Reconfigurable massive multiple-input multiple-output (RmMIMO), as an electronically-controlled fluid antenna system, offers increased flexibility for future communication systems by exploiting previously untapped degrees of freedom in the electromagnetic (EM) domain. The representation of the traditional spatial domain channel state information (sCSI) limits the insights into the potential of EM domain channel properties, constraining the base station's (BS) utmost capability for precoding design. This paper leverages the EM domain channel state information (eCSI) for antenna radiation pattern design at the BS. We develop an orthogonal decomposition method based on spherical harmonic functions to decompose the radiation pattern into a linear combination of orthogonal bases. By formulating the radiation pattern design as an optimization problem for the projection coefficients over these bases, we develop a manifold optimization-based method for iterative radiation pattern and digital precoder design. To address the eCSI estimation problem, we capitalize on the inherent structure of the channel. Specifically, we propose a subspace-based scheme to reduce the pilot overhead for wideband sCSI estimation. Given the estimated full-band sCSI, we further employ parameterized methods for angle of arrival estimation. Subsequently, the complete eCSI can be reconstructed after estimating the equivalent channel gain via the least squares method. Simulation results demonstrate that, in comparison to traditional mMIMO systems with fixed antenna radiation patterns, the proposed RmMIMO architecture offers significant throughput gains for multi-user transmission at a low channel estimation overhead.

翻译：可重构大规模多输入多输出（RmMIMO）作为一种电子控制的流体天线系统，通过利用电磁域中先前未被开发的自由度，为未来通信系统提供了更高的灵活性。传统空间域信道状态信息（sCSI）的表征方式限制了对电磁域信道特性潜力的深入理解，从而制约了基站在预编码设计方面的最大能力。本文利用电磁域信道状态信息（eCSI）进行基站天线辐射方向图设计。我们提出了一种基于球谐函数的正交分解方法，将辐射方向图分解为正交基的线性组合。通过将辐射方向图设计表述为这些基上投影系数的优化问题，我们开发了一种基于流形优化的迭代辐射方向图与数字预编码器设计方法。针对eCSI估计问题，我们利用信道的内在结构特性，提出了一种基于子空间的方案以降低宽带sCSI估计的导频开销。在获得估计的全频带sCSI后，我们进一步采用参数化方法进行到达角估计。随后，通过最小二乘法估计等效信道增益即可重构完整的eCSI。仿真结果表明，与采用固定天线辐射方向图的传统大规模MIMO系统相比，所提出的RmMIMO架构能够以较低的信道估计开销为多用户传输带来显著的吞吐量增益。