基于可移动单元的智能反射面辅助近场定位技术

Movable Reconfigurable Intelligent Surface-Aided Near-Field Localization

RIS在提高感知系统可靠性方面具有广泛的应用前景。同时,可移动天线技术可以利用天线的局部运动,动态地改变发射机和/或接收机处的天线位置,以优化信道条件,提高通信性能。因此,将可移动天线技术引入RIS,通过充分利用无线信道在有限区域的空间变化,进一步实现智能可控的无线信道传播环境。基于此,研究了一种基于可移动单元的智能反射面辅助近场定位技术。首先,提出了基于近场模型的最大似然定位算法,并推演出衡量定位性能的CRLB。然后,提出了一种基于投影梯度下降的交替优化算法,实现智能反射单元动态位置和波束赋形的联合优化,以获得RIS用于定位的优化结构和相位配置。仿真结果表明,与传统固定单元的RIS相比,通过灵活调整RIS反射单元的拓扑结构,获得更好的信道条件,能够显著降低用户位置估计的CRLB,提高系统的定位性能。

Reconfigurable intelligent surface (RIS) has broad prospects in enhancing the reliability of perception systems. Meanwhile,movable antenna can dynamically change the position of antennas at the transmitter and/or receiver by leveraging the localmovement of antennas for optimizing channel conditions and improving communication performance. Therefore, combiningmovable antenna with RIS can fully exploits the spatial variations of the wireless channel in a limited area to further realize anintelligent and controllable wireless channel propagation environment. Therefore, a near-field localization technique based on RISwith movable elements is investigated. Firstly, a maximum likelihood positioning algorithm is proposed with a near-field model,and the Cramér-Rao lower bound (CRLB) is derived to characterize the localization performance. Then, an alternating optimizationalgorithm based on projected gradient descent is proposed to achieve joint optimization of the dynamic positions and beamformingof RIS, and thus an optimized structure and phase configuration for RIS are obtained for localization. Simulation results show that,compared to traditional fixed RIS, flexible topology adjustment of RIS reflecting units can obtain better channel conditions, whichsignificantly reduces the CRLB of the user position estimation and improves system localization performance.