The capacity of commercial massive multiple-input multiple-output (mMIMO) systems is constrained by the limited array aperture at the base station, and cannot meet the ever-increasing traffic demands of wireless networks. Given the array aperture, holographic MIMO with infinitesimal antenna spacing can maximize the capacity, but is physically unrealizable. As a promising alternative, reconfigurable mMIMO is proposed to harness the unexploited power of the electromagnetic (EM) domain for enhanced information transfer. Specifically, the reconfigurable pixel antenna technology provides each antenna with an adjustable EM radiation (EMR) pattern, introducing extra degrees of freedom for information transfer in the EM domain. In this article, we present the concept and benefits of availing the EMR domain for mMIMO transmission. Moreover, we propose a viable architecture for reconfigurable mMIMO systems, and the associated system model and downlink precoding are also discussed. In particular, a three-level precoding scheme is proposed, and simulation results verify its considerable spectral and energy efficiency advantages compared to traditional mMIMO systems. Finally, we further discuss the challenges, insights, and prospects of deploying reconfigurable mMIMO, along with the associated hardware, algorithms, and fundamental theory.

翻译：商用大规模多输入多输出（mMIMO）系统的容量受限于基站有限的阵列孔径，无法满足无线网络日益增长的流量需求。在给定阵列孔径的条件下，具有无限小天线间距的全息MIMO可最大化容量，但物理上难以实现。作为一种有前景的替代方案，可重构mMIMO被提出以利用电磁（EM）域中尚未开发的潜力来增强信息传输。具体而言，可重构像素天线技术为每根天线提供可调的电磁辐射（EMR）模式，在电磁域中引入额外的信息传输自由度。本文阐述了利用EMR域进行mMIMO传输的概念与优势，并提出了可重构mMIMO系统的可行架构，同时讨论了相关系统模型与下行预编码方案。特别地，本文提出了一种三级预编码方案，仿真结果验证了其相较于传统mMIMO系统在频谱效率和能量效率方面的显著优势。最后，本文进一步探讨了部署可重构mMIMO所面临的挑战、见解与前景，以及相关的硬件、算法和基础理论。