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：本文提出一种面向未来无线网络的六维可动天线（6DMA）系统，旨在提升通信性能。与仅能调节天线位置的固定位置天线（FPA）及现有流形天线/二维可动天线（FA/2DMA）系统不同，所提6DMA系统由分布式天线面构成，各天线面可在给定空间内独立调整三维位置与三维旋转。特别地，本文将6DMA应用于无线网络基站（BS），为基站提供完整自由度（DoFs）以适配网络中动态的用户空间分布。然而，如何基于用户空间分布优化控制基站所有6DMA面的六维位置与旋转以最大化网络容量，同时满足6D天线移动的实际约束，成为一个具有挑战性的新问题。为解决该问题，本文首先建立了6DMA赋形基站及用户信道的模型，该模型将基站特性表示为所有6DMA面的六维位置与旋转的函数。继而提出一种高效的交替优化算法，通过蒙特卡洛仿真技术搜索所有6DMA面的最优六维位置与旋转：具体地，以迭代方式依次优化每个6DMA面的三维位置/三维旋转，同时固定其余各面的对应参数。数值结果表明，与采用FPA或有限/部分可动6DMA的基准基站架构相比，所提6DMA-BS能显著提升网络容量，尤其在用户空间分布非均匀性增强时优势更为明显。