Six-dimensional movable antenna (6DMA) is an innovative technology to improve wireless network capacity by adjusting 3D positions and 3D rotations of antenna surfaces based on channel spatial distribution. However, the existing works on 6DMA have assumed a central processing unit (CPU) to jointly process the signals of all 6DMA surfaces to execute various tasks. This inevitably incurs prohibitively high processing cost for channel estimation. Therefore, we propose a distributed 6DMA processing architecture to reduce processing complexity of CPU by equipping each 6DMA surface with a local processing unit (LPU). In particular, we unveil for the first time a new \textbf{\textit{directional sparsity}} property of 6DMA channels, where each user has significant channel gains only for a (small) subset of 6DMA position-rotation pairs, which can receive direct/reflected signals from users. In addition, we propose a practical three-stage protocol for the 6DMA-equipped base station (BS) to conduct statistical CSI acquisition for all 6DMA candidate positions/rotations, 6DMA position/rotation optimization, and instantaneous channel estimation for user data transmission with optimized 6DMA positions/rotations. Specifically, the directional sparsity is leveraged to develop distributed algorithms for joint sparsity detection and channel power estimation, as well as for directional sparsity-aided instantaneous channel estimation. Using the estimated channel power, we develop a channel power-based optimization algorithm to maximize the ergodic sum rate of the users by optimizing the antenna positions/rotations. Simulation results show that our channel estimation algorithms are more accurate than benchmarks with lower pilot overhead, and our optimization outperforms fluid/movable antennas optimized only in two dimensions (2D), even when the latter have perfect instantaneous CSI.

翻译：六维可移动天线（6DMA）是一项创新技术，通过根据信道空间分布调整天线表面的三维位置与三维旋转来提升无线网络容量。然而，现有关于6DMA的研究均假设由中央处理单元（CPU）联合处理所有6DMA表面的信号以执行各项任务，这不可避免地导致信道估计的处理成本过高。为此，我们提出一种分布式6DMA处理架构，通过为每个6DMA表面配备本地处理单元（LPU）来降低CPU的处理复杂度。特别地，我们首次揭示了6DMA信道的一种新特性——**方向稀疏性**，即每个用户仅对一小部分6DMA位置-旋转组合具有显著信道增益，这些组合能够接收来自用户的直射/反射信号。此外，我们提出一种实用的三阶段协议，使配备6DMA的基站（BS）能够执行以下操作：对所有6DMA候选位置/旋转进行统计CSI获取、优化6DMA位置/旋转、以及在优化后的6DMA位置/旋转下为用户数据传输进行瞬时信道估计。具体而言，我们利用方向稀疏性开发了分布式算法，用于联合稀疏性检测与信道功率估计，以及基于方向稀疏性的瞬时信道估计。利用估计得到的信道功率，我们提出一种基于信道功率的优化算法，通过优化天线位置/旋转来最大化用户的遍历和速率。仿真结果表明，与基准方法相比，我们的信道估计算法在导频开销更低的条件下具有更高精度，且我们的优化方案性能优于仅在二维（2D）优化的流体/可移动天线方案，即使后者拥有完美的瞬时CSI。