In this paper, we propose a new six-dimensional (6D) movable antenna (6DMA) system for future wireless networks to improve the communication performance. Unlike the traditional fixed-position antenna (FPA) and existing fluid antenna/two-dimensional (2D) movable antenna (FA/2DMA) systems that adjust the positions of antennas only, the proposed 6DMA system consists of distributed antenna surfaces with independently adjustable three-dimensional (3D) positions as well as 3D rotations within a given space. In particular, this paper applies the 6DMA to the base station (BS) in wireless networks to provide full degrees of freedom (DoFs) for the BS to adapt to the dynamic user spatial distribution in the network. However, a challenging new problem arises on how to optimally control the 6D positions and rotations of all 6DMA surfaces at the BS to maximize the network capacity based on the user spatial distribution, subject to the practical constraints on 6D antennas' movement. To tackle this problem, we first model the 6DMA-enabled BS and the user channels with the BS in terms of 6D positions and rotations of all 6DMA surfaces. Next, we propose an efficient alternating optimization algorithm to search for the best 6D positions and rotations of all 6DMA surfaces by leveraging the Monte Carlo simulation technique. Specifically, we sequentially optimize the 3D position/3D rotation of each 6DMA surface with those of the other surfaces fixed in an iterative manner. Numerical results show that our proposed 6DMA-BS can significantly improve the network capacity as compared to the benchmark BS architectures with FPAs or 6DMAs with limited/partial movability, especially when the user distribution is more spatially non-uniform.

翻译：本文提出了一种面向未来无线网络的新型六维可移动天线系统，旨在提升通信性能。与仅能调整天线位置的传统固定位置天线以及现有流体天线/二维可移动天线系统不同，所提出的6DMA系统由分布式天线表面构成，这些表面可在给定空间内独立调节三维位置和三维旋转。特别地，本文将6DMA应用于无线网络中的基站，以提供完整的自由度，使基站能够适应网络中动态变化的用户空间分布。然而，由此产生了一个具有挑战性的新问题：如何在6D天线运动实际约束条件下，基于用户空间分布最优地控制基站所有6DMA表面的6D位置和旋转角度，以最大化网络容量。为解决该问题，我们首先建立了支持6DMA的基站模型，以及基站与用户之间关于所有6DMA表面6D位置和旋转角度的信道模型。其次，提出了一种高效的交替优化算法，利用蒙特卡洛仿真技术搜索所有6DMA表面的最优6D位置和旋转角度。具体而言，我们以迭代方式依次优化每个6DMA表面的三维位置/三维旋转，同时固定其他表面的对应参数。数值结果表明，与采用固定位置天线或有限/部分可移动6DMA的基准基站架构相比，所提出的6DMA-BS能显著提升网络容量，尤其在用户分布呈现更强空间非均匀性时效果更为突出。