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 MAs 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六维可移动天线系统，旨在提升通信性能。与传统固定位置天线（FPA）及现有流体天线/二维可移动天线（FA/2DMA）系统仅能调整天线位置不同，所提六维可移动天线系统由分布式天线面组成，这些天线面可在给定空间内独立调节三维位置及三维旋转角度。具体而言，本文将六维可移动天线应用于无线网络基站（BS），为基站提供完整自由度以适应网络中动态变化的用户空间分布。然而，如何基于用户空间分布，在六维天线运动实际约束下最优控制基站所有六维可移动天线面的六维位置与旋转角度以最大化网络容量，成为具有挑战性的新问题。为解决该问题，我们首先建立了配备六维可移动天线的基站模型及其与六维可移动天线面六维位置/旋转角度相关的用户信道模型。其次，提出一种基于蒙特卡洛模拟技术的交替优化算法，通过迭代方式依次优化每个六维可移动天线面的三维位置与三维旋转角度（同时固定其他天线面的对应参数），从而搜索全局最优解。数值结果表明，相较于采用固定位置天线或仅具有有限/部分可移动能力可移动天线的基准基站架构，所提六维可移动天线基站在用户分布空间非均匀性较强时可显著提升网络容量。