Six-dimensional movable antenna (6DMA) is a promising solution for enhancing wireless network capacity through the adjustment of both three-dimensional (3D) positions and 3D rotations of distributed antenna surfaces. Previous works mainly consider 6DMA surfaces composed of active antenna elements, thus termed as active 6DMA. In this letter, we propose a new passive 6DMA system consisting of distributed passive intelligent reflecting surfaces (IRSs) that can be adjusted in terms of 3D position and 3D rotation. Specifically, we study a passive 6DMA-aided multiuser uplink system and aim to maximize the users' achievable sum rate by jointly optimizing the 3D positions, 3D rotations, and reflection coefficients of all passive 6DMA surfaces, as well as the receive beamforming matrix at the base station (BS). To solve this challenging non-convex optimization problem, we propose an alternating optimization (AO) algorithm that decomposes it into three subproblems and solves them alternately in an iterative manner. Numerical results are presented to investigate the performance of the proposed passive 6DMA system under different configurations and demonstrate its superior performance over the traditional fixed-IRS counterpart for both directive and isotropic radiation patterns of passive reflecting elements.

翻译：六维可移动天线（6DMA）是一种通过调整分布式天线面的三维位置和三维旋转来提升无线网络容量的有前景的解决方案。先前的研究主要考虑由有源天线单元构成的6DMA面，因此称为有源6DMA。在本通信中，我们提出一种新的被动6DMA系统，该系统由分布式被动智能反射面（IRS）构成，其三维位置和三维旋转均可调整。具体而言，我们研究一个被动6DMA辅助的多用户上行链路系统，旨在通过联合优化所有被动6DMA面的三维位置、三维旋转和反射系数，以及基站（BS）处的接收波束成形矩阵，来最大化用户的可实现和速率。为解决这一具有挑战性的非凸优化问题，我们提出一种交替优化（AO）算法，将原问题分解为三个子问题并以迭代方式交替求解。数值结果展示了所提出的被动6DMA系统在不同配置下的性能，并证明了其在被动反射单元具有定向和各向同性辐射模式时，均优于传统的固定IRS方案。