comprehensive analytical framework for RIS-UAV assisted mmWave communications in multiple scenarios, encompassing single-base station single-user terminal (SBSU), single-base station multi-user terminal (SBMU), multi-base station single-user terminal (MBSU), and multi-base station multi-user terminal (MBMU) scenarios. We first establish path-loss models and flexible beam management considering UAV translational and rotational posture movements separately within the SBSU scenario. For multi-user scenarios, we propose a space division multiple access (SDMA) over RIS scheme leveraging RIS element partitioning. For multi-base station scenarios, a mobile RIS-UAV phase coordination (MRUPC) strategy is proposed, utilizing the controlled mobility of the UAV to simplify phase compensation requirements for signals from multiple base stations. Extensive numerical simulations validate the accuracy of the derived path-loss model and the feasibility of the proposed beam management scheme for each scenario. The results demonstrate that SDMA over RIS effectively achieves multi-user mmWave beamforming. In addition, the proposed MRUPC strategy exhibits substantial performance gains (approx. 6-8 dB) over the static scheme in the MBSU scenario, validating the feasibility and superiority of leveraging UAV mobility for multi-base station coordination. This study comprehensively provides a systematic theoretical foundation and physical-layer solutions for the design and flexible deployment of joint RIS-UAV mmWave systems in complex wireless access scenarios.