Different with conventional reconfigurable intelligent surface (RIS), simultaneous transmitting and reflecting RIS (STAR-RIS) can reflect and transmit the signals to the receiver. In this paper, to serve more ground users and increase the deployment flexibility, we investigate an unmanned aerial vehicle equipped with a STAR-RIS (STAR-RIS-UAV) aided wireless communications for multi-user networks. Energy splitting (ES) and mode switching (MS) protocols are considered to control the reflection and transmission coefficients of STAR-RIS elements. To maximize the sum rate of the STAR-RIS-UAV aided coordinated multipoint cellular system for multi-user networks, the corresponding beamforming vectors as well as transmitted and reflected coefficients matrices are optimized. Specifically, instead of adopting the alternating optimization, we design an iteration method to optimize all variables for both ES and MS protocols at the same time. Simulation results reveal that STAR-RIS-UAV aided wireless communication system has a much higher sum rate than the system with conventional RIS or without RIS. Furthermore, the proposed structure is more flexible than a fixed STAR-RIS and could greatly promote the sum rate.

翻译：与传统的可重构智能表面（RIS）不同，同时发射与反射的RIS（STAR-RIS）能够将信号同时反射和透射至接收端。为服务更多地面用户并提升部署灵活性，本文研究了搭载STAR-RIS的无人机（STAR-RIS-UAV）辅助的多用户网络无线通信系统。考虑采用能量分割（ES）和模式切换（MS）两种协议控制STAR-RIS单元的反射与透射系数。为最大化STAR-RIS-UAV辅助的多用户网络协调多点蜂窝系统的总速率，优化了相应的波束成形向量以及发射与反射系数矩阵。具体而言，本文设计了一种迭代方法，替代交替优化方案，同时优化ES和MS两种协议下的所有变量。仿真结果表明，STAR-RIS-UAV辅助的无线通信系统的总速率显著高于采用传统RIS或无RIS的系统。此外，所提出的结构相比固定式STAR-RIS更具灵活性，能够大幅提升总速率。